This reduces root disturbance and allows seedlings to grow without competing with each other. Fertilizing Some soilless mixes used for container gardening do not contain fertilizers. In this case, you will need to add trace elements that plants would otherwise obtain naturally from garden soil. Slow-release fertilizers that supply all the nutrients needed for a container garden are available. Another reason to use a slow-release fertilizer is that nitrogen is slowly released to plant roots, providing the necessary fertility throughout the growing season without burning plant roots.
Fertilizers are salt and when overused can burn or kill plants.
Fertilizer salts can build up over time in soil mixes and porous container materials such as terra cotta. Wash porous pots with a 10 percent bleach solution before planting to remove salt buildup. Follow label directions on all fertilizers, and keep records of planting and fertilization dates. Watering The most critical and time-consuming part of maintaining container gardens is watering. This is particularly true as plants mature and roots leave very little soil in containers.