Rick Durham, Consumer Horticulture Extension Specialist, University of Kentucky

Dormancy and plant maintenance.

So often we hear that fall or winter is a particularly good time to do certain things in the landscape. This is usually due to the fact that plants have entered into winter dormancy. Dormancy can be compared to an extended period of "rest" for plants when they are relatively inactive in terms of metabolic processes (photosynthesis, respiration, transpiration, for example). I say relatively inactive, because although these processes slow during dormancy they do not cease altogether. Most temperate perennial plants will enter dormancy in autumn as daylength shortens, as temperatures (including soil temperatures) become cooler, as terminal buds are set, and perhaps as a result of drier conditions during late summer and fall. Dormancy is the mechanism these plants use to survive the cold of winter. It is therefore important that our landscape maintenance activities not interfere with the plant's natural process of becoming dormant. Let's use pruning and fertilization practices as examples.

Fall is considered a poor time to prune most woody perennials. Why? Pruning will remove terminal buds that help to maintain dormancy in many species. The presence of the terminal bud, even in a seeming inactive state, suppresses the growth of lower buds through a process called apical dominance, a type of dormancy imposed on the lateral buds. If the apical bud is removed, this may encourage lateral buds to initiate growth if the plant has not yet fully entered a dormant state. Once lateral bud growth is initiated, dormancy will be hard to achieve, even with the advent of shortening daylength and cooler temperatures. So pruning in the fall may trigger new growth that delays dormancy and predispose the plant to winter injury. The recommendation then is to prune plants in late winter, around mid February to mid March. This will also allow for evaluation and removal of any damaged limbs as a result of winter injury. Also, pruning in late winter will occur just before one of the most active times of plant growth, bud break, when the plant is redirecting stored nutrients from the root system out to the branches. This would be the most rapid time for wound (in our case the pruned surface) healing by the plant while fall would be the slowest time for wound healing. So this is why we would generally recommend pruning in late spring as opposed to fall. Some exceptions. If the limbs being removed are dead or severely damaged due to breakage, insects or disease, it is best to remove them as soon as possible at any time of the year. If the plant being pruned is spring-blooming (generally flowering before early June), it would be better from a flowering display perspective to wait until after flowering to prune since the pruning process will remove preexisting flower buds.

What about fertilization of woody plants? Fall and winter are considered the best times to apply fertilizer, but this should only be done once woody plants are fully dormant. Otherwise, applying fertilizer might trigger new growth and predispose the plant to winter injury. How does one tell if a plant is dormant? If leaves are falling, the plant has probably entered dormancy sufficiently to allow fertilization. To be doubly safe, wait until temperatures are unlikely to climb into the 70F range. In Kentucky this could occur anytime from mid October to mid November, so to be absolutely safe this probably means mid November or later. Also, get the fertilizer down before the soil has frozen (say before Christmas) else the fertilizer will remain on the soil surface and will be subject to runoff with any additional precipitation. If you don't fertilize between Thanksgiving and Christmas, wait until the ground thaws in late February or early March to apply fertilizer. However you must realize that February and March are not the best times for applying fertilizer to lawns composed of cool season grasses (fescues, bluegrass, perennial ryegrass). If fertilizer is being regularly applied to the lawn, woody plants growing nearby are likely getting sufficient nutrients from these applications and would likely not need additional fertilizer.
 

Reuse straw from autumn displays.

Driving through my neighborhood a few days ago I noticed someone had placed a bale of straw next to the curb for pick-up by the city sanitation crew. My guess is they had just broken down their autumn display and had no use for the straw. However, straw makes a great mulch in the home landscape and now is the best time for its application. One word of caution. Straw contains seeds, both the seeds from the crop comprising the straw such as wheat, barley, or other grasses, and the seeds of any weeds that were growing with the crop. For straw that has become wet (as is often the case when used in an outdoor display) the seeds will usually germinate if they are close to the surface of the bale, or rot if they are located internally in the bale. If you plan to use fresh, dry straw for mulching, it is best to open the bale and moisten it thoroughly early in the fall which will promote germination of most of the weed and grass seeds. These young plants will be killed by the freezing temperatures that are soon to follow. Once there have been a few hard freezes, scatter the straw in perennial beds, use it as mulch in small fruit or perennial vegetable plantings, or mound it around roses to reduce drying and cold damage to canes. Applying the stray about 3 inches deep should be sufficient. Straw is much to valuable to the landscape to allow it to end up in a sanitary landfill.
 

It's not too late to plant bulbs.

You may have noticed that many retailers are putting their spring flowering bulbs on clearance to reduce inventory and make way for other displays. It's still not too late to get bulbs in the ground and enjoy some color next spring. Ideally we would like to have the bulbs in the ground by Thanksgiving, but they can still be planted as long as the soil is not frozen. Be sure to follow package directions regarding planting depth, and apply a layer of mulch over the soil surface to reducing freeze/thaw cycling. The biggest danger in planting bulbs this late is that the bulbs themselves may be of poor quality after staying on store shelves for so long. Select only firm, heavy bulbs and select against any that feel light, shriveled, or exhibit pockets of mold or rot. Adding a little bone meal to the planting hole will provide a source of slowly available nutrients to the growing bulb, however, the best time to fertilize will be in the spring once you notice new shoots arising from the soil. At that time apply a complete fertilizer, such as 10-10-10, at a rate of about 1-2 pounds per 100 square feet.
 

Move houseplants to a sunny window.

Many houseplants tend to suffer over the winter due to poor light, dry air, and too much water. Here are some tips to remedy these situations. Relocate houseplants to south facing windows to maximize their exposure to sunlight. If plants have been growing in extremely poor light, such as near a north facing window, move them gradually into the brighter light to avoid burning the foliage. Realize that plants near a window pane may suffer on cold nights since the glass may not be well insulated and foliage touching or very near the window may be exposed to freezing or near freezing temperatures. This would be less of a problem in windows with double-pane glass since the air space between panes serves as an excellent insulator. To increase the humidity around the plants, try placing them in pebble-filled trays where water can be maintained just below the bottom of the pots. Be sure that the base of the pot does not contact the water else the soil will not drain properly and remain too moist. The pebbled tray can serve as a drainage area to help ensure the plants are not over watered, and as the water evaporates it will increase the humidity near the plants. Realize that plants will require much less water during the winter than at other times of the year. Always check houseplants for moisture before watering by inserting a finger into the pot down to the first knuckle. If the soil feels moist, wait another day, and water only when the soil is dry to the touch.