(Editor's Note: This article was originaly published on March 6, 2007. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
A little time spent in soil preparation will be well rewarded. If annuals have grown well in the bed before without fertilizer, then no additional fertilizer will be required for perennials beyond an annual maintenance light feed each year. If fertilizer is added to the bed, it is best done well in advance of planting or at least very well mixed into the soil. A light application of fertilizer to the top of the soil around the plants several weeks after planting or when the plants have begun to grow is always safe. All plant growing is a matter of judging plant response and deciding whether you are in the range of too much or too little, whether watering, spraying, fertilizing, as to temperature, sunshine, whatever. What you will be trying to achieve is a border that is established and can basically get along without any great effort each year. This is really a very realistic goal, and we hope that these plants and instructions will give you a good start in that direction
We suggest that you water the plants well in their pots the day before planting, especially if they have been held for any period of time after arrival. Extract the plants from their containers either by inverting the plant and tapping the pot's edge using a downward motion on a solid object, or by spanking the bottom of the pot to dislodge the plant. For 6 paks, a gentle pinch of the sidewall of the cell followed by a poke on the underside will free most plants. If it is still caught please tear open the cell pack to dislodge the plant. Then place each one in the spot it is to be planted. When that section is placed, plant each one a little below the soil line, firm it gently and leave a ring of ridged soil to hold water, if desired. When the whole bed has been planted, set a sprinkler or water by hand for at least 30 to 40 minutes. If there are rains at all, no further water should be needed until the first warmer dry spell.
Water and Summer Care
The first year, water will be required during prolonged dry spells. One inch a week is the general norm that is required. You can set a few cans in the border when watering to check the amount applied, or dig down a few inches a half hour after watering to see how deep the water has penetrated. A good six inches is ideal. Some new gardeners are very surprised to find that what they considered a good soaking is only wetting the soil to a depth of an inch or so. If plants are watered in that way they can turn out quite well, but they will be very shallow rooted and then hurt if a few days are skipped and the soil becomes dry at the top. You probably know of a good gardener who does not soak once a week, but lightly sprinkles every day. The secret of success is usually that they are very dedicated gardeners who do not leave town for any time during the growing season and just never miss a day sprinkling, unless it is raining. It is far better for almost everyone to strengthen their plants by deep watering when needed, and thus making their borders self-sufficient, which is more what perennial gardeners have in mind.
To keep weeds down, a light scratching of the soil as a few weeds are starting to show will destroy those as well as a multitude that are just starting to break out of their seeds. In order to germinate, seeds must be in the top of the soil layer, be in good contact with the soil, have ample moisture, and almost all have to be in the light. That is why once your new plants are up to size, the weed problem becomes minimal. As the plants mature and shade most of the ground and most weed seeds in the topmost layer have germinated and been destroyed by scratching or pulling, then scratching the ground can be more vigorous and watering less frequent.
The plants are insect and disease free for the most part. You should need no spraying unless a major invasion of sucking or chewing insects moves in from somewhere nearby, in which case the damage is easily apparent in time to use a general insecticide such as SEVIN or a general purpose spray before any real damage is done.
Mulching - Decorative / Weed Suppression
Personal Choice. The Pro's: It will keep the root zone cooler, and helps retain soil moisture. Looks nice and helps control weeds. The Con's: Can be expensive, won't stop grassy weeds, will tie up Nitrogen as it decays, and can repel water if it totally dries out. We like to apply a shallow layer (1-2") about 6 weeks after planting. This will allow you to cultivate the soil several times thus killing all the weeds as they germinate. Take care not to cover the crown of the plants. You'll find that additional mulch next year may not be necessary as the plants will fill in nicely and help control weeds themselves.
Fall and Winter Care
It is usual to cut the entire bed down to about 6" in late fall to remove old debris that will be in the way next season. This is also a good time to pull out the dead annuals from the border so that there is no question in the spring whether a dead looking clump is really dead or a valuable perennial, not yet awake. Most perennials will show signs of life at the crown early in the spring, and with the annual tops gone the fall before, spring cleanup can be delayed quite a while, and no plants need to be lost to an overzealous worker.
A light application of fertilizer can be made anytime from late fall to early summer to maintain the health of the bed.
Mulching for Winter Protection
We do not recommend it except for extreme northern gardeners who don't have reliable snow cover. The plants are very hardy and should not require winter protection. Many, many more plants are lost to smothering and rotting than to temperature extremes. If you decide to mulch, remember to wait until the ground is frozen hard to apply it. Excelsior, salt hay, evergreen boughs, straw - anything that won't mat down and smother works well. (Leaves and grass clippings are bad.) The mulch will need to be removed with the first thaw. In Ohio we typically have December, January and February thaws, so we don't bother mulching as it would do more harm than good. If in doubt our advice is don't.
Moving and Increasing Plants
As you gain experience with perennials, you will want to change the position of some of the plants. All can be moved at almost anytime by lifting them with a good clump of soil intact around the roots. In early spring and in the fall the plants can be dug without soil on the roots, but when the plants are in growth, they cannot establish new hair roots in time to keep up with the demands of the tops. Plants can be dug and divided even after they have begun to grow in the spring, but the longer you wait, the more care they will need to reestablish themselves. If a plant is divided and reset and no wilting of the tops occurs, they are fine. If they do wilt they should be watered again or even shaded with a board or open box until new roots can start in two or three days. For a start, you might try cracking a piece off the side of some of your plants just after the ground warms, and transplant these to new spots, leaving the main part of the plant undisturbed. The Dianthus have a central stem and cannot be split, and the Astilbes have such a hard center that they would have to be dug in order to cut or divide them. Some of the plants, such as Coreopsis and Shasta Daisies will seed themselves and new plants can be saved once you learn to recognize the seedlings.