Bulbs are often one of the most conspicuously absent elements in a native garden: geophytes (bulbs, corms, tubers). While some species can colonize and make impressive displays in time, most bulbs are better used as accents or highlights in the garden. Flowering time for a given species is often brief and so inter-planting with other plants, especially annuals, allows native bulbs to be more effectively used. Both the bulbs and seeds of re-seeding annuals require a dry summer and so are good companions. Below are general guidelines for planting and caring for your bulbs.
In the Garden or in Containers?
In either situation it must be remembered that nearly all California native geophytes require a dry rest period in summer. Among established plantings of perennials (especially grasses) and smaller shrubs that receive no watering or only occasional light watering during summer, Brodiaea, Triteleia, Dichelostemma and Calochortus can be inter-mixed. The two main drawbacks to planting these bulbs in the open garden are a) over-watering in summer, which can rot the bulbs, and b) getting lost amongst larger plants. In the latter case, too much shade may be cast by shrubs or larger perennials, thus resulting in bulbs that are too weak to flower, or the show of flowers can be drowned out by surrounding plants. However, smaller companion plants (1-2 feet tall), from annuals to shrubs, provide some protection from disturbance and support for the flowering stems. Exciting color combinations can also be achieved in this way. Half day sun, preferably morning sun, is ideal for a majority of native bulbs. Many native bulbs are well-adapted to heavy soils and do not need organic amendments. Where raised beds or a slope can be provided, native bulbs will be even happier.
In containers the grower has better control of various factors including soil, watering, light exposure and protection from rodents. Plants in pots are portable and can be moved for enjoyment indoors (briefly) or other sites outdoors. Though many native bulbs can be successfully grown in smaller containers it is generally best to use larger pots, at least 8” deep, for groupings of several bulbs together. A sandy soil mix is suitable for most species. This can be obtained by mixing together approximately 40 percent packaged potting soil for container plants, 40 percent river or concrete sand and 20 percent garden soil (loam). Once the leaves appear allow the surface of the soil to become dry before watering again. In containers, moderate feeding with any commonly available liquid fertilizer is beneficial while the plants are actively growing. Since containerized bulbs should only need re-potting every third year or so, slower-releasing nutrient additives such as bone meal and blood meal are also useful.
How do I Plant my Bulbs?
As a general rule, bulbs in the garden and in containers should be planted as soon as weather cools in the fall (Oct.-Nov.). Plant to a depth approximately three times the length or width of the bulb, whichever is greater. For en masse effect, do not plant closer than about one inch apart. These rules of thumb can be used to gauge how many bulbs can be planted in a single container and also for informal groupings in the garden. Bulbs should be watered-in the same day they are planted and then left to sit until the first rains. If the bulbs sprout as a result of this first watering, before the rains, water weekly or when dry until rains arrive.
What about Maintenance?
In general, our native geophytes are long-lived and if they perform well for you in their first year they can be depended upon to brighten your garden for many years to come. They will not burn-out like many other commonly sold bulbs such as tulips and crocus (most varieties) and other cold-winter species. Varieties in the Brodiaea alliance (Dichelostemma, Triteleia, Brodiaea) are good for naturalizing and will slowly multiply and make clumps or patches over the years. If seed capsules appear they can be harvested and the seed is then planted in the fall. Seed-grown bulbs may be planted-out after about three seasons of growth. Bulbs that have multiplied naturally in the garden can be dug in summer and separated to provide material to plant in other locations.
What about Calochortus?
The mariposa lilies are more challenging to grow and the reward is correspondingly greater, with elegant goblets or globes of white, yellow, pink and other basic colors. Inside the flower are striking patterns of darker colors and complex arrangements of hairs. Recommended for those with some experience growing native bulbs or other dry-climate geophytes. Basic requirements are a sunny position in pots or in the garden and a freely draining soil mix with low amounts of organic matter. A very sandy soil mix is a good starting point, with the addition of pumice (for drainage) and including only a minor component (about 10-15 percent) of organic material such as bagged potting mix for container plants. Once planted in fall the bulbs may take quite a while to sprout, as late as January in some cases. Try to avoid watering as much as possible and let the rain do the work. Do not keep the plants out of the rain! During the growing season a few applications of low-strength orchid fertilizer (high in nitrates, low in ammonia or urea) are beneficial. Keep pots or beds completely dry once the leaves have turned mostly yellow. Greatest success can be expected in containers and in raised beds. Wooden containers (1’ x 1’ x 1’) are good for mariposa lilies and other bulbs. Transplanting should be needed only occasionally, every 3-4 years, since the lean soil mix will not degrade very much over this time.