Plants by their very nature want to multiply and get larger, create seeds and spread. Lilies are masters at creating copies of themselves or creating new variations. Few types of plants have such a variety of ways to multiply, be it by clones or by seeds. All parts of the Lily seem to be able to create some from of bulblet or seed. The bulb creates bulblets, the stem can produce stem bulblets underground, some species and cultivars produce stem bulbils and of course the flowers produce seeds. Now humans have gotten their hand in multiplying clones of a prize new lily or commercial grown favorite, by tissue culture. With this method millions of clones can be produced using a small number of cells in a laboratory. In the lab by using tissue culture a prize clone can produce as many as 2 million bulblets in a two year time frame.
I will start with vegetative methods that lilies use naturally to reproduce themselves and some methods that bulblets can be induced to grow. Then I will talk about hybridizing and sexual reproduction in lilies.
The most basic form of asexual or vegetative reproduction of lilies is bulb division. As a bulbs matures it grows larger, when it reaches a certain size based on its internal genetics it will simply divide into two parts. The divisions are called offsets. Each offset will have a growing tip to grow a separate complete lily. When you see two stems growing real close together it is a good indication that the bulb has split. They stay attached to one another as long as they are not dug up and physically separated from each other. In time these two halves will increase in size and split again. The lilies will do this over and over again as long as they are not disturbed. Eventually however the clump will have to be dug up and separated or they will be over crowded and start to decline in vigor. The offsets can be separated by using a sharp knife or prying them gently apart by hand.
Some of the rhizomatous American hybrids will definitely need a knife to separate them. Rhizomatous bulbs need to be lifted with extreme care as they travel underground for a ways and produce offsets at points along the rhizome. When dividing these offsets make sure each segment has at least one growing point with clusters of white or cream colored scales. The scales are very brittle
Different varieties of lilies divide at different rates. Asiatics increase rapidly, Orientals are slower to divide. The LA hybrids seem to be the superstars as well as some Trumpet varieties. A lot of species lilies also increase rapidly, others take forever and are best left alone to divide at their own pace. Martagon lilies and their hybrids are one of those species that should not be disturbed if they are growing well.
Stem bulblets are juvenile bulbs that are produced between the top of the bulb and to top of the soil level. The number and size they grow is dependent on the species or variety, health and vigor of lily. Some grow large numbers in a single year. The size can vary as well from tiny barely noticeable bulblets to ones that are almost as large as the original bulb. Each bulblet will be complete with its own scales, growing point and roots.
The number and size of the stem bulblets is a direct result from the amount and health of the stem roots. LA hybrids can be very prolific in producing stem bulblets and they can grow up to the size of golf balls in a single season. Most Asiatics only get them up to the size of a marble. To increase the potential numbers of bulblets one needs to encourage good root growth. Light airy soils rich in humus are the best way to encourage the lily to produce the bulblets. Planting the bulb a minimum of 4-6 inches will ensure lots of stem underground for roots to develop.
Six to eight weeks after flowering is very important time for the stem bulblets to grow and fatten up. When the main bulb is lifted the bulblets can be removed from the stem, it is important to plant the main bulbs and the bulblets as soon as possible. You can plant them close to the newly replanted main bulbs and given room to grow should flower in a year or two depending on the initial size. Obviously larger ones will flower sooner than smaller ones. If you prefer to plant them in a nursery until they get to flowering size, be sure to label them carefully. If you want to greatly increase your numbers of bulbs rapidly you can remove the flower head before it has developed. This will put all the energy that would have gone to the flowers back into the plant and more numerous and larger bulblets will be developed.
A few species and their cultivars are well known for producing stem bulbils. The Tiger Lilies, L.tigrinum (lancifolium) are well know for their stem or leaf axis bulbils. Bulbils are usually a dark purplish-brown color may measure about 0.5 inches (1-2 cm). This can vary from variety to variety and stage of development. Some plants have more mature ones at the top others start developing them from the bottom so they are more mature. I leave my bulbils on as long as possible to get as big as they can, some even start to leaf out and grow roots on the stem. Mature bulbils will eventually fall off the stem by themselves to the ground. Once they touch the ground they will start to grow roots and pull themselves into the soil. Depending on how long your growing season is they can also put out a single leaf and start to increase in size. If your cold weather comes on early they will just get themselves ready to over-winter and be ready for the next spring.
Collected bulbils can be planted in rows like vegetable seeds in the late summer to get a starting growth before winter sets in. I collect mine and place them in labeled ziplock bags. Then I put them into the fridge for about a month to give them a cooling period. Once I take them out of the fridge I put them up into trays and place them under Florescent fixtures in my basement. These I will grow over the winter time and by spring the bulbils have gotten to be a good size. Then in the spring I bring the trays outside to harden off before planting them in the garden. They will usually start blooming the season after that. Just to show you how quickly you can increase a stock of lilies with bulbils I have one really nice dark red lily that I got way back into my lily collection. It was labeled Monte Negro. While it looks a lot like Monte Negro I do not think the actual Monte Negro produced bulbils. None the less from the one bulb I literally have a couple of hundred plants in various stages if growth. Even the ones that are in their first real stem stage produce bulbils. This one is literally taking over my garden, no that I really mind considering what it looks like.
The formation of bulbils can be induced in some varieties by cutting off the flower head before they get to the small bud stage. If a lily has flowered you can pull out the stem, lay it out on its side and cover it with mixture of peat and sand. In a few months you should have a number of bulbs to pot up. But remember the parent bulb has had its stem pulled out so it will not have the leaves to manufacture food for the next season. You may lose the parent bulb but you will have numerous identical copies from the stem bulbils to make up for the loss.
