A NON-CONCISE GUIDE TO THE CULTIVATION OF BULBS
"What is the answer? ... what is the question?" dying words attributed to Gertrude Stein
"The more I grow, the less I know." frequent muttering of the author
[Unless otherwise indicated, this discussion reluctantly uses the term "bulb" in the imprecise, but generally accepted horticultural sense as including such diverse structures as corms, rhizomes, tubers etc.]
If dying words are cherished for a possible last insight into the human condition or as the distillation of a lifetime's experience, those of Miss Stein's display a simple wisdom, as well as the requisite poignancy, that causes me to wonder if, given all the other matters to claim one's attention at such a moment, she hadn't been saving them up for just the right occasion.
Their wisdom and poignancy is apparent if one considers, for instance, a misspent youth when one had all the answers, but as it often turns out, to all the wrong questions. Or a gardener who has followed expert advice to the letter in anticipation of a blooming wonder and is faced instead with a desolation. While the expert may or may not have furnished the right answers, it seems likely that not all the right questions were posed.
A further relevance the quotation has to the topic at hand concerns a certain shame I feel upon occasionally being billed by kind people as an expert in the cultivation of bulbs. While I may not demur at the time ... after all it usually happens when I'm being introduced as a speaker, often by the person who invited me, and calling into question the judgement that issued the invitation would be rude... I do feel a participant in a fraud. I certainly don't feel as I always imagined an expert should feel before I was elevated to that rank myself.
An expert should possess arcane knowledge, be fully in command of his field, self possessed and usually, if not always, ready with the right answers. Instead of right answers I find myself still fumbling to come up with the right questions.
In practice, I pot up bulbs or seeds and tend them in accordance with practices that are common knowledge and hope for the best. If less than the best is achieved, most folks will never know. If the best happens often enough, one becomes an expert.
I do from time to time think about what's going on with the bulbs in my charge and ponder what I'm attempting to do with them. It's inescapable. About the only question that will be addressed here with any degree of adequacy is: "What do you think about when you think about cultivating bulbs?"
These comments will focus on bulbs for which there is no well established literature, and the best guide to the cultivation of these is gained from what knowledge may be culled of their habitat. This can be a task second in difficulty only to that of obtaining the bulbs themselves. It is not a task undertaken in any attempt to duplicate the habitat's features, but rather to extrapolate the bulb's needs. These needs are usually less than the totality of those features, and at times considerably so. This introduces an irksome aspect of such research: when all the data available is assembled instead of the answers sought, one may flounder on ambiguities, for a question presents itself: Which of the many factors that constitutes the plant's native environment does the plant require and which does it merely tolerate?
The answer to this will require some speculation and experimentation based on the data gathered.
When the description of two species of South African Romulea characterizes them as "aquatic" and notes they are only found submerged in seasonal pools and never on the adjacent ground, it may be assumed that an important horticultural requirement has been identified. But when one reads further that they perform as any other plant in containers under normal cultivation, it becomes obvious what has been reamed is of geological rather than horticultural interest: the native soil of these Romulea is of a dense "hard-pan" clay that is poor in absorption of water and, as a consequence, pools are formed that persist throughout the rainy season. The Romulea grow where the only source of moisture is available. It is cautionary though to consider that these two species may be less tolerant of periods of drying out during growth than other related species.
Rainfall figures for the bulb's habitat can certainly be a useful guide to its watering needs, but they are far from infallible since other sources of moisture may be available. This is most obvious in species that occur along rivers or in seeps formed by underground springs or on beaches within the reach of tides. Often these will be evergreen, or nearly so. Other sources are less obvious.
Learning that a bulb is from a high elevation suggests that it is subjected to a wider range of diurnal fluctuation in temperatures than low land bulbs. Such wide divergence in daily temperatures are often productive of dew.
