By John Jett, WVU Extension Service horticulture specialist
If you don’t have space for a vegetable garden or if your current site is too small, consider raising fresh, nutritious, homegrown vegetables in containers. A windowsill, patio, balcony, or doorstep can provide sufficient space for a productive container garden. Problems with soilborne diseases, nematodes, or poor soil can also be overcome by switching to container gardening.
Grow vegetables that take up little space, such as carrots, radishes, and lettuce. You may also try crops that bear fruits over time, such as tomatoes and peppers, for best use of space and containers. Dwarf or miniature varieties often mature and bear fruit early, but most do not produce as well as standard varieties. With increasing interest in container gardening, plant breeders and seed companies are working on vegetables specifically bred for container culture. These varieties are not necessarily miniature or dwarf and may produce as well as standard types if properly cared for.
Selecting a site
The amount of sunlight that your container garden spot receives may determine which crops you can grow. Generally, root crops and leaf crops can tolerate partial shade, but vegetables grown for their fruits generally need at least five hours of full, direct sunlight each day; they perform better with eight to ten hours. Available light can be increased somewhat by providing reflective materials such as aluminum foil, white-painted surfaces, and marble chips around plants.
Container gardening lends itself to attractive plantscaping. A dull patio area can be brightened by the addition of baskets of cascading tomatoes or a colorful herb mix. Planter boxes with trellises can be used to create a cool, shady place on an apartment balcony. Container gardening presents opportunities for many innovative ideas.
Many types of containers may be used for gardening. Clay, wood, plastic, and metal are some suitable materials. Containers for vegetable plants must:
- be big enough to support plants when they are fully grown
- hold soil without spilling
- have adequate drainage
- never have held products that would be toxic to plants or people.
Consider using barrels, flowerpots, cut-off milk and bleach jugs, recycled styrofoam coolers, window boxes, baskets lined with plastic (with drainage holes punched in them), even pieces of drainage pipe or cinder block. If you are building a planting box out of wood, you will find redwood and cedar to be the most rot-resistant. Keep in mind that cedar trees are much more plentiful than redwoods. Wood for use around plants should never be treated with creosote or pentachlorophenol (Penta) wood preservatives. These may be toxic to plants and harmful to people as well.
Some gardeners build vertical planters out of wood lattice lined with black plastic and then filled with a lightweight medium. They can also be made out of welded wire shaped into cylinders, lined with sphagnum moss, and then filled with soil mix. Depending on the size of your vertical planter, 2-inch-diameter perforated plastic pipes may be needed inside to aid watering.
Whatever type of container you use, be sure there are holes in the bottom for drainage so that plant roots do not stand in water. Most plants need containers at least 6 to 8 inches deep for adequate rooting.
As long as a container meets the basic requirements described above, it can be used. Using discarded items imaginatively or constructing attractive patio planters is a very enjoyable aspect of container gardening. For ease of care, dollies or platforms with wheels or casters can be used to move the containers from place to place. They are especially useful for apartment or balcony gardening so that plants can be moved to get maximum use of available space and sunlight and to avoid destruction from particularly nasty weather.
A fairly lightweight potting mix is needed for container vegetable gardening. Soil straight from the garden usually cannot be used in a container because it may be too heavy unless your garden has sandy loam or sandy soil. Clay soil consists of extremely small (microscopic) particles. In a container, the bad qualities of clay are exaggerated. It holds too much moisture when wet, resulting in too little air for the roots, and it pulls away from the sides of the pot when dry.
The container medium must be porous in order to support plants because roots require both air and water. Packaged potting soil available at local garden centers is relatively lightweight and may make a good container medium. Soilless mixes such as peat-lite mix are generally too light for container vegetable gardening, not offering enough support to plant roots. If the container is also lightweight, a strong wind can blow plants over, resulting in major damage. Also, soilless mixes are sterile and contain few nutrients, so even though major fertilizers are added, no trace elements are available for good plant growth. Add soil or compost if you wish to use a sterile mix.
For a large container garden, the expense of prepackaged or soilless mixes may be quite high. Try mixing your own with one part peat moss, one part garden loam, and one part clean coarse (builder’s) sand, and a slow-release fertilizer (14-14-14) according to container size. Lime may also be needed to bring the pH to around 6.5. In any case, a soil test is helpful in determining nutrient and pH needs, just as in a large garden.
Plant container crops at the same time you would if you were planting a regular garden. Fill a clean container to within 1/2 inch of the top with the slightly damp soil mixture. Peat moss in the mix will absorb water and blend much more readily if soaked with warm water before the mix is put into the container. Sow the seeds or set transplants according to instructions on the seed package. Put a label with the name, variety, and date of planting on or in each container.
After planting, gently soak the soil with water, being careful not to wash out or displace seeds. Thin seedlings to obtain proper spacing when the plants have two or three leaves. If cages, stakes, or other supports are needed, provide them when the plants are very small to avoid later root damage.
Pay particular attention to watering container plants. Because the volume of soil is relatively small, containers can dry out very quickly, especially on a concrete patio in full sun. Daily or even twice-daily watering may be necessary. Apply water until it runs out the drainage holes. On an upstairs balcony, this may mean neighbor problems, so make provisions for drainage. Large trays filled with coarse marble chips work nicely. However, the soil should never be soggy or have water standing on top of it. When the weather is cool, container plants may be subject to root rots if kept too wet.
Clay pots and other porous containers allow additional evaporation from the sides of the pots, and watering must be done more often. Small pots also tend to dry out more quickly than larger ones. If the soil appears to be getting excessively dry (plants wilting every day is one sign), group the containers together so that the foliage creates a canopy to help shade the soil and keep it cool. On a hot patio, you might consider putting containers on pallets or other structures that will allow air movement beneath the pots and prevent direct contact with the cement.
Check containers at least once a day and twice on hot, dry, or windy days. Feel the soil to determine whether it is damp. Mulching and windbreaks can help reduce water requirements for containers. If you are away a lot, consider an automatic trickle irrigation system.
If you use a soil mix with added fertilizer, your plants will have enough nutrients for eight to ten weeks. If plants are grown for a longer period, add a water-soluble fertilizer at the recommended rate. Repeat every two to three weeks. An occasional dose of fish emulsion or compost will add trace elements to the soil. Do not add more than the recommended rate of any fertilizer since this may cause fertilizer burn and kill the plants. Container plants do not have the buffer of large volumes of soil and humus to protect them from overfertilizing or overliming. Just because a little is good for the plants does not guarantee that a lot will be better.
Vegetables grown in containers can be attacked by various types of insects and diseases that are common to any vegetable garden. Plants should be periodically inspected for the presence of foliage-feeding and fruit-feeding insects as well as diseases. Protect plants from very high heat caused by light reflection from pavement. Move them to a cool spot or shade them during the hottest part of the day. Plants should be moved to a sheltered location during severe rain, hail, or wind storms and for protection from spring and fall frosts.