Without a doubt, the best soil amendment in the world is compost. But not everyone maintains a compost pile or bin.
So then what? There are a number of bagged products that represent the next-best thing to homemade compost.
Some good options are pure cow manure, topsoil and mushroom compost. Each of these can be used separately to amend the soil, but try mixing them to get the best that each has to offer.
If you are going to create a mix, consider adding a little helping of bone meal, high in phosphorous and calcium. It won't rapidly stimulate plant growth, but is essential for growth and stimulates microbial activity.
Once you've got your mix down, it's time to add it to the soil.
The simplest way involves tossing 2-8cm of the stuff on top of the existing soil and letting nature do the rest. In time, organic matter will break down with the help of earthworms and various small microbes.
You can also gently work the organic matter into the soil by turning the top 15cm or so.
If you intend to amend an already mulched bed, you'll first need to pull the mulch back and then apply the soil amendment, and, finally, put the mulch back.
If you don't want to go to all the trouble, or if you're short on soil amendments, simply apply the stuff around the perimeter of established plants. Think before you work it into the soil, though, because you could damage plant roots.