Certain species of Cacti from the Atacama desert of Chile such as Copiapoa provide another instructive example. For some years Copiapoa had a reputation of being excessively difficult in cultivation. This resulted from its cultivation being formulated on partial knowledge of its habitat. The Atacama, one of the harshest deserts in the world, normally receives less than a inch of rain in a year. Consequently, water was doled out by the thimbleful, the plants monthly declined and eventually keeled over with their reputation intact... until some brave soul dared water them very much as other cactus and Copiapoa thrived. What had been overlooked was that such cactus, as well as many bulbs, are largely coastal plants and the coast of the Atacama is subjected to regular fogs.
The top of Table Mountain at Cape Town in South Africa is often cloaked in fog, picturesquely known as its "tablecloth". This is not only a source of additional moisture for the plants there, but also acts as a screen against the drying effects of sunlight experienced by plants on the lower slopes.
Even so seemingly elementary a finding as whether a plant occurs naturally in sun or shade does not yield an immutable precept for its situation, for we have found that while shade dwellers are not generally accepting of increased sunlight, many bulbs that commonly are found in full sun will tolerate and even appreciate shade.
Probably the most crucial and easily assessable information derived from the plant's habitat is whether winter or summer is its season of growth. It comes as no revelation that winter growers are usually from areas of a "Mediterranean climate": all or most of the rain falls in the winter months. But this is not invariable.
South American bulbs can present a dilemma in this connection, for some come from areas of year round rain but insist on winter growth. The explanation provided by a most knowledgeable Argentinean horticulturist is that while the habitat of theses winter-growers does receive precipitation in all seasons, perhaps daily, in summer, the heat is such that evaporation takes place very quickly and it is only when the cooler temperatures of winter arrive that the ground is saturated to the depth of the rootstock. (This may also indicate a need for a higher humidity than that required by bulbs from other areas of the world to prevent desiccation of the bulb when it is dormant ...but this is merely speculation, not established fact.)
The question may arise: "Well, wouldn't it be advisable then to convert such bulbs to summer growth here by providing them with regular drenching?" Well--- it might be worth a try, but there is a very good chance it wouldn't work. I say this because such a procedure ignores the bulb's metabolism, that complicated series of chemical changes that regulate all vital functions in living organisms. This is an aspect of horticulture I certainly don't know a whole lot about and don't even know how much is known. But one does well to always be aware that this is the fundamental process we are attempting to effect by the application of all techniques of horticulture, and a bulb's metabolism involves an intricate association between temperature, moisture and evolution.
Temperature seems to be the controlling factor in initiating the start and end of growth for at least a number of bulbs. This is a conclusion reached after observing such things as the emergence in autumn of roots and stems on winter-growing bulbs that have had no water as yet, as well as the sudden cessation of growth with an unseasonably hot spell even though moisture is still available. But this effect of temperature is intimately involved with watering, for the metabolism of the plant that regulates growth appears to have evolved in response to temperature gradients that are associated with seasons of optimal rainfall to insure a full cycle of growth as well as the seasons of drought and dormancy.
In the case of these South American bulbs, evolving in an area where moisture was only available to the root stock in cooler temperatures resulted in their requiring coolness for the necessary metabolic processes involved with growth to begin.
There are a number of ramifications to this association of temperature, moisture and evolution for bulb culture.
In colder climates, one might wish to delay the start of growth in tropical or semitropical bulbs until late winter/early spring for more favorable growing conditions, but they may insist on appearing with the first cool nights of autumn demanding water and requiring prayers.
Although I know of none from the southern hemisphere, bulbs from regions that are covered with snow or experience drought during winter require a prolonged dry cold spell before receiving moisture. This information is exploited in the destruction of bulb plants by the self-indulgent practice known as "forcing", a procedure quite unrelated to horticulture.
