All photos © to the author, B. Adams-Eichendorf.
In order to successfully grow lilies it helps to know what’s going on where it all starts...underground with the bulb. Lilies grow from bulbs which occur in a variety of shapes, colors and sizes.
The bottom part of a lily bulb is a solid basal plate which in botanical terms is actually a modified stem. This basal plate is the most important part of the bulb because it produces the roots, scales and buds for new growth. Firm, fleshy bulb scales grow upward from the basal plate. Botanically speaking, bulb scales are modified leaves which are used for nutrient storage. The bulb scales are loosely arranged in an overlapping pattern. When you look at the bulbs of different lily cultivars, you’ll notice that for some cultivars, the bulb scales are very tightly wrapped together, while other cultivars will show a much looser arrangement of bulb scales.
The scales of a lily bulb are not covered with a papery covering such as you would find on tulip bulbs or onions. Bulbs with the papery covering are called tunicate, and bulbs without the papery covering are called imbricate.
Lilies produce two types of roots: contractile and feeder. Contractile roots grow downwards from the basal plate and pull the bulb downward in the soil as it grows. This is a rather interesting phenomenon, as lily seeds germinate close to the surface of the soil, and over the course of a few years as the bulb grows larger, the contractile roots will have pulled the bulb down to a point where it is covered by a couple of inches or more of soil.
Contractile roots are thick and wrinkled looking, and are permanent roots. Feeder roots grow both from the basal plate of the bulb and in many lilies they also grow from the portion of the lily stem which grows underground above the bulb.
Not all lilies produce roots above the bulb but this is very typical of Asiatic lily hybrids and LA hybrids. The roots above the bulb are attached to the stem and are annual roots which die off at the end of the growing season.
Bulblets often form along the underground portion of the stem, in or near the area of roots above the bulb.
Bulb color varies with lily types. Martagon lilies are often yellow and egg shaped. Trumpet lilies and Oriental/Trumpet hybrids are usually purple. Asiatics and LA’s are usually white, though exposure to light will lend a pink tinge to their color.
Lily bulbs increase by dividing. Typically for Asiatic lilies and many others, once a bulb is mature, it will gradually divide into two bulbs, (sometimes more) then as these two new bulbs mature, they each will divide into two, and so on. The rate at which lily bulbs increase is dependent on several factors. First, each lily cultivar is unique and will increase at its own rate, with some increasing much faster than others. Secondly, bulbs grow and increase better if the plant’s cultural requirements are met: good drainage, plenty of light, adequate water and nutrients, and acceptable pH levels.
As well as bulb division, lilies have other methods of increasing. Many lily cultivars produce bulblets below soil level, and some cultivars and species produce small blackish bulbils in their leaf axils. The leaf axil is the point at which the leaf meets the stem.
At right: a clump of Martagon lily bulbs badly in need of being separated and replanted. Lily bulbs usually need to be lifted periodically and the bulbs separated and planted into fresh soil. Martagon lily bulbs are often slow to increase, so it takes many years for them to get as crowded as the ones at right. Depending on conditions, Asiatics and LA’s need to be separated more often, usually every three to six years, depending on the cultivar.
At left, the rhizomatous bulbs of Lilium canadense, which is a species lily native to eastern North America. With rhizomatous bulbs, the daughter bulbs form at the end of a very short branch which grows out from the mother bulb. This is quite unlike what happens with the concentric bulbs of Asiatic, Martagon and many other lilies, where the growing point is centered, and the mother bulb divides at this center point to form two or more daughter bulbs.
You’ll notice on these bulbs that the bulb scales are quite different in shape from the scales of bulbs shown in previous photos. I have had very little success trying to grow several of the North American species lilies which have rhizomatous bulbs. Those that I have tried, including L. michiganense, L. pardalinum and L. canadense managed to survive and bloom for a couple of years in my yard before disappearing. Though they seemed to be easily able to stand the extreme cold of our winters, I think that our typically dry soil conditions and the high pH of the soil (alkalinity) led to their demise.
Three characteristics mentioned earlier help us to determine storage requirements for lily bulbs: they are never completely dormant, the basal roots are permanent roots, and the bulbs are imbricate (without a papery covering). In order to keep the bulbs and roots from drying out, and from sprouting prematurely, bulbs are best stored in cold conditions, (ideally just above freezing) packed in slightly damp peat moss in plastic bags. Bulbs bought at Gardenscape can be stored in your fridge until you are ready to plant them.
Though removal of the basal roots and won’t actually harm the bulb, it will take energy for the bulb to produce a new set of basal roots. As bulbs have a finite amount of energy to use, they’ll probably produce less flowers while their energy is redirected to making roots.
by B. Adams-Eichendorf (CPLS Newsletter March 2017)