More Desert Gardening

I have come to know the Anza-Borrego Desert fairly well over the last 15 years. There is a lot more complexity and variety than I originally expected. The following photos illustrate some of the landforms and ecotypes that make up this desert.

Rocky hills and mountains

Desert Washes - this one is Fish Creek

Alluvial fans and bajadas

Badlands

Steep walled slot canyons

Canyons with year-round water

Desert Transition Chaparral at higher elevations

Borrego Valley

As I mentioned in my last post, my philosophy of gardening is to use plants that would normally be found where the garden is located. I need to add a phrase to that: "...or reasonably nearby." In my Encinitas garden I use plants from other parts of California and Baja, as long as I can create suitable conditions for them without extraordinary measures. 

The same principle applies in my Borrego Springs garden. My garden is located in the Borrego Valley. I could restrict myself to plants that are native to the valley where the dominant plant community is Creosote Bush Scrub, but that would eliminate a number of plants that I want to grow, including some Baja species. So my task is to try to replicate the conditions in which these other plants would normally occur. Desert wash species such as Smoketree (Psorothamnus spinosus) can do just fine in the valley if I put it in deep, loose sand and give it an occasional flood. Plants found higher up in the rocky hills can do okay if I surround them with lots of rocks. This method doesn't work perfectly because my knowledge of what plants want isn't perfect. But it has been reasonably successful.

In this post I want to continue the discussion of trees, this time focusing on the Palo Verde group (genus Parkinsonia, formerly classified as Cercidium). The most common Parkinsonia in this area is Blue Palo Verde (P. florida). It is a handsome, fast growing, relatively trouble-free tree. One of the special adaptations of all Parkinsonias is the smooth green bark on the trunk, branches and twigs, which is the origin of the name Palo Verde. The bark contains chlorophyll so the tree can conduct at least some photosynthesis even when all the leaves are gone. As the tree ages its lower trunk loses the green color and becomes a more typical rough, brown bark. The blue-green leaves are small, like those of Ironwood and many other desert plants, which helps conserve water but cuts down on photosynthetic productivity. Green bark helps make up for this shortcoming. Here's one of the Blue Palo Verdes in my garden.

This tree is approaching 10 years old. Blue Palo Verdes are not terribly long-lived, but their longevity is improved by not giving them too much water. Although they will accept any amount of water you want to give them, the result in often excessively fast growth, brittle limbs, and short life span. I recommend weaning them off supplemental water after the first year. Blue Palo Verdes accept pruning well, but they do have some spines so use gloves when handling. One of the best features of Blue Palo Verde is the flowers which come out in late spring or summer.

Here are the seed pods, which are edible but reportedly not as tasty as Mesquite.

There is a hybrid variety called 'Desert Museum' which many people like because it has no spines. I'm not big on hybrids but this one does seem to be a good choice.

The next species of Parkinsonia is Little Leaf Palo Verde or Foothill Palo Verde (P. microphylla) which grows in Imperial, Riverside and San Bernardino Counties and Baja. It differs from Blue Palo Verde in having even smaller leaves and slightly smaller stature, but otherwise they are quite similar. 

The flowers look very similar to Blue Palo Verde, but the seed pods look a little different.

Both of the above species have produced seedlings around my yard after a winter of good rainfall.

The last Parkinsonia that I have in my garden is called Palo Brea (Parkinsonia praecox). It is a Baja species that does not occur in the wild north of the border. Jon Rebman says it occurs from the Sierra San Francisco south to the Cape Region and a few spots in South America. I like it because it has a slightly different appearance from the other two and works well in Borrego Springs. In my experience it has not been a prolific seed producer, so it would appear that its chances of become invasive are low.

One member of this genus that I do not recommend is Mexican Palo Verde (P. aculeata). It is more weedy than other Parkinsonias and could become invasive in California deserts, although it is said to be better behaved near the coast. Pacific Horticulture Magazine says, "Since both its growth and seed production are markedly stronger where temperatures are high, in some parts of the world where it has been introduced, it has become a weed species that can overwhelm weaker indigenous plants." It has already become a noxious weed in Australia. Unfortunately, it is popular with some landscapers and homeowners because it is even faster growing than Blue Palo Verde. Its fast growth makes it brittle, poorly shaped and short-lived, but apparently some people don't know or don't care about that. It could also hybridize with native Palo Verdes and introduce undesirable genetics into local populations. The 'Desert Museum' hybrid Palo Verde that I mentioned earlier is reportedly a three-way cross between P. aculeata, P. Florida and P. microphylla. This kind of controlled and intentional hybridization may be a good thing, but random hybridization in wild populations is definitely not. If you want the look and performance of a Palo Verde, choose one of the others.