Day length is often mentioned in connection with plant growth, and its influence on flowering is commonly employed in floriculture. While the function of light in photosynthesis is obvious in plants that have stems and leaves above ground, it may have a more subtle effect on both active and dormant bulbs. Longer hours of daylight not only increase but also prolong elevated soil temperatures, providing a more uniform condition throughout a twenty-four hour period. Some summer-growing bulbs may do best not only with higher temperatures, but also with this more uniform soil condition, and resting bulbs may best complete their dormant cycle with it. Conversely, I believe there is evidence that many winter growing bulbs may require wide diurnal variations in temperature, most obviously, but not exclusively, those from desert areas or higher altitudes.
And this association also involves a question most seriously in need of in-depth research: whether or not a bulb is tolerant of moisture during dormancy. While many are indifferent to watering during their resting periods, others will quickly rot if subjected to it. I have read that those susceptible lack a defense against pathogens that require both heat and moisture. Although the actual pathogens were not named, experience would support the assertion, and it is evident that winter-growing bulbs are most at risk. It would be helpful if the factors which impart immunity to some bulbs could be isolated and possibly supplied to those less fortunate. In any case, in the absence of definitive information, the wisest course is to provide all dormant bulbs with drought conditions.
I am only too aware that the comments so far are woefully imprecise for those desiring specific recommendations. The general requirements for bulb culture are readily available, as are the more specific requirements of bulbs that are readily available. But even with plants with some history of cultivation there are at least two problems with precise recommendations.
First, neat and specific directions tend to lull a capacity for speculation, and it should be apparent by now that I consider speculation an essential process in horticulture.
Secondly, such recommendations are based on the experiences of the writer in his own particular area, and this can be quite different from one's own. I am always discomforted by a frequent assertion in English texts that bulbs require "a thorough baking in summer"... 350 degrees for forty minutes?... This may be sage advice for an English summer, but not necessarily elsewhere.
While the vicissitudes of plants in an environment that is alien to them are certainly instructive, such information often requires much the same speculation and evaluation as habitat information, which remains a requisite for the correction and confirmation of any conclusions reached.
I hope it will be helpful to offer an example of an attempt to gain more comprehensive insight into the cultivation of a species through speculation on data from diverse sources. It is a species we have had good success with, and this success has several times occasioned surprise. Such surprise often lends a mystique to success and this can contribute to the charge that we are experts. But a little reflection on the source of this success makes it obvious that there was really no reason for surprise, no mystique adheres to it, no expertise was involved.
Some years ago a kind horticulturist in Oakland, California gave us two bulbs of the rare and beautiful South African plant, Daubenya aurea. I had phoned him hoping that seed might be available. He reported that the species flowered only intermittently for him and had never set seed, so the best he could do was to provide bulbs.
In our location at Concord, California the species flowers every year and sets seed freely without any intervention on our part.
Last winter a botanist with extensive experience in South Africa was one of those who expressed surprise upon seeing them flourishing in our yard, and reported that Daubenya has the reputation at Kirstenbosch, the national botanical garden at Cape Town, of being nearly impossible to cultivate.
It was fortunate that seed was set, for one November, when the leaves on the mother plants had not appeared, we found they had rotted.
Now, to search out an explanation for these discrepancies in behavior.
Daubenya aurea is a narrow endemic found on the Roggeveld, an escarpment that rises to nearly 5000 feet on the eastern edge of the Great Karoo desert. The plantsman, Harry Hall, who rediscovered the genus 150 years after its initial introduction and subsequent loss, commented that he found them in full flower even though they had been covered with snow two weeks before.
Plants which are narrow endemics often face geographical barriers and have developed under a more restrictive set of environmental factors than plants with wider distribution.
The factors that may be isolated from the scanty habitat information are: cold and moist conditions through flowering time are suggested by the snow; the presence of snow in a country not noted for it also suggests higher elevations; that they flower with an impressive pair of well developed leaves so soon after snow indicates the cold is not sufficient to inhibit growth; the proximity to a desert and the presumed elevation suggests that they grow in an otherwise arid region with a long, dry, hot dormant period and wide diurnal fluctuations in temperatures for at least part of the year. It is probably not too amiss to consider that the Roggeveld resembles in many respects the Panamint Mountains on the western edge of Death Valley, but with a less extreme climate.
