Friday, June 9, 2017

Growing sand-verbenas (Abronia/Tripterocalyx)

For awhile, I've been working on plant defense and other aspects of the ecology of the sand-verbenas (here and here). Despite being much-beloved coastal and desert wildflowers, Abronia species have a (slightly deserved) reputation for being hard to germinate, hard to keep alive, and just generally not that great plants. Thus, they are uncommon in gardens of even the most diehard native plant folks.

Abronia villosa, Imperial Dunes, 3/2017. 
For the past two years, I've been growing them in the lab, greenhouse, and home garden  and refining my protocols for growing them. I haven't taken a really scientific approach to this - I haven't done huge numbers of replicates or really controlled environments, but I've tried out a number of approaches, talked to lots of more knowledgeable folks, and tried quite a number of species with success.

Abronia maritima, the easiest species to clone and perhaps the easiest to grow in captivity. Morro Bay, 4/2016. 
The keys to success are actually quite simple - (1) they need sand, (2) they need space, (3) if you want flowers, they need fertilizer.

(1) Most sand-verbenas are restricted to very sandy areas - coastal dunes, desert dunes, desert washes, etc. so its definitely no surprise they need sand. For bigger plants, I use ~75% play sand - the cheapest at ACE - and ~25% potting soil (I've been using Sunmix with good success). I've tried 50/50 and some species (such as fragrans), do like this, but the sandier coastal and desert ones seem to like more sand. Sand is really well-draining, so you needn't worry about overwatering, but it does lose its moisture really fast, especially if the plant is too large for the pot, so keep an eye on them. I water every 3-4 days in the lab and greenhouse.

For seedlings, I use closer to 50/50 and keep them covered to retain moisture. They dry out very quickly and it takes them awhile to really get going (much longer than most of your garden plants).

I tried transplanting some into the clay soils of Davis. Unsurprisingly, they all died very quickly. I bet you could do them in turface, cactus mix or perlite or maybe even coarse vermiculite, but sand is proven and it is so cheap and easy, I don't feel much need to change that.

Abronia pogonantha in the lab. You can see the flowerbuds just starting on this one. 

(2) Keep them in big pots. This is really important - Abronia usually have really extensive root systems to find whatever little nutrients and water are in their sandy environments. The picture below demonstrates this very clearly.

The root system of Abronia latifolia in a blown-out dune at Doran Beach, Sonoma, CA. 
The desert species - villosa, pogonantha, turbinata - can get away with being in small pots - but if so, do use the really deep ones. However, since they are all sprawling, prostrate groundcover, they look and do best if given space above-ground, too. I transplant them to 8" or 10" pots when they have 2-4 leaves. This allows them to develop a good root system fairly quickly and seems to lead to quicker growth and flowering. On my patio at home, I have villosa and fragrans in 5 gallon buckets (with holes drilled in the bottom) and a ~10 gallon planter. Both of these have ~75/25 sand and work well (and buckets are cheap and easy).

Abronia ameliae in a 4" pot. This plant desperately needs transplanting. 

(3) Fertilize constantly. Sand (and the nonnutritive potting soil I generally use) is pretty much nutrient-free. This seems to not matter much for vegetative growth, but for most of the species, I get flowers only when I fertilize often (1/week or more!). The annual species seem to flower with a bit less pushing, but the maritime species, especially umbellata and maritima, need to be given a little push. With regular fertilization, warm temperatures and longer days (15 hours or so), they will flower constantly - I have fragrans, umbellata, and villosa that have flowered for over a year without stopping.

The long-lived and long-flowering umbellata individual. Cloned from field-collected tissue in SLO county. 
Germination. I'd written a post before on germination, but I won't even link to it, as my germination protocol has gotten much better. Here's how I do it now. You'll need ethephon (I use Monterey Florel Brand Growth Regulator, available online or at Home Depot) and some sterile media - I use vermiculite, but paper towels work, too and tupperware or a petri dish.

Papery fruit (=anthocarps) of Abronia latifolia

(1) Remove seeds from the papery fruit. Note that many of the fruit may be empty or have inviable seeds. I'm not sure what causes this, but its likely pollination failure.

(2) Mix a solution of ethephon. For the Monterey hormone, I use .66mL per 1L of water (distilled is preferred).

(3) Place seeds on vermiculite or wet paper towel in your container, moisten heavily (but don't wet - there shouldn't be standing water) with your mixture. Leave for a few days in a cool dark place. If you get lucky, it will look like this after a couple days. Leave them for a day or two more, until you see the roots starting to get fuzzy and elongating (>1 cm, at least).

Germinating Tripterocalyx micrantha seeds. 
(4) Transplant into a 50/50 sand/sterile soil mixture, well-moistened (but not wet), which is covered to keep the humidity up. They will grow painfully slowly. But, eventually they will get a hold on life and put on a few leaves. At that point, transplant to a larger pot and bear in mind the tips above.

Seedlings (of hybrid turbinata x pogonantha). Notice that they have one seed leaf - these are derived dicots, not monocots as it might be tempting to assume!
Growing from cuttings.

I've had alright success with cloning plants and some folks at the botanical conservatory here are doing a little more systematic attempt at figuring out how to clone them. I was using low-strength rooting hormone (1%), cutting below a node, and putting them in sand/perlite. I was getting low success, but importantly, not no success. A. maritima and fragrans were the species most amenable to this - I've had mixed luck with others (turbinata/umbellata/ breviflora) and complete failure with latifolia and villosa. The successful ones took a really long time to root - 4-6 weeks - but once rooted were quite happy and as easy to care for as others.

Hopefully I'll have an update on this soon.

A. umbellata umbellata (left) and A. latifolia (right). Morro Bay, 5/2017.

Other various tips:

I cage my plants with chicken wire to keep them somewhat contained. Tillett (1967) says that he trained his up poles in a greenhouse. I've had no luck with this, but the chicken wire cages work pretty well. I either route the stems coming out back in, or just trim them off. This seems to work well to conserve space.

From left to right: A. umbellata breviflora (pink), maritima (behind, upright, no flowers), Tripterocalyx micrantha (in front, drooping), latifolia (behind, dark green leaves), turbinata (white flowers), umbellata umbellata (purple, far right)

Crossing is pretty easy. Since most species (A. u. breviflora, all Tripterocalyx spp., and A. ammophila excepted) are self-incompatible, you don't generally need to emasculate. Find out where the stigma comes up in the tube, and cut the flower between that and the lowest anther, open up the tub so the stigma is exposed, and pollinate! I've had good luck with intra- and inter-specific crosses.

Hybrid pogonantha x maritima

If you have any comments or questions, do let me know! I'd be really excited to help folks out who want to try them.