Parkinsonia aculeata (Mexican Palo Verde)     Photo by Carolyn Martus

 That's all for the Palo Verdes in my garden.

A Desert Garden

Many people think that southern California is all desert, but that isn't really true. The confusion comes from the seasonally arid nature of the Mediterranean climate which, to people who come from other areas, feels a lot like desert weather. However, we do have true desert in San Diego County, about 90 miles east of the coast. The differences between the coast and the desert are dramatic, in terms of climate and ecology.

Borrego Springs

 In April 2001 my wife and I bought a very rundown old house in Borrego Springs. We have fixed it up and use it as a weekend getaway. One of my primary reasons for buying this house was to have a native desert garden. I have been working on this garden for amost 15 years and I'm now ready to start blogging about it. Thus, I am departing from the "Encinitas" nature of this blog and expanding into the more general discussion of gardening with California native plants throughout the state. First, here's a couple of early shots of our house in Borrego Springs...

 It sits on an acre lot with about 10 acres of vacant lots around it. Plenty of room to do some gardening. There wasn't a lot of landscaping when we bought it and the house was in very rough condition. What it did have was lots of rocks (always good), and some really large, mature barrel cactus (Ferocactus cylindraceus). There was also a big, old Ocotillo (Fouquieria splendens) in the front yard and three palms (I think two are native Washingtonia filifera and one is W. robusta).

 The biggest problem area was the west side of the house which had very compacted, bare soil. I think the previous residents must have parked heavy vehicles on it. To be able to garden there, I had to bring in some loads of loose sand to create artificial dunes. Then I was able to plant. My gardening philosophy there as well as in Encinitas is to use plants that would normally be found growing wild in that area. I think this just makes sense because those plants are going to be the easiest to grow with the least amount of human intervention. They are also going to fit best into the local ecology, and they will "look right" in that area.

I started with a number of trees. The first is a Desert Ironwood (Olneya tesota). This tree is found in a number of locations in the Anza-Borrego area as well as parts of Arizona and Baja. It is a very attractive tree in the Fabaceae (Legume) family, slow growing but worth the wait. The one I planted was a 15 gal. about 2 ft. tall. It is doing very nicely, still not huge but quite healthy and happy. I planted it right on top of one of the new dunes so that it would have plenty of room for root growth and very fast drainage.

Ironwood is an interesting plant because its wood is so dense that it will not float. In Baja the wood is used to carve curios for tourists to buy. It also makes very long-lasting firewood, but that seems like such a waste. It has very small, grey-green leaves for water conservation, and it will drop its leaves in very dry periods (usually summer). It will leaf out in response to winter rain. It has spines so caution should be used in working around it. It is usually found on alluvial fans and bajadas that are dry in summer but have subsurface water in winter. It blooms in summer with very pretty flowers that few people see due to the summer heat. Below is a photo (sorry, it's not in very good focus) of my Ironwood in bloom. Now that this tree is well established, it requires almost no supplemental water and minimal care.

Here's a shot of a mature tree in the wild in Borrego Palm Canyon.

 

Another tree I planted was a Desert Willow (Chilopsis linearis). This tree is almost the complete opposite of Ironwood. It is in the Bignoniaceae (Begonia) family. It's origin was probably tropical, and it looks like it. It has long, bright-green leaves. The leaves resemble those of willow species (genus Salix) which led to the common name. It drops its leaves and goes dormant in winter. It is typically found in desert creeks or wet areas where there is year-round water. It blooms from late spring into summer with large, extravagant flowers of pink, purple and white. It has some resemblance to Oleander and can be used as an effective substitute. It's biggest drawback is the fact that it is deciduous in winter; that's when most people are in the desert and they want their plants to look good.

The other important thing to note about Desert Willow is that it must be kept watered, unlike most other desert plants. To accomplish this, I planted mine in a shallow basin in the sand, not on one of the dunes. I put a bunch of rocks in this depression to mimic a stream. When I think it needs water, I put the hose into the rocks and flood the basin. The rocks help keep the soil moist for a long time, so I don't need to water it all that often, maybe once a month. This is a great tree for using greywater. If you could run an outlet hose from your washing machine out to a Desert Willow, it would be the happiest tree in the world.