Daubenya has one of the shortest growing periods and is among the earliest flowering South Africans in our collection. The leaves appear simultaneously with the undeveloped raceme in early November; blooming commences in mid February and seed set is completed by mid to late May. The year of our bulbs' demise, their seedlings were under cover while the parent bulbs were not, and that year we had an abnormal and heavy rainfall at the beginning of September, followed by our usual early fall heat wave that allows no relief at night. Heat combined with humidity appears to be fatal for Daubenya. This along with their abbreviated growing period accord with the notion that they require a long dry dormancy.
Concord is some twenty miles distance from Oakland and one climate zone removed within the system of classification developed by Sunset Publication. This difference evidently represents the significant upper range for the cultivation of Daubenya. Concord's temperatures are roughly ten degrees higher than Oakland's during the day in summer and lower during the night in winter, while night time temperatures in summer and day time temperatures in winter are more comparable. This means that Concord has wider diurnal variation through most of the year, and with its many midwinter nights in the upper twenties is more accommodating of Daubenya. While Cape Town, whose average monthly temperatures are generally higher than those of San Diego, is in much closer proximity to the Roggeveld, it is much farther removed from it in disposition than either Concord or Oakland.
A vexing problem when obtaining bulbs from the southern hemisphere is that of acclimatizing them to a reversal of the seasons. Often they are shipped just before growth is beginning in the southern hemisphere and one must choose between allowing growth to commence and hope they will tolerate the higher or lower temperatures involved in this "off-season" period, or attempting to prolong their dormancy until the proper season arrives and hope they do not become too desiccated (as is more likely to happen in very young bulbs). Our experience has been with winter-growing bulbs and we have tried both methods with mixed and often unhappy results. Some general principles have been derived.
When imported bulbs are allowed to begin growth out of season, their growing period is usually short as they will go dormant as heat increases and, I believe, especially when night time temperatures remain elevated (and some will be prone to rot if their soil remains moist at this time. As a consequence, their following resting period is also abbreviated --- perhaps only two or three months --- before their winter finally arrives. Restarting them after so short a dormancy can result in poor growth or none at all. (One very fine Gethyllis was given up as a lost cause when it made no appearance at all the first winter, but has since thrived and multiplied.)
It appears one should consider the phasing-in period to be a full eighteen months for true bulbs rather than the six months one might expect.
Further we have found this an area where it is important to make the distinction between a morphologically true bulb and a corm, for a bulb is perennial and a mature corm is annual. This means that, once in growth, besides putting up leaves, stems, flowers and setting seed, a corm must replicate and possibly duplicate itself. For all this a long growing period is essential. If a corm has struck roots and begun to sprout, denying further development will most likely be the death of the plant. It seems best to pot corms and store them in a dry spot that is as cool as possible. (And hope they arrive in a completely dormant state.)
True bulbs are more likely to arrive with signs that growth has started. We have found that while bulbs can tolerate interruptions with relative impunity, they do seem to appreciate a short period of growth in which they can establish roots in their new soil, particularly if the root stock they arrive with is in poor condition. So we normally pot and water them in a shady arid protected area while the late spring temperatures remain benign... usually for six to eight weeks... before withholding water.
It is worthwhile to point out that, given an eighteen month phasing-in period, the delay associated with seed propagation is considerably shortened.
This is the point where I mount a soap box for a bout of proselytizing. If you desire uncommon bulbs, you will soon discover that for most your only recourse is seed and this may seem an insuperable drudgery. It did to us initially, but we learned patience with the practice and it soon became at least half the pleasure. Propagation by seed has a great many things to recommend it: it is far less expensive and you receive many more plants for your money; with more plants comes the possibility of interesting variants; if only a small percent of your seedlings survive, those that do are constitutionally disposed to live in your area and it is likely that prefabricated bulbs of the species would not be; you will gain a greater sensitivity to the dynamics of their growth; and with very little effort and without really knowing how, you too will soon be hailed as an expert. Finally, there is an intense satisfaction that comes with being a participant in conservation.
