The bulbs in the genus Calochortus have a well-deserved reputation for beauty and diversity. They also have a reputation for being difficult to grow, a reputation that is partially deserved. Most Calochortus species are not as adaptable as the Daffodils and gladiolus you can find in the local garden center. Even if you live in their natural range, they often won't persist more than a year if planted in the ground, unless you prepare the soil properly. In pots, they can be equally fussy. However, they are not impossible, and in fact once you understand their needs they are fairly predictable. And the spectacular flowers are worth the trouble.
The most extensive guide we've ever seen to Calochortus culture was created by Hugh McDonald of the Calochortus Society. In the 1980s and 1990s, he ran an extensive series of Calochortus-growing experiments in the east side of San Francisco Bay. His climate had cool winters with almost no frost, about 16 inches (42 cm) of rain in the winter, and mild summers with about five months of complete drought in most years. He summarized his results in the Society's newsletter, Mariposa. Unfortunately, the society is no longer active, but Hugh gave permission to reproduce his report here. It's below. It will give you a great start in growing Calochortus.
Keep in mind that if you follow Hugh's guidelines, you'll need to adapt your growing techniques to your local climate. Successful Calochortus growers typically experiment until they find the right combination of soil, sun, and water. For example, Jim Robinett, who grew California native bulbs very successfully for Robinett Bulb Farm, found that growing them in deep wooden boxes worked very well in his climate (Sebastopol, California). In his relatively damp climate, growing them in plastic pots often resulted in them rotting. Mary Sue Ittner has found that it is hard to keep the seed from damping off in her very wet humid winter climate. To avoid the need for fungicides, she starts seeds later in the winter than other growers, so they will germinate when the growing climate is much more to their liking. Since she lives in a relatively cool summer climate, she can keep them growing later in spring than growers in warmer areas. Meanwhile, Michael Mace, who gardens in warm/dry San Jose, CA, finds that plastic pots and fall sowing work well for many species, although the bulbs tend to dive deep in the pots and need to be repotted every couple of years as a result.
So start with this guide, tweak it for your conditions, and if you have problems, join the PBS e-mail list, where we'll be happy to answer questions.
Mariposa, Volume 2, #2. Copyright 1990, Hugh McDonald. Reprinted with his permission.
At the urging of some members, we will devote this issue entirely to horticulture. This is the beginning of the planting season for most spp., so it seems like a good time to list the best media for growing Calochortus, optimum watering schedules, planting depth, etc. Some of this will involve recapitulation of material printed earlier, but in this issue the material will be presented in a more compact and explicit format. It will also involve your editor going out on a limb and stating judgments and growing tips which may prove to be in error later. This is because the long term results of the growing trials which we discussed in V. II, #1 are not in yet. It may be that entirely unforeseen developments may force revision of much of what will be set forth here. Growers should keep this in mind as they read this growing guide, and use it with reservations. Local conditions should be given as much consideration as the incomplete and short term results we will use as a basis for this guide.
I. Media
In pots, the best mix has proven to be the U.C. Davis mix developed for general use. U.C. Davis recommends that it be used with fertilizer. This mix contains 1/2 sand, 1/2 milled sphagnum peat moss. The mix has proven superior for a wide range of spp. The related watering schedule is once a week, at 1/4" (.6 cm) planting depth. Those in climates with heavier rains (one inch [2.5 cm] or more times a week on average) might prefer a lighter mix yet, while those in drier climates might use a more humusy mix, to retain more water. It should be kept in mind that others have used quite different mixes successfully (see MARIPOSA V.I,#2-4 and V.II,#1 for C. Baccus', S. Farwig's, and J. Robinett's mixes. Farwig's mix is leaner than the U.C. Davis mix, while Baccus' and Robinett's are more humusy.)
[Editor's note: In later issues, Hugh recommended using 4 parts peat, 3 parts sand, and 1 part red lava rock when growing the Mexican summer-growing species. The people referred to above were some of the most notable Calochortus growers in California at the time. Their mixes:
- Charles Baccus: 2 parts medium fir bark, 2 parts ground forest humus, 1 part sand, and 1 part ground fir bark.
- Stan Farwig and Vic Gerard: 2 parts sand, 1 part topsoil, 1/2 part peat moss, and a handful of ground dolomite.
- Jim Robinett: 4 parts manureless commercial soil mix (he used Supersoil brand potting mix), 1 part peat moss, 1 part vermiculite, 1 part fine sand, and 1 part perlite.]
The second best mix was U.C. Davis soilless. This mix consists in 1/3 perlite, 1/3 vermiculite, and 1/3 sphagnum peat moss.
In the ground, the best results were obtained using clay soil, in which many of the spp. grow in the wild. Unless you live in the proper rainfall area, however, it might be better to mix in 50% organic matter to your soil. This can be redwood compost, fir bark, leaf mold or other common soil amendments.
