Chapel Hill, North Carolina

As a nurseryman and grower of hostas, I watch what happens to the plants both above and below the soil, as opposed to gardeners who are mainly concerned with what happens above the soil.

In order to understand hosta physiology, it is important to know that a hosta is a monocot and what that means. Monocots have several characteristics that separate them from dicots.

First is the number of seed leaves. Monocots have one. Monocot is a shortening of mono, meaning one, and cotyledon, seed leaf. A newly germinated seed will only have one leaf, with one root. It takes some time for a second leaf to develop. [By a show of hands it was determined that most people in the room what until there are two or more leaves (and roots) before they transplant seedlings.]

The second difference is leaf venation. Monocot leaves have parallel veins versus the branching veins of dicots. It is harder for plants with parallel veins to pump enough water to stay cool in the heat of summer. Hostas in the wild are found in wet rather than dry areas. Branched veins are much better for transporting water. The more water that can be transported, the more efficient the plant is at cooling the leaf surface. Plants transpire water through the stomatas as a cooling system. Cooler leaves and cells are more conducive to other plant processes, such as photosynthesis.

Third is the root systems. Monocots have fibrous root systems while dicots have netted root systems. A hosta root grows from the tip. That is why there are only a few roots in the pot that seem to circle around and around. If they were stretched out, each one would be quite long. An individual root can live for 3-4 years. Breaking or damaging these roots during transplanting will stress the plant until it can grow more roots at the next flush of growth. Dicots with netted roots form new and branched roots when the roots are cut. Root pruning is a positive for dicots. Monocots with long, generally unbranched roots, are not as efficient as dicots in extracting water and nutrients in the soil. This is especially true if they are planted where they are in competition with dicots.

Monocots evolved earlier and are not as evolutionarily advanced. They are not as efficient as dicots when it comes to seed survivability, leaf and root form and function.

Next is a look at the life cycle of a hosta, starting from seed.

Each seed, being a monocot, has one wing on it. If it is germinated, the first thing to appear will be a small leaf. This will be followed shortly by a root. The hosta will continue to grow until it is a mature plant, when it can flower and reproduce. Assuming our seedling has grown into a mature plant, our discussion of the life cycle of a generalized hasta will begin in early spring, when the plant is dormant.

With the arrival of spring, the buds begin to swell and the hosta unfurls its first set of leaves in the spring. There are usually three leaves, as this is characteristic of the lily family, of which it is a member. The size of the leaf is dependent on what happened last fall, before it went dormant. More on this later. About three weeks after the leaves unfurl, the roots will begin to grow. New roots will be formed, and the tips of the old roots will turn white and begin to grow. Depending on the climate and what type of hosta, another flush of growth can occur again later in the spring. New leaves will be formed from this years growth, followed by new roots in a few weeks.

Sometime in the summer, the plant will switch gears and go from a vegetative phase to reproductive. Flower stalks will form and bloom. A show of hands was taken to show how many remove flower stalks as they appear. No one does, probably because it is so much trouble. Actually, it serves little purpose, as the flower was already formed the prior year. It is not the flower that takes strength from the plant; it is during seed production that the hosta expends a lot of energy and nutrients. In fact many people remove the flower stalk after flowering but before seed set.

After the hosta has bloomed and the heat of summer has moderated, our idealized hosta will send up another flush of growth. This usually occurs five to six weeks before the last frost date. After this final flush of growth, the hosta will again shift gears and get ready for dormancy.

Now we have examined the life cycle of our generalized hosta. But why is it important? Because it tells us when the best times are to divide and fertilize.

Fertilization: Obviously, the best time to fertilize is when the plant needs it. This would be in the spring, right before the first flush and again in the fall after flowering and before dormancy. A high nitrogen fertilizer in the spring is recommended. 20-10-10 applied per bag instructions is fine. Liquid fertilizers can be used, but keep in mind that the nutrients will only last a week, so it needs to be reapplied every week. To push a hosta to produce extra large leaves during the second flush, use a high nitrogen lawn fertilizer like Green Sweep (27-1-4). And just wet the leaves. For fall feeding, a balanced fertilizer such as 10-10-10 is good. Apply five to six weeks before the first frost date. These recommendations are for nitrogen and phosphorous. A soil test should be taken to see if other nutrients are needed.

