Without seeing the problem and knowing precisely what has been done to the plants, we cannot determine the cause of the problem. Several points you may want to consider:

Soil- It should be well drained and clean for container grown crops, not just soil dug from the garden. Most commercial soil mixes you purchase are satisfactory. For crops growing in beds, the addition of organic matter such as peat moss, compost, etc. will improve drainage and aeration, which is important to most crops.

Water- Watering is often considered an art, not a science. It is likely the single biggest cause plants do not perform to their maximum potential for the home gardener. Do not dry to the point of wilting or over water. The growing container or basket should have drainage holes. When watering, always apply enough water to have some drip from the container. Re-water when the soil an inch or so deep in the container seems moderately dry to the touch.

Fertilizer- Too much can cause burn. Use at the recommended rate or less at regular intervals. In general, the more often you water a plant the more often fertilizer needs to be applied. When applying liquid fertilizers to a crop it is advisable that the soil not be too dry. A slow release type fertilizer, such as Osmocote, may be a good choice for plants that must be watered often or liquid fertilizer is too inconvenient to apply.

Temperature and Light- Each crop has specific requirements. If the requirements are not met, the crop's performance will suffer.

Pests and Diseases- Thoroughly check the plant for insect and disease damage. Aphids, worms, mites, and thrip are common plant pests. Mites and thrip are often so small they are hard to see. Diseases, such as root and stem rots and foliar blights, are also common. If using pesticide to control these problems, follow the directions carefully.

We hope this helps you to determine the possible cause of the problem you are experiencing with your plants.