The lily bulb is composed of numerous scales that are attached to the basal plate. By removing some of the outer scales of large healthy disease free bulbs you can increase you lilies quickly. Using bulbils to propagate lilies was at one time the most favorite method, but because not all lilies naturally produce bulbils scaling has taken over as the most widely used method. Any lily can be scaled to make new bulblets. There are a number of ways to do scaling, but the first thing to do is make sure your plants your taking scales from are virus free. Unlike seeds the virus is in all the cells of the bulb and will be passed on the the new bulblets. Scaling is a good way to increase the stock of a slow dividing favorite or an expensive new cultivar that you only purchase one for your garden.
Scales can be taken at any time of the year, but the best time is mid to late summer after flowering has finished. Once the flowers are done the bulb can be lifted and the outer ring of scales taken off. The removal will weaken the bulb for the next season but it will recover. Another way to get scales if you do not wish to dig the entire bulb out is to dig down beside the bulb and just take off the scales.
When I do scaling I take the scales and place them into a ziplock bag containing damp Vermiculite. Then upon closing the bag I let them sit in the light until small bulblets are formed. This only takes about 2 weeks for me to see some tiny bulbs growing from the bottom of the scale where it attached to the Basal Plate. The bulblets will grow roots as well. Once they get to a decent size I open the bag to reduce the humidity, this will acclimatize the bulblets to the lower humidity levels when potted up in their trays. After a while they will put up shoots and grow on like regular bulblets. Quite often more than one bulblet will form on each scale. If you wish you can cut each scale horizontally in the middle and bulblets will form on the top part as well as where the scale was attached to the Basal Plate. If you want to make sure your scales do not get fungus you can soak them in a systemic fungicide for 15 minutes before placing them in the plastic bag.
Another method to do scaling is to push the scale into a tray of peat and grit or humus so that only a third is showing above the mixture. Water the tray and let it drain, then place it into a a transparent bag or clear tray lid if you have them. Keep the scales at around 18C (65F) but not above 21C (70F). In a couple of weeks you should start to see some tiny bulblets developing. When they get large enough they should be potted up individually. It is a good idea to put the bulblets into a cold storage for a number of weeks depending on the division. This will break dormancy and cause leaves to sprout. Asiatics need about a minimum of 6 weeks while Oriental species and hybrids need 12-14 weeks.
After they have been growing indoors either under lights or in a heated greenhouse for the winter, they can be planted out in the garden when the soil temperatures are favorable. They may take a season or more to get to blooming size depending on how well they are growing.
Scaling is a good way to increase the number of a newly purchased quickly. This not only gets you more for your money but also acts like an insurance incase something unexpected happens to your bulb, such as squirrels digging them up and feeding on them.
Tissue culture is usually carried out in a laboratory and is used to make large quantities of a variety in a very short time. This method is favored by commercial growers as opposed to the local gardener. The cost is higher than scaling so only the newest most unusual clones are chosen.
To do Tissue Culture, small amounts of plant material is placed in a sterile nutrient medium, growth hormones are added to the medium to induce rapid cell division and differentiation. In time tiny bulblets are formed in huge quantities. It is possible to produce millions of bulblets in a few years. It will take another two years or so for the bulblets to be of marketable size.
Tissue Culture has been promoted as a way to produce virus free plant material. However, there is a process the material must go through to ensure no viruses are present. At the point where the tissue is initiated into culture it is tested with an ELISA (enzyme-linked immunosorbent assay) test for detection of common lily viruses. If a virus is detected it can be eliminated by Meristemming. This is a process in which very tiny pieces of rapidly growing meristem cells are removed, cultured and retested. This process repeats until virus free tissue is found. The rest is eliminated from further culturing. To get totally virus free tissue can take many repeats of the process and many months in time and money. This will raise the over all cost per bulblet to develop, which eventually means higher wholesale and retail prices per bulb. These new bulblets are not immune to viruses and can be re-infected when they leave the laboratory. So creating virus-tolerant varieties is still the ultimate goal of hybridizers.
Tissue Culture has been used on endangered wild species by using unopened flower buds. This is a good way to help bring back these species, but there is a draw back to this process. Since all the bulbs created by Tissue Culture are clones and exact copies of the parent plant, in time with declining numbers of wild specimens the majority will end up as the clone. This will ultimately have an effect on the genetic diversity of the plant. Propagating by seeds even in species there will be slight differences in the plants DNA (De-oxyribonucleic Acid) from specimen to specimen. These differences are what give a range of color, or growing height or vigor to a group of lilies in a given area. The diversity allows a group to over come changing climatic condition or a suddenly introduced viral or fungi infection. Some may survive these problems and be stronger thus creating a group of specimens that are better and healthier overall. In clones the DNA is all identical, so if the parent plant was very susceptible to a virus then the clones will be as well. This does not help the strengthen the species in any way, it just makes the numbers of individuals go up. If a virus hits a group of clones chances are they will all eventually die.
The actual process for tissue culture is complicated. But it is not beyond the limits of home gardeners who are willing to spend some time and money to multiply lilies.
The material for Tissue Culture normally comes from the bulb scales, however stem segments with an internode or flower buds can be used as well. The material should be virus free.
The first step is to sterilize the plant material in a 10 percent solution of household bleach and water for 20-30 minutes.. Remove and rinse, then cut into segments of approximately 5mm square in size. These are called Explants. The portion of the scale closest to the Basal Plate that produces bulblets is used. The explant is then placed in their culture vessels, usually test tubes with their growing medium. They are then wrapped in plastic and stored at 70F (21C). This is where allot of cultures fail due to contamination from soil organisms. If they due not become contaminated will produce bulblets in a few weeks.
If you wish to learn about Tissue Culture the internet or Lilium specific reference books are available. An excellent book on the subject is, Plants from Test Tubes (Kyte and Kleyn 1996)
Growing Lilies from Seeds