Main amendments

Amendments are substances added to the soil to improve its physical, chemical and biological properties. They fall into two categories: organic amendments and mineral amendments.

Organic amendments

Compost

Compost is formed by the fermentation and wetting of animal manure, dead leaves, grass clippings, kitchen scraps (fruit and vegetable trimmings and egg shells), garden waste, etc. Compost makes an excellent amendment and fertilizer for the garden: it adds microorganisms to the soil, provides them with nutrients and shelter, improves the soil structure, balances the pH and supplies plants with essential nutrients. Because these nutrients are released gradually, the plants enjoy a steady food supply.

When to apply it

Early spring is the best time to add compost to sandy soil (so that fewer nutrients will leach out), and late fall for other soil types. Avoid adding compost during a heatwave or the hardening-off period.

The hardening-off period extends from late summer until the leaves fall. During this time, plants get ready for winter: growth is halted, tender twigs on trees and shrubs turn woody (lignified), buds form that will open in spring and the stores of nutrients made by the leaves accumulate in the roots and underground organs. Adding compost at this time may promote the growth of tender shoots that will not have time to harden off before winter.

How to apply compost

• When preparing a bed, work compost into the top 10 to 15 centimetres. To maintain planted beds, dig the compost in lightly or simply cover it with mulch.
• To promote proper root growth, compost should be applied to the entire planting area and not just around the plants.
• To ensure that your plants have access to a complete and varied source of nutrients, it is best to use different types of compost over the years (shrimp compost, sheep manure compost, leaf compost, backyard compost, etc.). All compost you use should be well decomposed.
• It is best to work compost into the soil a few weeks before seeding.
• You can mulch with compost.

How much to apply

How much compost you should apply depends on your soil test results and the requirements of your plants. As a general rule for maintaining planted beds, a layer 0.5 to 5 cm thick spread on the soil and worked into the surface is sufficient.