Growing Vegetables in Containers

If you do not have space for a traditional vegetable garden, consider raising fresh, nutritious, homegrown vegetables in containers. A window-box, patio, balcony or even just a doorstep can provide sufficient space for a productive container veggie garden.

Grow vegetables that take up little space – such as carrots, radishes, and lettuce or crops that yield over a period of time, such as tomatoes and capsicums. The amount of sunlight that your container garden receives may determine which crops can be grown. Generally, root crops and leaf crops can tolerate partial shade. Vegetables grown for their fruits generally need at least 5 hours of full, direct sunlight each day, but perform better with 8 to 10 hours. Available light can be increased somewhat by providing reflective materials around the plants, such as aluminum foil, white-painted surfaces or marble chips.

Containers: There are many possible containers for gardening. Clay, wood, plastic and metal are some of the suitable materials. Containers for vegetable plants must:

1. be big enough to support plants when they are fully grown,

2. hold soil without spilling,

3. have adequate drainage, and

4. never have held products that would be toxic to plants or people.

Consider using barrels, flower pots, window boxes, or baskets lined with plastic (with drainage holes punched in it). If you are building a planting box out of wood, you can use rot-resistant hardwood or treated pine – provided that its thick enough to take the weight.

Whatever type of container you use, be sure that there are holes in the bottom for drainage so that plant roots do not stand in water. Most plants need containers at least 15-20cms deep for adequate root development.

Potting Mixes:
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 undesirable qualities of clay are worse. 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.

Container medium needs to be porous because roots require both air and water. Packaged potting soil available at local garden centres is relatively lightweight and may make a good container medium. Soil-less mixes such as a peat-lite mix are generally too light for container vegetable gardening, since they usually will not support plant roots sufficiently. If the container is also lightweight, a strong wind can blow plants over, resulting in major damage. Also, soil-less mixes are sterile and contain few nutrients, so even though major fertilizers are added, no trace elements are available for good plant growth. Add potting soil if you wish to use a peat-based mix.

Planting:
Plant container crops at the same time you would if you were planting a regular garden. Fill a clean container to within a few centimetres of the top with the slightly dampened soil mixture. 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 out 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.

Watering:
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 create problems with the neighbours, so make provisions for water 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 maintained 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 or not it is damp. Mulching and windbreaks can help reduce water requirements for containers.

Fertilising:
If you use a soil mix with fertilizer added, then your plants will have enough nutrients for eight to 10 weeks. If plants are grown longer than this, add a water-soluble fertilizer such as Thrive or Nitrosol at the recommended rate. Repeat every two to three weeks. An occasional dose of fish emulsion, compost or a Seaweed extract like Seasol 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. Just because a little is good for the plant does not guarantee that a lot will be better.