One little-considered candidate for drought tolerant ornamental horticulture is alfalfa. It has a deep root system, fixes its own nitrogen and is native to relatively dry climates in Central Asia.

It isn't hugely ornamental, but the flowers are attractive and the growth habit is at least somewhat adaptable to circumstance. It can be mowed, though not shorter than a few inches, and isn't traffic tolerant (nor texture-appropriate) for playing surfaces. Given a need for minimal inputs it's far from the worst thing that will grow in an otherwise-empty space.

Alfalfa is thought of as a water-intensive plant, but that is only an artifact of industrial agriculture. Yes, for highest possible yields per harvest, it has to be watered heavily. If its only job is to please the eye and displace opportunistic weeds, very little water is needed. Some claim 15 inches per year is sufficient.

There are a few caveats: First, it doesn't form a dense enough canopy on its own to preclude weeds invading. Alfalfa is self- toxic, at least when grown from seed, and the commercial stands that look utterly dense viewed from the ground are actually rather sparse compared to a typical lawn. Alfalfa works best is a mixed population of plants.

Second, because it's universally liked by everything that creeps, slithers or crawls, it is very subject to getting eaten. Sprouts are especially delectable, and starting from seed has proven more or less impossible in an established surburban yard without chemicals. Once plants are a few inches high the pest problems diminish greatly. Ahids can be a problem, though controlled by selective cutting and predator (ladybug) encouragement.

Third, commercial agriculture readily accepts delicacy of maintenance in exchange for high yields. Commercial "production" alfalfa types are therefore ill-suited to decorative applications. "Grazing" types, adapted to minimal cultivation and tolerant of trampling by livestock offer a somewhat better choice. Still, my luck in starting seed in a typical-sized suburban yard met with little success, mostly because of pest damage supported by wet conditions in neighboring yards.

It happens that the Sacramento Valley has been home to alfalfa since roughly 1850 and a small number of plants have gone feral, growing along roadsides near commercial fields. Since they were already more or less adapted to the climate, diseases and pests the local feral plants seemed like good candidates for ornamental use.

Collecting seed from these plants is tedious, but taking cuttings is easy. The technique described below is from: https://stockingerlab.osu.edu/sites/stockinger/files/imce/PDFs/Protocols/AlfalfaVegetativePropagationByStemCuttings.pdf A local copy of the same file is here.

The cuttings can be started direct in the soil with a roughly 50% success rate, or in pots to be transplanted later. Cuttings are prepared by starting with a vigorously growing stem with 5 or 6 nodes. The stem is trimmed a few mm from the bottom node, and all leaves are likewise trimmed save the uppermost node. The terminal bud is removed to prevent, or at least delay, any attempt to bloom early.

The lowest node is coated in indole-butyric-acid rooting hormone and the stem slipped into a slender hole poked in the ground or in a potting medium. The medium must be kept moist for about two weeks, so one has to trade off the relative convenience of planting directly or transplanting (needing much more digging) the growing plants. It's important to keep the remaining leaf at least a few inches above the rooting medium, to discourage pests like pillbugs.

Attempts to use unconvential rooting media (rolls of newsprint, water) generally failed unless done in the spring. At this point I'm inclined to think that given a month or two of suitable weather direct planting of prepared stems outdoors is probably the most labor-efficient approach given that no real digging is needed, just a pencil-sized hole in the ground. If it's too hot, dry or cold to start directly then use of pots under a shelter or greenhouse followed by transplanting is worthwhile.

When the weather is hot keeping the cuttings from drying out can be difficult. One promising approach is use of a quart yogurt cup with a cover in place of an open pot. The bottom is given drain holes and filled 1/3rd with potting soil. A short cutting is placed in the soil as usual and the lid snapped on. It looks as if the cover retards water loss to allow a couple days between waterings. The small volume of rooting medium implies an early plant-out. That might be a problem if plants need to be largeish before planting out, as when insect pressure is high.

There will be some post-transplant mortality, but not very much. Perhaps 10%, attributable, I think, to disease. Given the work of digging required, a 50% loss of starts placed in pierced holes is a near-wash in effort. But that assumes suitable weather. The odds of success at rooting in-ground are near zero in hot weather.

Once planted out the alfalfa has to be treated like any other bedding plant until it establishes an adequate root system. In my case that required several months of regular watering.

The growth habit of alfalfa varies widely. Some plants are low and compact, others sprawl for meters. None that I've seen, even the so-called "creeping" types, root from their stems. They all seem to sprawl, bloom and then to drop seed directly below flowers, which germinate where they land. From this it seems unlikely alfalfa will become obnoxiously invasive, at least in a Mediterranean climate. The minimum spacing among plants growing along roadsides is usually a foot or so, often much more. This is a stark contrast to the other famous Eurasian import, star thistle.

If one desires a self-reseeding stand it's mandatory to establish plants from a wide range of donor specimens. Alfalfa is an obligate outcrosser, so genetic bottlenecks are particulary destructive. On the other hand, if there's fear of a planting becoming invasive (in my experience not a credible hazard) limiting oneself to a single donor will largely eliminate the risk.

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