One more tree that I planted early was Smoketree (Psorothamnus spinosus). This is a truly iconic tree of the desert with a totally unique appearance. Its grey-green, almost leafless stems really do look a bit like smoke from a campfire when seen in the distance. Smoketrees grow in desert washes where the sand is very deep and there is a dependable supply of subsurface water. below are some Smoketrees in the Split Mountain wash.

I took a big risk with the Smoketree that I bought because it is a notoriously tricky tree to get established. It has a deep taproot that helps it find water in desert washes, and this taproot can get damaged easily when in a container or in moving it from container to ground. The ideal way to grow Smoketree would be from seed, but that's not easy either. The seed must be scarified and/or soaked before sowing. This usually occurs in a big storm that tumbles the seeds in the sand of a wash. Surprisingly, a lot of smoketrees pop up on road shoulders in Borrego Springs when there is a mature tree nearby. The seeds get scattered out on the road and get run over by cars which scarifies them. Then winter rain triggers germination. Below is a photo of one such tree.

My big risk was that I bought a 24" box tree, and it was expensive. Fortunately, it has done well. As with the Desert Willow, I did not plant it on a dune. I just felt it would do better on flat ground. Below is a photo of it in my garden.

 

Smoketrees have terminal spines. That is, the stem ends in a very hard, sharp point. 

 

On the plus side, the flowers are beautiful. Like Ironwood, it blooms in late spring or summer and many people never see it. Also like Ironwood, it is in the Fabaceae (Legume) family. In fact, very many of the native trees and shrubs of the desert are in this family, including Palo Verde, Mesquite and Indigo Bush. They all have typical "pea" flowers and seed pods. I'll highlight more of these in future posts.

That's all for now.

Bulbs and Corms

This post and the previous one are based on an article from the Fall 2007 issue of Fremontia: Journal of the California Native Plant Society. That issue was a special edition on chaparral. The article I'm focusing on this time is "Chaparral Geophytes: Fire and Flowers" by Claudia Tyler and Mark I. Borchert.

Geophytes are plants that grow from a bulb or corm. I will refer to all of them as "bulbs" for simplicity. California has lots of great geophytes that are wonderful to see in the wild and also beautiful garden plants. Geophytes can be found in several habitats including grasslands, coastal sage scrub and chaparral. The Fremontia article addressed what happens to geophytes in chaparral before and after a fire.

Inflorescence of  Chlorogalum pomeridianum in my garden. Its common name, Soap Plant, comes from the fact that Native Americans used the bulb to make a version of soap

The authors of the article did their study in the mountains of Ventura and Santa Barbara Counties. They studied two species, Toxicoscordion (formerly Zigadenus) fremontii, commonly known as Fremont's Star Lily, and Chlorogalum pomeridium (Soap Plant). I believe their findings may also apply, at least in part, to other geophyte genera including Bloomeria, Brodiaea, Calochortus, Dichelostemma, Hesperocallis, Triteleia, and others.

Their first finding was that flowering and seed production are almost completely limited to the first year after a fire. And they don't just make a flower or two. They produce an extravagant display. It appears that the trigger for flowering is the increased light that the geophytes receive once the larger shrubs are removed. It isn't necessarily fire that does the job. Pruning could accomplish the same thing, but fire is the more common cause of shrub removal in the wild. In any case, giving a geophyte a big blast of sunlight results in both dramatic flowering and subsequent seed production.

What happens the next year? The plants shrank after flowering and typically do not flower again for several years. It seems that the energy required to produce a showy display of flowers comes from drawing stored food from the bulb. In so doing, the plant is considerably depleted. It has to rebuild that reserve of food in the bulb by putting out foliage for photosynthesis but no flowers. When geophytes do flower, the ones with the biggest bulbs produce the most flowers and seeds, and it takes time to build up a large bulb.

So geophytes actually need two things to flower: (1) lots of sunlight, and (2) enough energy stored in the bulb. 

Brodiaea filifolia (Thread-leaf Brodiaea) in my garden

The seeds produced after flowering need to germinate during the winter following the bloom. Any seeds that don't germinate will likely be eaten by insects or small mammals. Unlike many other chaparral plants, geophyte seeds don't have much longevity and so don't build up a seed bank in the soil. Seedlings have to get established and start building up a bulb in order to survive. Furthermore, seeds aren't the only things that get eaten. Gophers and some other burrowing animals will eat the bulbs. I think this explains in part why geophytes are not more numerous.

