The best way to make soil humus rich is to dig in lots of compost and well-rotted manure. Rich humus soil is black. It holds water, yet is well draining. It is loose and friable, allowing plant roots to grow unrestricted. Soil rich with humus contains many organic nutrients that break down slowly into a form that plants can use. Nutrients from compost and manure build up in the soil, reducing the need for artificial fertilizers.
Things You'll Need
Make your own compost or buy it. Compost is available in bags from nurseries. Many landfill sites make compost from organic yard wastes. It is available by the truckload or large container, for a nominal fee.
Buy well-rotted manure, which is available in bags from a nursery, or you can get it from a local farmer or horse owner. There is usually no fee since they are glad you are taking it away. Get the manure from the oldest pile in the barnyard. Old manure contains no weed seeds and it will not burn plant roots.
Dig compost and manure into the garden before planting. Apply it as a side dressing around the crowns of plants to increase nutrition. Use compost and manure as a mulch to keep down weeds and retain soil moisture. Use as much compost or well-rotted manure as you need to make the soil friable. You can never use too much.