Sunday, December 6, 2015

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.

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