The process of handling seeds is the same as bulbs, with two exceptions: ours are given overhead protection during the first season and greater care is given to maintaining a moist condition at all times since seedlings are superficial. They are sown at the same time that bulbs from the same area are normally expected to become active. Since I'm not much given to needless labor such as transplanting and can't imagine it contributes much to a seedling struggling to produce a bulb along with leaves, the seeds are placed in the same soil and container in which they will flower some time hence. The soil is the same as I would use with a bulb and a dressing of fine pebbles is placed on top to conserve moisture and to aid in maintaining the seeds in place.
Do not discard seed after the first season if germination has not taken place. Give them the same resting conditions as bulbs and there is an excellent chance they will decide the time is right in a future year. Yes, patience is required. Seed of the Juno iris group has taken four years to germinate for us. Less you find that too depressing, let me recount the remarkable performance of one of the loveliest and most neglected of our native bulbs, Alophia drummondii. Seed of it was sown in the third week of February, germination took place in the second week of March and it yielded its first flower on July 5th.
It seems two subjects have been neglected that no self-respecting discussion of cultivation can afford to ignore. The first of these is fertilizing. I tend to neglect it as an activity as well. It is a practice that would no doubt enhance the performance of our plants. Such neglect, however, is only partially attributable to sloth.
It is salutary to consider that South Africa, which harbors the greatest numbers and diversity of the world's bulbous species, also contains some of the world's poorest soils for agriculture. This is not happenstance. A plant that has plenty of plenty has no need to develop such elaborate stratagems as bulbs. These underground storage containers are analogous to the happily named (for the purposes of this similie) root-cellars of our ancestors, a means to provide for lean seasons during abundance. But the prudent goodwife knew if she crammed more underground than would be actually needed, the result would be rot and ruin.
So I may only repeat what has been said many times before: be judicious and go easy on the nitrogen. Heavy fertilizing will enable you to bloat your plants to an extent that only a show judge could love, but it can also leave them susceptible to infection.
The last topic of cultivation to claim some attention is also the one I have found many folks most eager to get an inside track on, and a thoroughly dependable issue to revive lagging conversations among gardeners. It is the endlessly entertaining one of soil-mix. On a good night at horticultural meetings, the exchange it provokes suggests a gathering of Julia Childs, Fanny Farmer and Betty Crocker on PBS for The Ultimate Recipe Showdown and Shootout.
I don't mean to minimize the importance of the contents in potting soil, but rather to express distrust of the search for an Ultimate Recipe. I am myself in the process of altering the soil we use, and such is my confidence in the resiliency of the bulbs involved that I am certain they will survive this tribulation as well. While the components of potting soil may be easily set forth (and have been many times), the actual proportions will be determined by the materials and climate available in the particular areas they're used in. Special additions may be required by particular species, but of these no generalization is possible. The only sources for such information are the experiences of other gardeners with the species or ... you guessed it... habitat information.
With nothing new to add, I'll end with a recital of the general requirements and materials for a bulb medium. It must supply nutrients, including trace elements; any good top soil will provide this. Drainage must be good to avoid standing water; we add a heterogeneous grade of sand. At the same time it must be capable of retaining a constant supply of moisture to the roots; this involves the addition of organic material such as compost or peat moss; while for the avant garde gardener, a synthetic, high molecular weight, X-linked polyacrylamide, more popularly known as a Co-Polymer, is the answer.
Now then, any more questions?
These words were handed out to participants of the symposium, The Plantsmans' Garden, sponsored by the Friends of the University of California Botanical Garden, September 29, 1989, Berkeley, California. Stan Farwig gave a talk entitled: "Bulbs of the Southern Hemisphere" at that symposium.