II. Watering
The best watering schedule proved to be once a week, with qualifications. A one-day rainstorm counts as a watering. The amount used for watering from a can in non-rainy weeks was one inch (2.5 cm), applied at one time but not all at once. A watering can was used, and each pot or plot was watered in a consecutive sequence, so that the seedlings would not be deluged all at once.
A twice a week schedule proved to be too wet, while twice a month was too little. The qualification here is that the desert spp. did better if they were given a once a week schedule at first, until they are about 1" (2.4 cm) in height, and then watered less, viz twice a month. The desert spp. include C. aureus, C. bruneaunis, C. concolor, C. flexuosus, C. kennedyi, C. macrocarpus, and perhaps C. ambiguus, C. gunnsoni, C. nuttallii, and C. weedii as well. A few spp. receive more than one inch per week in the wild, particularly those from No. California and We. Oregon, but it should be kept in mind that for the most part these are xerophytic plants, which should be kept on the dry side. Also keep in mind that watering is proportional to drainage; a well drained mix requires slightly more water than a water retentive mix. Thus C. Baccus uses only rainfall to water his plants, by using a humusy, water-retentive mix.
All species should be kept dry during dormancy, although some receive occasional rains during dormancy. If it rains significantly in your area during the dormancy of an in-ground spp. it should be dug and stored. Otherwise the bulb may rot, especially under hot conditions. The bulbs may be stored in vermiculite or sand to avoid dessication. Seedlings should not be uprooted during their first year, thus growers in rainy climates are advised to start their seedlings in pots. By doing so they will be able to avoid having to dig up first year seedlings after dormancy. Bulbs grown in pots can be merely dried out: no digging or storage are necessary.
[Editor's note: Dry storage may mean very different things, depending on your climate. The soil in the pot needs to be fully dry, but you're not baking a cake -- the need is for dryness, not high temperature. In the relatively cool, humid UK, you may need to leave the pots in full sun, protected from rain, just to make sure the soil dries out. In the hot and dry parts of California, pots generally need to be unwatered in the shade; the local low humidity will dry them out nicely. There are a few exceptions, but many Calochortus are more vulnerable to summer moisture than bulbs from areas like South Africa and the Mediterranean, many of which are adapted to occasional summer rain.
There are also some differences in when you should start watering. Calochortus from mild-winter areas should be watered starting in the fall, as soon as the weather has cooled off. Species from inland cold-climate areas sometimes do better when stored dry until mid- to late-winter; they are used to being under snow at that time. Some cold-climate Calochortus bulbs may also need a period of dry or moist cold storage in mid-winter, to mimic winter conditions before they start to grow in spring. If you grow in a climate where you need to refrigerate Tulips, you may need to do the same with the cold-climate Calochortus.]
III. Shade and Sun
The fairy lanterns and pussy ears prefer shade. All the others prefer part shade, especially if the lower part of the plant is in shade and the upper part is in sun. In very hot climates, full shade during the hottest parts of the day may be advisable, with part shade during the early morning and late afternoon. Areas with frequent fog, overcast, clouds or rain may do better with full sun at all times.
IV. Fertilizer
I just started using Lilly-Miller "Bulb & Bloom", a complete, low-nitrogen bulb fertilizer, this year. Results are impressive with regard to both seedling growth and flower quantity and size. Others use ammonium nitrate (Baccus), superphosphate (Kline), "Miracle-Gro" (Robinett), and dolomitic limestone (Farwig). I use one teaspoon per 5 gal. (20 liter) pot, or per square foot of ground. In the trials so far, "Miracle Gro," a commercial fertilizer, proved as effective as the bulb fertilizer.
[Editor's note: McDonald says the addition of fertilizer is essential if you're using one of the soilless mixes. He feels he didn't emphasize that enough in the original article. The Lily Miller fertilizer mentioned in his article was a granulated, inorganic bulb fertilizer (about 4-10-10), with added micronutrients. Unfortunately, the fertilizer was reformulated in the 2000s to be based on "natural" materials such as poultry waste, which may promote rot in potted bulbs.]
V. Pesticides
Fungicides have proven safe for seedlings (Ortho "Captan" and Lilly-Miller Soil and Bulb Dust). A small amount may be mixed in the top of the mix or soil to aid in the prevention of damping-off. Follow package directions, and be sure the fungicide is specific to damping-off pathogens. An alternative is pasteurization of the media by baking it at 180 degrees Fahrenheit (80 °C) for 2 hours.
VI. Planting Depth
As we indicated last edition, the best planting depth proved to be 1/4" (.6 cm) for seedlings of all spp. Next best is 1/2" (1.2 cm). Again, it should be noted that other growers have quite successfully used other planting depths. Specifically, Jim Robinett places his seed 3/4" (1.8 cm) below the surface.
