Hostas can be propagated only in two ways - by their seeds or by root division. This also takes tissue culture (also known as micro-propagation) into account. Among these two methods, normally division is most practical.
The easiest way to divide hostas is to take out a portion in the form of a wedge from the clump using a spade, somewhat in the form of a cake slice. Subsequently you plant this piece of the hostas clump somewhere else or pot it up. The space left owing to the removal of the slice can be refilled using some fertile soil or some garden compost, such as decomposed material. When this is done, the parent plant will grow again in the new soil or compost and after a few weeks, you will hardly be able to detect the spot from where you removed the slice. Alternatively, you may also excavate the entire hostas clump and divide it into two or even more parts with the help of two forks end-to-end. Irrespective of the method you adopt, the entire operation ought to be undertaken during the spring, just when the noses start appearing through the soil. You may also carry out the operation during autumn when the leaves are beginning to die down. If you wish to have more hostas young plants, it is advisable that you either excavate relative bigger blocks from the original clump, maybe three quarters and divide the part into two or say three big slices; or you may excavate the entire clump and subsequently shake off or rinse to get rid of the soil. When you have done this, you are able to clearly see the white-hued roots or rhizomes of hostas. At this stage it will be easier to slice them into smaller parts. Each new plant will have roughly three to five buds. A single terminal bud is the smallest part that you can sensibly divide hostas into. In other words, the smallest unit is the bud that appears at the end of every little length of a rhizome. Nevertheless, when you want a somewhat larger quantity, you may often influence the dormant buds to growth. Usually, these are petite mauve colored buds that grow on the rhizome just underneath the terminal buds. What you should do foremost is to ensure that latent buds are actually present on the shoots. Once you have found them, cut off the terminal bud using a very sharp knife and subsequently divide the rhizome lengthwise, something similar to slicing a carrot longitudinally. Ensure that every long, slender rhizome slice has a solitary latent bud and, preferably, also retains a number of the original plant's roots. Remove all dust from these small parts or plantlets using fungicidal powder before potting them in any uncontaminated potting medium. Ensure to stand out these plantlets in an open, but shaded position. In case you keep them in a closed environment, the possibilities of these plantlets being affected by fungi are much more. It is worth mentioning here that dividing the hosta rhizomes into such small pieces do have some amount of risk, as if these plantlets are infected by fungi, then all of them may possibly be lost altogether. You can prepare the hostas for the purpose of propagation by various methods, which facilitates them to make additional buds compared to what would have occurred in the normal way. In fact, this is the more prudent technique to produce copious divisions of hostas. The first thing to do is a practice called simply mowing. This involves cutting the leaves of hostas just around 0.5 cm to 1.0 cm (1/4 inch to 1/2 inch) higher than the ground level, subject to the vitality of the hostas variety. When you do this, it helps the buds to start growing, and, in this way, they produce additional growing tips. In fact, if you wish, you can mow the hostas twice in one season. There is another method of preparing hostas for propagation. This method is called the Ross method and the term has been named after Henry Ross, an American inventor. This method involves scraping away the earth from the region of the hosta's crown, exposing the rhizome. You can do this by inserting a razor-sharp knife into one side of the rhizome somewhat higher than the basal plate and pressed downwards all through the basal plate to the region of the plant's roots. Subsequently, you need to take out the knife and insert it into the same side of the stem. However, this time the knife should be inserted perpendicularly to the place where you made the first cut. Then remove the knife and get rid of the soil in the region of the hostas crown. Next, water the crown. During the next few weeks you will notice some leaves of the plant becoming yellowish, while some others may turn blotchy. However, soon the hosta plant will get back to its original healthy look. By the time it is autumn, the plant will be having several additional buds compared to what would occur normally. Some growers have found that this method is successful even when it is practiced later during the season. However, it is interesting to note that simply crushing the shoe's heels into the young hostas shoots just when they are about to emerge during the spring may possibly be equally effectual in generating additional buds, but with much less effort. Generally, the best time to propagate hostas is during the spring just as the young shoots start emerging. Nevertheless, this is not a hard and fast rule. It is possible to divide the hostas throughout the growing season, in case you have cut the leaves of the plant after the division is done. It is also subject to the fact that the plants are well established in the soil or the growing medium and you have watered the new plants properly. The growth of hostas is more rapid when they are grown in sunlit conditions. This is the main reason why many growers in nurseries prefer to grow the young plants in field rows. Nevertheless, when grown in sunny locations, some of the leaves are likely to be burnt. In addition, hostas can also be propagated by means of tissue culture or micro-propagation, which is just an extension of the usual division. This technique is practiced in the laboratory and this involves taking the cells from the flowering shoot tips and growing them in a test tube containing sterilized jelly. These cells can be developed into minute plantlets by influencing their feeding as well as lighting. These minute plantlets bear resemblance to the parent plant whose flower has been used for micro-propagation. The cells taken from the flowering tips of hostas can be divided many times, making it possible to generate copious plants very quickly in comparison to what is produced using the older techniques. In fact, using the micro-propagation or tissue culture technique has enabled botanists to produce several new hostas varieties very fast, especially in terms of employing the older methods. This has also made it possible to put a greater number of plants on the market at a very early stage, sometimes even prior to the varieties being tested properly in gardens or before undesirable varieties have been eliminated. There may be other reasons for dividing a hosta, for instance in case it is detected that a sport has emerged on an established hostas clump. In this case, usually the safest technique is to wait till the sport re-emerges all over again consecutively for two or three years. If it does, uproot the portion of the plant that has emerged along with a few of parts of the clump neighbouring plants that have not been sported, if possible employing the slice of the cake method discussed earlier. Subsequently, you can place the entire slice on any potting bench with a view to bring it closer to the level of the eyes. You need to shake off and rinse all the earth attached to the part. This will make it easier to identify the precise portion or portions of the root to which the sport belongs. The remaining part of the root may be cut using a sharp knife. Pot the sport and continue to grow it. However, the sport may take several seasons to establish itself, as it will have a propensity to transpose to the parent plant.
Several varieties of hostas bear large quantities of seeds and nearly all of these seeds will germinate without any problem, thereby producing plenty of seedlings. However, if one allows the seed heads to remain on the plants for their ornamental effects during the winter and provided they are scattered all over the garden, the seedling will generally grow as weeds, until the gardener initiates appropriate measures to prevent the weeds from invading all over the place. In order to avoid this menace, it is best to get rid of the hostas scapes after the formation of the pods. However, the hybrid miniatures generally produce lesser flowers and do not seed very easily. It is unlikely that hostas that are naturally propagated from the seeds in a garden are not of any especial value. Firstly, hostas raised from seeds usually do not develop in true form. In other words, usually the seedlings will not have any close similarity or likeness to the parent plants. This is, however, not true for one species - H. ventricosa, which is apomictic by nature. In addition, hybridizers who are practicing premeditated breeding schemes have raised our anticipations to such an extent regarding what a high-quality hosta plant ought to be like, that very few seedlings will live up to these expectations.