In still later years the chaparral shrub cover once again deprives the geophytes of light. Do they stop growing? No, just the opposite. Geophytes in mature chaparral use whatever light they can get to grow substantially. Without the energy drain of flowering, they can save up a lot of carbohydrates in the bulb, trying to get that bulb as big as possible before it has to bloom again. In really mature chaparral areas it could be 50 years or more between fires, and thus also between blooms.

I have a lot of Dichelostemma capitatum in my garden. I got the original bulbs from a former friend who lived a couple of miles away in Encinitas. His lot had a small section of native slope that had Dichelostemma and non-native grasses. He did not appreciate the beauty of the flowers and he was planning to regrade that slope in order to build something on it. He let me dig up the bulbs first. I got about 100 of them, and I picked out the biggest ones. I didn't know about the relationship between bulb size and flowering, but I couldn't take all the bulbs so I just went for the biggest ones. I set up a dedicated area for them with no competing plants and I planted them densely, the way they were growing previously. I left the soil bare.

Dichelostemma capitatum in my garden several years ago

They did really well in my garden right from the start, with lots of flowering. My guess is that they responded as they would have after a fire. After that, their flower production seemed to decline and at that time I didn't know why. Now, after reading this article I understand that they needed to rebuild their energy reserves. Their relative lack of flowering was counterbalanced by their reproduction. Lots of seedlings came up and many survived. Later, I observed that the larger bulbs were producing bulblets, little baby bulbs. My original 100 has expanded to 200 or more. I dug out some bulbs to get them going in other areas. 

Bulb of Dichelostemma with bulblets

Many years later, an oak tree that I planted nearby got much bigger and now shades the Dichelostemma area all afternoon. They still get some sun, just not all day. I noticed that flower production went down further, but leaf growth ramped way up. The bulbs are now putting out huge, lush, floppy leaves that don't even look like Dichelostemma leaves. When this first started happening I thought the leaf growth was excessive and might be interfering with flowering, so I trimmed off some of the leaf growth. It was like mowing a lush lawn; the leaves grew right back in a couple of weeks. Now I understand (I think) what is going on. As the article suggested, when geophytes are shaded by chaparral shrubs they go into the mode of energy production and storage. In the first couple of years after I planted them in my yard they were experiencing something like the first couple of years after a fire, with abundant sunshine and no competition. Now they are hunkering down, photosynthesizing as much as they can, and storing up food for the day when a fire will trigger them to flower profusely once more.

I have seen a similar dynamic with Brodiaea filifolia. It is not a chaparral species, occurring in either vernal pools or grasslands. But I think it is similar to the other geophytes in that it needs a recovery period after flowering. The production of flowers and seeds takes a lot out of a plant. It needs a few years to get back to where it was before it flowered. So you don't see all the Brodiaea bulbs in a population flowering at the same time. In a given year, a few are flowering while most are in some stage of recovery.

Calochortus species occur in a lot of different habitats including chaparral, and I think the foregoing applies to them as well. I had to buy Calochortus bulbs and they are a bit pricey so I have tended to plant just one or two at a time. This also matches the way I have seen them growing in the wild, not in dense patches but singly mixed with other plants. I have planted Calochortus bulbs that flowered extravagantly the first year. Then I never saw them again for years. I now believe they are still there in the soil, slowly growing, gradually recovering from the toll of their last flowering episode.

Calochortus venustus in flower, Spring 2010. Bloomed again in 2014.

 In an earlier post I described buying some Bloomeria crocea bulbs and planting them in the garden. I bought ten bulbs and planted them in an area where I already had three. They didn't all bloom last year, but several did. I planted a Salvia brandegeei nearby and it is now covering the Bloomeria space. It will be interesting to see if any bloom this coming spring.

 My new approach to geophytes in the garden is to alter my expectations about flowering. I will probably get abundant flowering the first year. After that I should expect several years of few or no flowers while the bulbs recover. If some of my other plants shade out the bulbs, that's not necessarily a problem as it mimics the natural dynamic in chaparral. Eventually, though, the bulbs would like to get full sun exposure again. I can either wait for natural changes in the garden to provide this or I can make it happen by strategic pruning. But I don't need to be in any hurry about this. The longer the interval between flowering episodes, the bigger the bulbs will get so that the next bloom will be even more dramatic.