For bulbs, 3-4" (7.5-10 cm) is adequate. Except for the pussy ears, a large pot should be used--at least one gallon (4 liters) for three bulbs. These larger pots allow for more support for the taller spp., especially the Mariposas. A 3- or 5-gallon (12-20 liters) pot is even better.
VII. Spacing
Bulbs prefer 3-4" (7.5-10 cm) apart, but will tolerate less if given enough fertilizer. Seedlings tolerate 1/2-1" (1.2-2.5 cm), but will eventually need more space.
VIII. Planting Time
There does seem to be some genetic code in Calochorti which inclines them to germinate at the optimum time of year for rainfall in their indigenous areas. Thus the Calif. spp. germinate in fall or winter, during the rainy season on the Pacific Coast; while the Mexican spp. germinate in early summer, the season of rainfall on the Mexican plateau.
It is difficult to judge when is the optimum planting time for the different spp., then, unless one lives in or near their indigenous zone. In general, the Pacific Coast spp. are best planted in late autumn, the inland US/Canada spp. in very early spring, and the Mexican plateau spp. in late spring to early summer.
Exceptions are for growing spp. under conditions which are severe or unusual for a particular spp. Most Pacific Coast spp. require a degree of chilling to germinate, and cool conditions for optimum growth. The exceptions are certain So. Cal. coastal spp., which grow in mild conditions year round. As these spp. do not require chilling, but will not take cold, they can be planted in spring in cold climates (C. weedii, C. plummerae, and C. catalinae). Other winter growing spp. should be planted in late winter or very early in the spring in severely cold climates, in order to prevent growth until spring.
If your area is on the dry side in winter, the inland spp. can be planted in the late fall, provided it is not a mild climate. (Growers in mild climates must cold stratify the seeds of many inland spp. to get them to germinate--see sect. below on cold stratification.) These inland or high altitude spp. include C. apiculatus, C. elegans, C. lyallii, C. subalpinus, C. nudus, C. minimus, C. nitidus, C. eurycarpus, C. Greenei, C. Howellii, C. longebarbatus, C. persistens, C. bruneaunis, C. palmerae, C. leichtlinii, C. macrocarpus C. aureus, C. invenustus, C. kennedyi var. munz, C. nuttallii, and C. gunnisoni. Some of the SW high altitude spp. may do better with some cold stratification as well (C. flexuosus, C. concolor, C. kennedyi, and C. ambiguus).
The Mexican spp., with the exception of those from Baja, require summer germination and watering (June to the end of October). Depending upon the altitude at which they were collected, they prefer dry winters with cool to cold temperatures.
With the exception of the Mexican spp., almost all of the Calochorti can be planted out of season, so long as some attention is paid to their optimum growing conditions. As most of the growth is in spring, cool temperatures are requisite. It is quite difficult to grow any of the inland US/Canada spp. or the Pacific Coast spp. (with the exception of the So. California spp. discussed above) in hot weather. But the spring growers can be started in fall in mild climates, provided they are first cold stratified. And the winter growing Pacific Coast spp. can be started in spring if they are kept sufficiently cool.
IX. Vegetative Propagation
The only known method of vegetative propagation for Calochorti is bulbifery and bulbilifery. So far as is known, all Calochortus bulbs divide slowly, over time. Certain spp. also produce bulbils, small bulblets, in the leaf axils (where the leaf meets the stem). These spp. are C. uniflorus, C. longebarbatus, C. umbellatus (rarely), all of section Mariposa except for C. dunnii and C. striatus, (rarely for several spp.), C. ghiesbreghtii (rarely), C. barbatus (rarely), C. spatulatus, C. pringlei, C. cernuus, C. purpureus, C. foliosus, and C. hartwegi (rarely).
It is not known, at present, whether other vegetative propagation techniques used with other genuses of bulbs will work with Calochorti.
X. Cold Stratification of Cold Climate Seeds
Seeds of spp. from cold climates require chilling under moist conditions to germinate. In their native range this is provided by melting snow. In mild climates, it must be provided artificially, by simulating melting snow. It should be noted that mere cold is not enough: both cold and moisture must be present (per field trials). Providing an atmosphere which hovers around 32 °F (0 °C) during moist stratification of seeds will achieve good results. Either one can place the entire pot in a(n old) refrigerator, keeping it covered with ice as it slowly melts; or the seeds can be put in moistened vermiculite in a ziploc bag, and transplanted when they germinate. This process usually takes about six weeks, but some of the seeds may take longer.
XI. Seedling Care
The most difficult stage of growth for Calochorti is the seedling stage. We have treated seed care under most of the above headings, but here are some additional tips:
1. It is better to start the seedlings in pots or flats and transplant them to the soil after their second year of growth, unless one lives in or near the native range of asp.
