Growing Perennials in Containers OH 69
Leonard P. Perry, Extension Professor
Container plantings have become popular in recent years for several reasons. There are many more decorative choices than ever before, in all materials and styles and shapes and sizes. Containers lend themselves to, and are an integral part of, another recent trend--exterior decorating of living spaces. Many live in condominiums, or have only small spaces for gardens, which containers lend themselves to readily. Containers can be purchased already planted, hence an instant landscape or gratification. Containers can also be changed out often during the season as plants come and go in bloom, particularly perennials, to create continuous bloom and a changing landscape.
In the past, annual flowers were the mainstays of containers. However with other recent trends towards more perennials, even tropical plants in the landscape during the growing season, almost any plant could be considered for containers. I have even used shrubs in containers for a year or two, purchased as small rooted plants and as they grow then transplanted from the containers into the landscape.
When annuals are used in containers, in all but the semi-tropical and warm climates, they often get frosted and die in fall, with containers emptied and stored for winter. If herbaceous perennials or even small shrubs are used, keep in mind that in containers their roots are much more exposed and susceptible to winter injury than if they were in the soil. So unless in warm climates, or very hardy plants, perennials usually must be brought indoors overwintered or else treated as annuals.
If overwintering indoors, most perennials must be keep quite cool, preferably around 50 degrees but even 40 degrees to freezing may be best for many. Many alpines need cool temperatures, yet may be killed near freezing. Many perennials hardy to warmers zones such as 7 to 9 (0 degrees F and above in winter) should be kept at 50 degrees or above, or may be injured. During winter, some perennials may continue to grow or bloom slowly, others may go dormant, and many may need the cool temperatures in order to bloom well the following year. Grown in warmer conditions, as in homes, they may get too tall and spindly from too little light at the warmer temperatures, and may not bloom the following year.
The containers and potting mix
Most anything that holds soil may be used for containers from the traditional clay pots, to the many types of plastics now available, to old recycled items like boots or watering cans with holes or crack, to antiques such as advertising canisters or old farm containers. Points to keep in mind with any are:
The three main concerns are watering, fertilizing and grooming. Plants in containers will need more watering than those in the garden or landscape, drying out more frequently. Depending on the size of the plant in relation to the container, size and type of container, soil mix, climate and growing season, watering may need to be done from every few days to once or twice a day. Keep this in mind when planning to be away for extended periods, even for a day or two.
If many containers in an area, they may be connected through small tubes to an automatic watering system. Mulches may also be used to conserve moisture. Plastic pots, or pots sunk in larger ones and surrounded with a material such as potting soil, compost or wood chips, will dry out slower and need less water.
Just as too little water can be a problem, so can too much. This can be caused by rainy periods, poor soil mix, poor drainage or just too much watering. If plants wilt, yet the soil is wet, this may be a sign of too much water and perhaps even root rots. Check roots to see if they are white, or have turned dark and mushy indicating a root rot. If the latter, remove diseased roots, repot the plant, and keep out of stresses until hopefully reestablished.
Water absorbing materials are added by some gardeners to container media to hold more water, thus meaning less watering. This could cause problems if a rainy season, pots staying too wet. Others don't find these materials, often resembling lumps of jelly, very attractive on soil surfaces.
Pots often need more fertility than similar plants in the soil, so feed according to directions on the myriad of products available. Many use slow release fertilizers in container soils, which may supply nutrients all season. Yet some of these are released with temperature, too much being released too soon in hot weather and too little in cool weather.
Keep plants groomed for shape, but its best to buy a perennial that will stay in the shape you want and tidy, thus saving this pruning. Prune off any dead or diseased or broken plant material, and flower heads or solitary flower stalks after bloom (unless an attractive seedhead).
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Lawrence Forcier, Director, UVM Extension System, Burlington, Vermont. University of Vermont Extension System and U.S. Department of Agriculture cooperating, offer education and employment to everyone, without regard to race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status.
Last reviewed 9/20/01