Manzanita Reproduction

I recently came across Fall 2007 edition of Fremontia, the Journal of the California Native Plant Society. This edition was a special issue devoted to Chaparral. I love Fremontia and I especially love this special edition. There were two articles that particularly impressed me. One dealt with the Manzanitas and Ceanothus (primarily Arctostaphylos spp.) and the other dealt with geophytes, ie. plants that arise from bulbs or corms. In this post I'm going to summarize the article on Manzanitas and talk about how it applies to gardening with natives and to my garden in particular.

New Growth on Del Mar Manzanita (Arctostaphylos glandulosa ssp. crassifolia) in my front yard

The Manzanita article was titled Diversity and Evolution of Arctostaphylos and Ceanothus by V. Thomas Parker. The author explained that there are two main lineages of Arctostaphylos, and these are differentiated by how they respond to fire. The two types are burl-formers and obligate seeders. This in itself is a fascinating fact. It suggests that there was a parent taxon somewhere in the past 1.5 million years that was subjected to episodic fire, with some of its offspring responding one way and others responding another way. 

Burl-formers are also called stump-sprouters and crown-sprouters. The burl is an enlarged woody rootstock or junction between the trunk and the roots. Here's how the sprouters work: these species are capable of producing new growth from the burl after a fire as long as the burl is not irrevocably damaged. The top of the burl usually gets charred, but the rest of it is very tough and mostly underground, so it's usually okay unless the fire is unusually hot. New growth comes out from the undamaged part of the burl. All branches can be destroyed, but if the burl is not totally burned up new branches will sprout out almost immediately after the fire, often within days. Burl-formers do produce seeds, and some of them do germinate after a fire, but the majority of seedlings die within a year or two (unless the fire is exceedingly hot and a large number of burls are destroyed). In general, seedlings can't complete with re-sprouting burls that have huge, intact root systems.

I should mention here that Arctostaphylos isn't the only genus that uses stump-sprouting after fires. Heteromeles arbutifolia (Toyon) and Xylococcus bicolor (Mission Manzanita) also stump-sprout, as do many others. It's a fairly common chaparral adaptation to fire.

Arctostaphylos rudis (Sand Mesa Manzanita) in San Luis Obispo County.
Photo by Akos Kokai [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)]

Manzanitas that are obligate seeders do not form a burl and are typically killed outright by fire. However, obligate seeding species of Arctostaphylos outnumber the sprouters, and their response to fire is equally effective because they produce lots of seeds that are primed to germinate by the chemicals in smoke. Germination is not immediate, but when the first rains come after the fire, germination is rapid and widespread. There are no old plants to compete with the seedlings, and an entirely new generation is created. Thus, both lineages of Arctostaphylos are able to come back after a fire. There are limitations to each approach, but in a system that is not too screwed up by people both lineages do well. The key difference between the two lineages is what it means for their genetics. This is where it gets really amazing.

Los Padres National Forest, Aug. 2009
Photo by Airman 1st Class Andrew Lee

The burl-formers don't experience a lot of genetic change over time because the original plants are simply regenerating themselves. The fire has changed nothing in the genes of these plants. On the other hand, obligate seeders experience a lot of genetic change with each fire. It isn't that fire directly causes genetic change. Rather, fire kills all the adult plants in the burned area, wiping out that generation in that place. The thousands of seeds which have lain dormant in the soil for many years or decades will have slightly different genetics from their parents, the result of unique combinations of pollen and ovules. It makes for essentially 100% genetic turnover in the local population. The new genetic diversity created by this event creates some plants that are very well suited to their environment and others that are not so well suited. It should also be noted that Manzanitas of both lineages tend to hybridize readily, and over time all this cross-fertilization and hybridization by obligate seeders will produce enough genetic variation to form new taxa (species, subspecies and varieties). Hybridization doesn't mean as much for the burl-formers because production of new plants from seed is less important to their short-term survival. 

The behavior of obligate seeders is most dramatically seen in the Arctostaphylos-dominated chaparral communities of the central coast. I'm going to throw around some numbers from Parker's article. California is home to about 95 taxa of Arctostaphylos; 42 of these occur in the narrow coastal band between the San Francisco Bay and Monterey Bay; 32 of these are referred to as "narrow endemics" that are restricted to very small geographic areas. Plus, there are several more narrow endemics between Monterey and Santa Barbara. Many of these are are on the CNPS Inventory of Rare and Endangered Plants. Why is this a big deal? Virtually all of these narrow endemic Manzanitas are obligate seeders, and this is the key to their rarity. 