2. Bottom watering of pots will reduce the danger of seeds floating about, or becoming dislodged during the germination period. Some growers place a top dressing of tiny pebbles or bark pieces on top of the soil or mix to hold the seeds in place during watering and keep the moisture even. As a bonus, the top layer insulates against excessive heat or cold.
3. The seeds must be kept evenly moist, but not sopping wet. This applies especially to the desert spp., which can be particularly finicky as to water. Too much water encourages damping off, which can carry off half or more of the seedlings, or cause the tiny bulbs to rot. Too little water can cause dessication.
4. Warmer, drier climates may require somewhat more water; cloudier or cooler climates somewhat less, and so on. The seedlings should be checked every 4-5 days for moisture; especially potted ones. It is advisable to let them dry off a bit between waterings both to discourage damping-off and to increase aeration, but not more than a week should elapse between waterings or rain (except for the desert spp. as above).
5. Enough water should be applied to keep the water table below the roots, and thus prevent salt build-up. Thus enough water should be applied to flush any excess salts (fertilizer) from the root zone, but no more: a trickle should appear out of the pot's drain holes after watering.
6. Dormancy will vary by sp., but it is generally summer to mid-autumn for the winter (Pacific Coast) spp., mid-summer to late winter for the inland and high altitude spp., and late autumn to spring for the Mexican plateau spp. The bulbs should be kept as dry as possible during this period. Dormancy is marked by a browning of the tiny first year leaf, and then its withering.
XII. Greenhouse Culture
Cold climate growers can simulate native conditions for mild climate spp. through the use of an alpine house, an unheated greenhouse. Most Pacific Coast spp. prefer cool, but not frigid winters. In the hilly or mountainous areas where most of them grow, they are specialists in surviving where the nights dip below freezing, but the days warm up to above freezing. This is what an alpine house can provide: warm days, but cool-cold nights.
Only a few sp. will tolerate a heated greenhouse, viz., the So. California coastal spp. This holds especially if the greenhouse is kept humid. Most spp. prefer cool growing conditions. An alpine house can also be used to keep desert spp. on the dry side, and dormant spp. out of the rain.
I have no experience of forcing, but there is one source on the subject (to be printed in the Jan. 1991 Mariposa. Also cf. the section on out of season planting above, sect. VIII).
XIII. Pests
Apart from damping-off, discussed above (sect. V), Calochorti are relatively pest-free. There may be the occasional rodent or gopher, but these can be kept away with Felis domestica. Near the coast mildew (botrytis) has been reported, but I've never encountered it. Proper drainage as well as thorough drying between waterings may prevent it. The occasional aphid can be checked with ladybugs. Snails and slugs must be watched for.
XIV. Calochorti for Specific Climates
1. Mild, moist climates: C. albus, C. amabilis, C. amoenus, C. pulchellus, C. monophyllus, C. tolmiei, C. umbellatus, C. uniflorus, C. catalinae, C. palmerae, C. splendens, C. venustus, C. superbus, C. vestae, C. luteus, C. simulans, C. clavatus, C. plummerae, C. weedii, C. obispoensis, C. fuscus, C. ghiesbreghtii, C. barbatus, C. spatulatus, C. pringlei, C. cernuus, C. purpureus, C. hartwegii.
2. Mild, dry climates: C. albus, C. catalinae, C. flexuosus, C. dunnii, C. splendens, C. striatus, C. venustus, C. concolor, C. kennedyi, C. clavatus, C. ambiguus, C. plummerae, C. weedii, C. barbatus, C. spatulatus, C. pringlei, and the other Mexican cyclobothras, if they are kept moist in summer and dry in winter.
3. Cold, dry climates: C. elegans, C. longebarbatus, C. nitidus, C. eurycarpus, C. flexuosus, C. leichtlinii, C. macrocarpus, C. nuttallii, C. kennedyi (var. munzii), C. ambiguus, C. gunnisoni, C. aureus, C. bruneaunis, and the higher elevation Mexican spp. e. g. C. venustulus, and high altitude strains of C. barbatus.
4. Cold, moist climates: C. albus (Sierra form), C. apiculatus, C. coeruleus, C. elegans, C. lyallii, C. subalpinus, C. minimus, C. nudus, C. nitidus, C. greenei, C. howellii, C. persistens, C. palmerae, C. superbus, C. vestae, C. luteus, C. leichtlinii, C. invenustus.
With protection, one can grow the Mexican spp. in cold climates as well. Simply dry them out in late autumn, and store them in a cool place, which will not freeze
Here are links to some other articles that discuss Calochortus culture:
Growing high-elevation (cold winter) Calochortus
More from Hugh McDonald
Charles Baccus on growing California native bulbs