Marigolds help repel leaf eating pest in the garden. Grow on the edge.

Mint & Tansy will discourage ants. Tansy is also known to help keep borers away from fruit trees.

Chamomile with cabbages and onions will help keep cabbage moth away.

Dandelions and valerian will encourage earthworms.

Growing lavender, garlic, parsley, nasturtiums or chives will help protect against aphids.

Basil helps repel whiteflys. Should be planted around tomatos to keep flies and tomato worm away.

Make sure when you compost that you get a good mix of green material and brown material. Insufficient green waste means less nitrogen to activate micro organisms which do all the decomposing, and if brown wastes are not in sufficient quantity then nitrogen will be lost to the atmosphere and perhaps a sludgy smelly compost will result.