In Monterey County alone the following 14 rare taxa are found (each species name below is clickable and will take you to the appropriate page on Calflora):

• A. andersonii (Heartleaf Manzanita)
• A. cruzensis (La Cruz Manzanita)
• A. edmundsii (Little Sur Manzanita)
• A. gabilanensis (Gabilan Mountains Manzanita)
• A. glutinosa (Shreiber's Manzanita)
• A. hookeri ssp. hookeri (Hooker's Manzanita)
• A. hooveri (Hoover's Manzanita)
• A. luciana (Santa Lucia Manzanita)
• A. montereyensis (Toro Manzanita)
• A. obispoensis (Serpentine Manzanita)
• A. parjaroensis (Pajaro Manzanita)
• A. pechoensis (Pecho Manzanita)
• A. pilosula (La Panza Manzanita)
• A. pumila (Dune Manzanita)

What the above points out is the fairly incredible amount of genetic diversity generated by the obligate seeders of the central coast. In every little micro-climate and micro-niche there is a Manzanita that is specifically adapted to the conditions found there. It is also noteworthy that in this central coastal strip fire is currently not as common as it is in warmer and more arid parts of the state. Burl-formers would have no particular advantage in the absence of fire, but also the obligate seeders would have fewer opportunities to get rid of the old generation and start a new one. Parker states that these narrow endemics have evolved quite recently, in the last 10,000 to 20,000 years, suggesting that this amount of speciation occurred very rapidly as a result of just a few major fire events.

One implication of the foregoing is that the obligate seeder taxa are potentially not very stable in the long run. A big fire in Monterey County could wipe out one or more rare species, and the seedlings that would emerge after the fire would be different from the parents in ways we cannot predict. All of these rare species will have hybridized with each other and with more common species. Each seedling would have slightly different genetics, and it would take years to see which ones would survive and dominate. The chances of the original species reestablishing themselves after such an event is slim.

Manzanita in My Garden. I live in San Diego County, not the central coast, so the Arctostaphylos species here are naturally going to be different from those in Monterey or Santa Cruz. There are some rare species of Manzanita in my region, but only a handful compared with the 14 found in Monterey County. One of San Diego's rare taxa is A. glandulosa ssp. crassifolia (Del Mar Manzanita), and I am fortunate to have a nice specimen of it (shown in the photo below). The basic species A. glandulosa is quite widespread, occurring in the coastal strip from Oregon to Baja. However, ssp. crassifolia is limited to a very small ribbon of southern maritime chaparral between Torrey Pines and Carlsbad. You can see it on the Calflora map. Zoom in on San Diego County to see exactly where it is found. A. glandulosa has a number of other subspecies as well. Some are common and some are rare. An academic paper on the species states: "Particularly in the southern half of its range it exhibits complex patterns of morphological variation that have long presented taxonomic challenges." (Subspecific Variation in the Widespread Burl-Forming Arctostaphylos glandulosa, Jon E. Keeley, Michael C. Vasey and V. Thomas Parker. Madrono, Vol. 54, No. 1, pp. 42–62, 2007).

A. glandulosa ssp. crassifolia with flowers and fruit in my front yard

Is ssp. crassifolia a sprouter or a seeder? It does both. It has a burl and after fire it sprouts from the burl. But the seeds are also activated in response to fire. This dual approach is called Facultative Seeder. Perhaps this helps explain the rarity of ssp. crassifolia, as well as the taxonomic challenges of the many subspecies. Under ordinary conditions it would be expected that stump sprouting would dominate after fires, producing genetic stability. Seedlings would come up but these would typically not survive. But suppose there were some fires in the past which killed all the mature A. glandulosa plants in a given area, destroying all the burls. This can happen in an extremely hot fire. Then recruitment from seeds would have taken over. The new genetic diversity contained in these seeds would have created numerous new versions of A. glandulosa, some of which would have been especially well suited to a particular soil or micro-climate. The one that became ssp. crassifolia would have been a seedling that was best adapted to the sandstone soil and mild, maritime climate where it occurs, while other versions of the same species would be better adapted elsewhere. In response to subsequent low-intensity fires, individuals of ssp. crassifolia would stump sprout, maintaining stable genetics in the subspecies. I would expect ssp. crassifolia to remain stable until the next catastrophic fire in which most or all of the ssp. crassifolia burls are destroyed. Then we might get entirely new subspecies or varieties arising from all the seeds in the soil. In this scenario, unburned individuals of ssp. crassifolia, such as those in gardens, might be the only source for the original genes of the taxon. This is just speculation on my part and I may have it completely wrong, but I think it makes sense.

