Characteristics of clay
You know you have clay soil if:
- the soil is sticky and difficult to dig
- digging often results in huge clods that are hard to break up
- the soil is heavy and slow to warm up in spring
- during a stretch of dry weather, the surface hardens and cracks
- the soil is slow to drain
1. Clay soil is easily compacted. Avoid walking on cultivated soil, especially when it’s wet, or compressing it with heavy equipment. Digging wet clay also compromises its structure and will set back your efforts to improve it.
2. Amend clay soil by adding plenty of organic material, such as well-aged compost, sawdust (but not from pressure-treated wood), composted manure or leaf mould (partially decomposed shredded leaves). Coarse materials are better than fine ones. Do this repeatedly and as often as possible. For example, when making a new bed, spread several centimetres of organic material over the area and dig it in at least 20 centimetres deep. When moving or adding new perennials to an existing bed, throw a shovelful of compost into the planting hole.
Organic materials prompt mineral particles such as clay to come together in clumps, called aggregates. The various sizes and shapes of these clumps help form larger pore spaces, which creates more room for oxygen and water to move around plant roots. Organic materials also attract earthworms and micro-organisms that will munch and digest their way around the soil, loosening up its structure even further.
3. Hand digging is preferable to using a tiller, which pulverizes soil into too fine a texture. Digging with a shovel leaves clumps of various sizes that allow a better exchange of oxygen in the plants’ root zone. Dig down at least 20 centimetres when amending. Fall is the best time because soil is usually drier than in spring. Leave rough clods to allow snow to further break down the soil.
4. A five- to eight-centimetre layer of organic mulch, such as shredded bark or leaf mould, helps keep the soil from forming a crust. It also ups the quotient of organic matter.
5. Adding sand can make matters worse; to have a positive effect, it must be coarse builder’s sand (various-sized particles; not horticultural or play type) and copious amounts are needed—at least one part coarse sand, one part organic matter and one part existing soil. Adding too little or too fine a sand creates the perfect conditions for making bricks!