Getting Potted Plants Ready For Summer

05-01-2000
Potted plants are being used more and more as a part of both the indoor and outdoor landscape. Maintaining plants in containers -- no matter what size, shape or type -- presents certain problems.

Trees, shrubs, flowers and house plants all need sunlight or a good substitute source of light to do well. Water is also essential to move the nutrients from the soil into all parts of the plant. Water also distributes the plants food manufactured in the leaves during photosynthesis to various parts of the plant. If all the conditions necessary for growth are in balance, plants will flourish -- unless they are attacked by a pest or affected by mechanical or chemical injury.

I think most gardeners are aware of the fact that not all conditions are always favorable for growing potted plants. For success, you must first develop an understanding of the individual requirements of plants growing in the unnatural environment of a container. Most potted plants that do not grow well suffer from too much or too little water; an excess, lack or imbalance of soil nutrients; or an improper soil mix.

As soon as the weather warms a bit more, you should begin thinking about getting new plants, repotting old ones or simply moving some to the outdoor environment for the summer. A great number of problems can be controlled if you adopt the following practices this summer.

• When bringing new plants to your collection, check them carefully before purchase, then isolate them for at least two weeks and observe for insects, mites or disease. Any insects or mites can be controlled in their early stages of development with an insecticidal soap solution. Heavier infestations are better controlled with aerosol sprays.

• The right soil mix is important for potted plants. An ideal potted soil should drain well and be light textured. If you have very large containers with a volume of a bushel or more it may be possible to use a high-humus topsoil for growing plants. Commercial potting soil is a better choice for containers of smaller volume. Nearly all potting soil will be improved if you mix in 10 percent coarse material like sand or vermiculite.

• Unless you are using a commercial potting soil it may be desirable to pasteurize any potting material that contains garden soil. Moisten the mixture and heat it in an oven at a temperature of no higher than 180 degrees F for no longer than 30 minutes. Higher temperatures and longer time can damage the soil. Allow it to cool before using around roots.

• Once plants have been established in a container it is critical that they be kept uniformly moist. Even short periods of dryness can affect the quality of the root system and plant in general. Also under periods of moisture stress from dryness, the soluble salts in the soil tend to increase to toxic levels which causes further injury to the root system. Frequent overwatering can be as serious as underwatering.

• Fertilize the plants lightly and only when they are making active growth. During this period they will utilize the added nutrients. Don't use a high-nitrogen fertilizers when your plants are in bloom.

• Avoid soluble salt problems that may develop under a normal watering and fertilizer schedule by periodically flushing the soil with soft water where available. This leaching operation is accomplished by adding water equal to 4 to 5 times the soil volume in the container. This extra water pushes the mineral salts through the drain hole in the bottom of the pot. Discard the leachate that comes from the pot.

• Be aware of the light requirements of specific plants. Most flowering plants will need plenty of light while foliage plants that are moved from indoors can be damaged by full sunlight. Avoid sudden changes in light intensity or temperature because the shock can cause leaf or flower drop.

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**Dr. Robert Nuss is a horticulturist at Penn State. He coordinates all extension horticulture programs. He has bachelor’s, master’s, and doctoral degrees in ornamental horticulture and has been on the Penn State faculty since 1966.