Mojave Yucca (in bloom), Dudleya, Summer Holly, Del Mar Manzanita, and Toyon in my front yard

Taxonomists must go crazy trying to sort out all these variations in Arctostaphylos. Or maybe they love it. In addition to all of these species, subspecies and varieties, we have other genera that exhibit similar traits, including Comarostaphylos, Ornithostaphylos, and Xylococcus, all in the same family. In a more recent Fremontia (May 2015), Lee Gordon and several co-authors examined the reproductive behavior of Mission Manzanita (X. bicolor). In view of its apparently low seedling survival rate, they asked whether Mission Manzanita is in decline. It, too, is concentrated in San Diego County. Over the eons it seems to have been more stable genetically than Arctostaphylos. I say that because there is only one species in the genus, and no subspecies or varieties. My guess is that it is a Facultative Seeder that can reproduce from seed but seldom needs to, much like Del Mar Manzanita. But unlike Del Mar Manzanita it never experienced a fire that wiped out a whole generation and triggered massive seedling production, with its attendant explosion of genetic diversity. Is this possible? I don't know. Once again I am just speculating. But it is indisputable that Mission Manzanita relies heavily on stump-sprouting, rarely reproducing from seed, and appears to remain extremely stable genetically. Or at least it looks that way to me.

The Bottom Line is that plants must use sexual reproduction (seeds) in order to achieve genetic variability. They can't get any variation from stump-sprouting. The same could be said of plants that reproduce vegetatively, such some of the cholla cacti which produce clones. But stump-sprouting isn't even reproduction, it's just continued growth of the same individual. Stump-sprouting gives individual plants the ability to live a long time and to withstand most (but not all) fires. Seed reproduction, on the other hand, gives the species as a whole the opportunity to develop new genetic strains which may have enhanced survival value in a given place and time. So the Arctostaphylos species in California give us an interesting picture of the adaptive trade-offs between these two different strategies for responding to fire.

In Part II I will talk about the geophytes and their unique response to fire.

Strange New Resident

The other day I found this thing on our lime tree. Why do we have a lime tree in my mostly native garden? My wife wanted it. So anyway, this thing looked like a very large bird poop, but I knew it wasn't that. After more looking I found a second one. Here's my best photo of it.

I believed I'd seen these before but couldn't remember exactly. After consulting with my entomologist friend, I learned that they are the larvae of a Giant Swallowtail butterfly (Heraclides cresphontes). Then I recalled briefly seeing an adult swallowtail of some type flitting about the lime tree about two weeks ago. It was an impressive butterfly but I couldn't identify it, so I grabbed the camera and shot a few pictures while it was flying about. They aren't great pictures because it wouldn't stop moving, but they do document what is was and the egg laying activity (see photo further down).

Back to the larvae, they are called Orange Dogs. I believe the orange reference is to the fruit because they feed on citrus plants and they clearly aren't orange in color. As far as the dog reference, look at the face on this one. The larva's resemblance to bird poop is probably pretty effective camouflage. They are also distasteful to birds and can emit a foul odor if threatened.

This species was previously quite rare in California. They have spread from the southeast through Texas and the southwest and are now becoming more established here. They reportedly don't do significant damage to plants. I'm relieved at that because it means the big citrus growers won't be targeting it for eradication. Still, commercial citrus groves are probably no good for this species because they are sprayed with so many pesticides. Organically grown citrus in home gardens is probably their best place for egg laying.  

The adult is said to be the largest butterfly in North America, with a wing span of up to 6 inches. I can believe it based on the size of the larvae and the one I saw laying eggs in October.The chrysalis will resemble a dried, curled up leaf which may make it difficult for me to find. As an adult it will only live about 2 weeks, but that should be long enough for it to find a mate and lay more eggs.

A funny thing about this photo is that there is already a larva on a leaf in the upper right corner of the photo. I never saw it when I was taking the photo because I was focused on the butterfly, and I never saw it when reviewing the photos. I only saw it after cropping the photo to include it here. It makes me think about how many interesting thing I probably miss every day.

It's Planting Time!

In many ways, fall is my favorite time of year. One of the key reasons is that I can buy new plants and add them to my garden. One reason I need new plants is that a few things died over the summer. I spent 6 weeks in Virginia communing with the White Oaks, Chestnuts and Virginia Creeper. Some of my plants that I thought would be fine without water for 6 weeks turned out to be not fine, even though SD got some rain while I was gone. One that surprisingly bit the dust was Yerba Santa (Eriodictyon crassifolium). When I left it was looking great. When I got back it looked like this.