Dividing: Keeping in mind our life cycle, the best time to divide would be in the spring between the first and second flushes of growth. Dividing before the first flush would damage too many roots. Remember, a damaged root will not regrow. By waiting until after the first flush, new roots will be forming, so the plant will not as stressed going into summer. The time for this is usually about 6 weeks before the first frost date, before the plant has begun to make dormant buds.

What happens when you transplant a hosta that is in a dormant state? When you dig it up, you risk breaking roots. New roots will not form until 3 weeks after the leaves have flushed. You could end up with a plant that is very stressed. But, there is a lot of energy stored in the crown of the plant, enough so that the plant will not die.

Remember those dormant buds that were formed back in the fall? The first flush of leaves appear from these buds. If the plant had been growing in the sun, it will send up large, water hungry sun leaves. Conversely, if it was in the shade it will send up smaller, delicate shade leaves. Moving the plant from sun to shade or vice versa, it takes some time for the plant to recognize the change and send up leaves appropriate to where it has been relocate.

I said that our life cycle was of an idealized hosta. Most hostas are not idealized, but rather fit into four broad categories. It is important to know the parentage of our plants. Hostas are native of China, Korea and Japan. With such a large geographic area, it is not surprising that there are many different species, each having quite different needs, depending on where it occurs naturally.

Based on how the plants grow, I have divided them into four groups which combine similar species. There are certain assumptions that can be generalized for each group.

H. sieboldiana Group: These types from cooler areas are accustomed to a short growing season. They emerge late in the spring and are in a hurry to flower, set seed and go dormant. They generally form one large dormant bud on the side of the crown. Usually there is only one flush of growth, occurring in the spring. Because they are used to cool temperatures, they can easily suffer from heat dormancy. Heat dormancy occurs when the plant shuts down because of temperatures above 95 F. The tissue actually will go to sleep, and remain that way all summer. The leaves will not die down, but can show signs for scorch. This is why sieboldianas are so prone to leaves burning and scorching. Because the plant is not growing, pathogens can gain a foothold and the crown will rot. Next spring, instead of a large eyes, you will get a series of rings of much smaller plants, due to the main bud dying and the smaller side buds growing. To combat the effect of heat dormancy, continue watering the plant. You want to keep the root tips growing. If the plant goes heat dormant, if you think that there is damage, you can dig the crowns up and dip them in a 10% Clorox solution to stop the spread of rot.

Remember the monocot versus dicot comparison? I have shown how dicots are much more efficient at getting water with their netted roots, and at cooling with their branched veining. Many hostas are planted under maples and other trees that are expert water gatherers. Competition is fierce and it is usually the monocot that loses. Over time, the soil gets compacted, making it more difficult to hold water. Maple roots have been known to actually encircle hosta roots, looking for water. You should dig out and cut back those invasive roots, and amend the soil to keep your hostas healthy. H. sieboldiana types do not have a flush of growth in the fall. Do not fertilize them. Fertilizing in the fall will be detrimental as it can burn already weakened roots.

H. nakiana Group: These are good growers. They have multiple flushes of growth in the spring, maybe two more after the first. They will flush again in the fall. They usually set three sets of buds per flush, so are good increasers, making good ground covers. Some examples of these are 'Blue Cadet', 'Lemon Lime' and 'Birchwood Parky's Gold'. Fertilize them 20-10-10 in the spring and 10-10-10- in the fall.

H. plantaginea Group (also sieboldii Group): These are tropical plants. They want to come up as soon as possible in spring and grow, grow, grow! They are easy to force and will grow indoors for a year or longer before needing a period of cold dormancy. They will continue to send up flushes of growth all spring and summer until flowering. Flowering time is late in the fall. Fertilize them all summer long, except when it is very hot. They need lots of water and will tolerate more light. Examples include 'Invincible', 'Fragrant Bouquet' and 'Guacamole'.

H. kikutii and tardiflora Group: These come up early and have one to two flushes of growth and bloom very late. They could be called the "plastic plants" of the hosta world, having tough, indestructible foliage. Their foliage will look good until frost. In hot weather, they can be semi-heat dormant, but the roots will continue to grow.

By keeping in mind the life cycle of the hosta, along with what group it belongs in, it is easy to know what is going on below the soil. Knowing what is happening at the root level, fertilizing and dividing is much easier. I hope that this information will help strengthen your monocot in its ongoing battle against the more numerous and formidable dicots of the world.

This article reprinted with permission from the American Hosta Society.

 Information on joining the American Hosta Society and its regional and local societies can be obtained from the AHS.

The American Hosta Society