Growing vegetables in fiberglass pots is an alternative to growing vegetables in the ground and has some advantages. When vegetables are planted in fiberglass pots, they are protected from soil-borne diseases and can be protected if freezing weather threatens. Fiberglass pots are long lasting, do not break easily, and are lightweight. Depending on the size of the container, nearly every vegetable that can be grown in the ground can be grown in a fiberglass pot. Some popular choices of vegetables for planting in fiberglass pots are tomatoes, squash, peppers and onions.
Select a fiberglass pot that is the right size for the vegetable you are going to grow. Because of space limitations, it is best to grow bush types of plants, such as bush beans or patio tomatoes, rather than long vining types of the same vegetables. For example, a one-gallon container can hold one cabbage plant or several lettuce plants. A five-gallon container can hold up to three tomato plants or a dozen onion sets.
Turn over the fiberglass pot and be sure there is a drainage hole in the bottom. If there is not, use an electric drill to drill one 1/2-inch drainage hole for every gallon size of the pot. For example a two-gallon pot needs two holes, and a five gallon pot needs five holes placed randomly around the bottom of the container. If the container is going to be placed flat on the ground and cannot drain properly from the bottom, place a drainage hole on the side of the container near the bottom to ensure drainage.
Turn the container right side up and place coffee filters over the holes and fill the pot with fresh potting soil up to 1/2 inch from the top edge of the pot. The coffee filters allow water to drain while keeping the potting soil in the container.
Plant your seed or plants at the correct depth according to the instructions on the seed package or plant label. Add water around the plants or seeds so they can settle. Add a 1/2-inch layer of decorative mulch over the bare potting soil and around the plants. If planting seeds, wait until the seeds sprout before adding mulch. Keep the seeds and plants moist so they can get established.
Place the container in full sun or an area where the sun shines on it at least six hours each day. In warm climates, such as the southern U.S., the container may need shade from the hottest afternoon sun. Morning sun is always best for container plants. Water when the top 1 inch of soil is dry. A fiberglass container does not dry out as fast as a clay pot, but can dry out faster than average garden soil.