Oh well. Everything else around it is fine. Sometimes these things just happen.

Some plants, on the other hand, are doing really well, in particular the Baja plants. My theory is that plants from areas that receive mostly summer rain did especially well this year. An example is Cape Wild-Plum (Cyrtocarpa edulis). It is a Baja endemic from the cape region where most rain falls in summer and there is rarely any winter rain. I bought it as a bare root from Arid Lands Nursery and put it in a medium size container. I wasn't sure at first that it was going to survive. But after this summer it looks fantastic. Other Baja plants such as Fairyduster (Calliandra californica) have done equally well.

This past weekend was the annual plant sale for the San Diego Chapter of CNPS. I pre-ordered a number of plants so that I wouldn't have to fight the crowd on sale day, and this worked out great. Of course, to do this you have to know what you want in advance. It might seem easier to just stroll through the plants on display and pick out whatever appeals to you. But that approach has led me astray in the past when I ended up with plants that ultimately died or performed poorly because they didn't really fit well with my garden. Pre-ordering forced me to really think about what plants I was interested in, research what conditions these plants require, and thus decide where I would plant them. While this is a lot more work upfront, it pays off in results.

Speaking of plant research, CNPS has a new website called Calscape which is a compendium of information about native plants for the garden. It brings together all the best info from books, other web sites, and personal knowledge of expert gardeners. Everyone should check it out.

Here's what I bought at the plant sale:

• Dutchman's Pipe (Aristolochia californica) - Although this attractive vine is native to the northern part of the state, it can do well here in the south with shade and some additional water.
• Indian Milkweed (Asclepias eriocarpa) - Milkweeds are the larval host plant for Monarch butterflies. I like this species because it is native to SD County and is rather showy.
• Summer Holly (Comarostaphylis diversifolia ssp. diversifolia) - I have a mature one of these already and I have a place for another one. This is a rare and beautiful plant.
• Lance-leaf Dudleya (Dudleya lanceolata) - I just can't get enough Dudleyas.
• Alkali Heath (Frankenia salina) - This little ground cover is found around lagoons and salt marsh. I have a spot for it next to my pond.
• Coast Goldenbush (Isocoma menziesii) - I didn't know about this plant prior to doing my research. Now that I know it, it's really perfectly suited for my garden.
• Laurel Sumac (Malosma laurina) - I should have planted this one 20 years ago but for some reason I didn't. Now I finally got one.
• Wild Cucumber (Marah macrocarpus) - I had one of these before that I started from seed. It ended up getting taken out when we remodeled our house in 2011 (see photo below). Since then I've been wanting another one.
• Western Sword Fern (Polystichum munitum) - I already have a couple of these in the shade garden on the north side of the house, but I always want more.
• Blue-eyed Grass (Sisyrinchium bellum) - Like I said, I always want more.
• Mission Manzanita (Xylococcus bicolor) - Like I said...more, more, more.

Okay, now here are some more pictures. First is a picture of the Marah macrocarpus that I had a few years ago. This species forms a huge tuber, and I had to dig up mine because of the remodel we were doing. At the time I dug it up, it was about 5 years old. It weighed about 25 lbs. and here's what it looked like.

Next, the new Summer Holly and the new Mission Manzanita in their new home. They are on the northwest corner of the house where the side yard starts to become the back yard. They will get some shade which will help when they are younger, but they will also get afternoon sun.

Next is the new Laurel Sumac in its new home. I put it in the planter on the southwest corner of the house in the Channel Islands section. It's tiny right now but it's a fast grower and should be up to the top of the fence in a couple of years. Although it is not an island endemic, it is found on Catalina and San Clemente Islands. I plan to shape it as a single trunk tree.

The last of the new plantings (so far) is the Alkali Heath. Although it is very tolerant of saline conditions, it doesn't require that. So it should do okay with a little extra water in this spot next to the pond, if the skunks and possums don't dig them up.

There are a couple of new residents in the garden. One is a big orb-weaving spider, perfect for Halloween. In this photo you can't see the web so it looks like the spider is just hanging in mid-air.

 

The other new resident is some bizarre kind of fungus. I haven't smelled it, but it must have an odor that attracts flies because they are all over it. And why would a fungus want to attract flies anyway? It's not like it needs to get pollinated. If anyone knows anything about this fungus, please let me know.