Unlock the nutrients in clay
Squelching about in the muddy clay soil might be fun when five, but not fifty five, or at any age when you decide to get serious about planting and gardening. Discovering your bit of paradise is covered in soggy, boggy clay is a moment for many New Zealand gardeners. But should it be?
Clay soil is actually packed full of beneficial nutrients that your plants will love, and it retains moisture, which plants also need to thrive. The problem lies with the fine texture and dense structure of the soil. The very small particles stick together, locking in those lovely nutrients and making them unavailable to plants. The density of the soil means air and water can’t move freely through the soil, this resistance causes the water logging and slow drainage.
Two things to do when gardening in clay soil
There are two key things to do when gardening in clay soil.... and you need to do both!
- Short term : Modify some of the soil to facilitate planting
- Long term: Improve the texture of the remaining garden soil
Improving soil takes time and there is no magic bullet so if you are keen to get going, start by modifying soil in key areas, such as planting holes and vegetable gardens.
- Creating raised or mounded garden beds is a great way to facilitate planting in water-logged soils as it helps to keep roots clear of very wet soil. This is also a great way to get vegetable gardens sown in spring, when clay soils are notoriously slow to warm up.
- For larger projects that need to get underway, create modified, individual planting holes. Dig these to around twice the width and depth of the root ball of the seedlings, then crumble some of the clay and put back in the hole, mixing it with good quality commercial soil mix. It’s vital the seedlings are planted at the same depth as they were in their nursery pot to avoid collar rot.
Improve planting niches, but don't stop there.
Most plants will outgrow these lovely planting niches you have created, and unless you have chosen plants that have strong enough root systems to make their way down through clay soils and then cope with the water logged conditions, you also need to work on long-term improvements on the surrounding soils, which will aid future planting projects.
- Adding organic matter such as mulch, compost, manure or straw to add humus is a great start. Add about 7 -10cm lightly mixed into the top layer of soil to break it up, going about as deep as the head of the spade. Repeat this overtime as the mulch layers break down and become incorporated into the soil. This helps lighten the soil structure, resulting in better drainage. Overtime move to a ‘no-dig’ system as it doesn’t disturb the work of beneficial microorganisms and insects.
- If digging isn’t your thing, or if the gardens are too established to dig over as described above, just layer organic mulch on top of the soil. This also helps prevent clay soils becoming hard and cracked in the dryer months. Make it around 5 - 10cm thick, and just keep adding layers as it breaks down or gets worked into the soil by those industrious worms and microorganisms.
- Topical applications of Gypsum have long been the go-to for gardeners (including this one) desperate for help with breaking down those sticky clay particles. It is an environmentally friendly, natural mineral that, when it dissolves, slowly releases equal amounts of calcium and sulphate into the soil. If the soil is a very heavy clay, more than one application may needed.
Key things for improving clay soil
As you go about improving clay soil, remember these important things:
- Clay soil compacts easily, which makes it heavier and exacerbates drainage problems.
- Never dig or plant in clay soil when it is wet or dry. Damp is best.
- Keep off clay soil when it is wet, use boards or pavers to distribute your weight if you are laying mulch.
- Autumn is a great time to dig and incorporate organic matter.
- In colder areas, after autumn digging leave the soil surface in ridges over winter, so frost can get in and break up the clumps.
- Plant woody shrubs and trees on soil mounds to encourage run off and help keep roots clear of very wet soil.
- Don’t add sand to clay soil, it turns it rock hard
Lots of plants flourish regardless.
If it all sounds like too much hard work, don’t despair.... instead opt for plants that will thrive in clay soil.
For shrubs and perennials - the list includes many old favourites;
- Cranesbill geraniums
- Clivia, to name a few.
Looking for trees and shrubs try;
If natives are more up your garden alley consider;
- Cabbage trees