By John Pohly, Colorado State University Cooperative Extension agent, horticulture
Container gardening is the city dweller's answer to the big backyard garden of yesteryear. You may not have a half acre to plant in flowers and vegetables, but you can get just about the same effect by growing plants in pots.
Containers come in a variety of sizes, shapes and materials. What you choose will depend upon the type of plant and the location. A bonsai, for example, usually will be grown in a small container that won't allow a large expanse of roots to develop. A regular tree in a planter along the street will need a large container to allow for development of a larger root system.
You also can use planter boxes of varying sizes to grow vegetables and flowers on balconies and patios. Or fill an old discarded wheelbarrow with soil, poke drain holes in the bottom and use to grow geraniums and cascading petunias.
As you think about the size of the container, consider that when filled with moist soil, weight can be a major factor. If you are planning on a large container, mount it on casters so it can be moved easily.
Beware of decorative planters that lack drainage holes. This creates water-logged soil and rotting roots. Research shows that the old practice of placing a layer of gravel in the bottom of the container, to give some room for water to accumulate without saturating the soil, doesn't really work. If you want to use a decorative planter that doesn't have a drain hole, put your plants in a regular flower pot and place it inside the decorative container.
If you build a planter from wood, use a wood that won't rot. Or, line the planter with a water-resistant material. You can use CCA-treated wood or a natural rot-resistant wood, such as redwood. Don't use any wood that has been treated with Penta or Creosote. These materials are toxic to plants. Penta and Creosote no longer are available to the public, but some wood treated with these materials is still around.
Soil to be used in containers should contain plenty of organic matter. A heavy clay soil will hold too much water and will exclude oxygen that roots need for growth. A good brand of potting soil should work well.
Fill the container about four-fifths full of the soil mix. When you water the mix, it will settle and you will have enough room between the top of the container and the top of the soil for adequate water to be poured in each time you water the plants.
Because the volume of soil in the container usually is not great, you may need to water every few days. Factors influencing the time between waterings include size of plant within the container, volume of soil to store the water, porosity of the soil mix and porosity of the container. A large plant in a small container will require watering every few days, or maybe every day in sunny, hot, windy weather. Porous containers, such as unglazed clay pots, will let the soil dry out much faster than a container with a sealed outer surface. A sandy soil mix will not hold as much water as a heavier clay type of mix.
The possibilities for container gardening are endless. Apartment dwellers can grow vegetables in containers on balconies. Varieties have been developed specifically for container use. Yellow Canary tomato is a compact 6-inch plant that is designed for growing in pots. Red Robin and Goldie tomatoes work well in hanging baskets. Watermelon plants that grow 3 to 5 feet across, can produce 12 to 14-pound watermelons.
A lot of us like to grow tropical plants, such as citrus trees or dwarf bananas, in containers. Because of our short growing season, these can be planted in large containers that can be rolled around. If you have a large south-facing window, place them in front of that window in the winter when the sun is low in the south. Then move them outdoors in the summer. You will not corner the market on citrus fruit production, but a lot of people get a fair amount of production growing this way.
Container gardening is limited only by the imagination. It can be the simple potted plant on a windowsill or an elaborate balcony garden.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010