Wednesday, November 18, 2015

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.

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