Clay soil: 5 tips for making your garden flourish with heavy soils
Clay soils get a bad rap. In winter they are sodden and easily compacted. They take longer to warm up in spring and by summer they've turned to concrete. The fine particles stick together so there is poor drainage and lack of aeration leading to poor root growth.
Back-breaking and expensive suggested solutions to improving heavy clay include replacing it all with friable loam or digging in trailer loads of sharp sand and gravel.
But the news is not all bad for gardeners. Heavy clay is often fertile as nutrients aren't lost by leaching and it retains moisture in dry weather. With a bit of knowhow gardens can flourish on clay without breaking the bank or your back.
Five ways to garden on clay soil
1. Mulch, mulch, mulch
Adding compost, manure or any sort of mulch from bark shreds to coffee grounds adds humus. Clay particles clump around the humus so aeration and drainage improve. Fork lightly into the top layer of soil or let the worms do the work for you. Keep adding mulch layers as they break down and become incorporated into the soil.
Adding gypsum aggregates clay particles too. Don't add it every year though as it can increase salinity.
3. Rise above it
Plant trees and shrubs on low mounds where they'll get the drainage they need but still have access to moisture in the clay soil below. Grow veges in raised beds or no-dig gardens avoiding the clay beneath.
4. Avoid compaction
Walking on sodden clay soil or trying to dig it when wet just makes the problem worse. If necessary lay planks over the beds to distribute weight over a greater area. Or use stepping stones so only spots not needed for planting are compacted.
5. Grow clay tolerant plants
Tough herbaceous plants like clivia, hostas, paeonies and daylilies thrive in slightly acidic and nutrient rich clay soils. As a bonus they won't spread so fast so need dividing less often. Roses, hydrangea, philadlelphus and viburnum will do well too. Many natives don't mind getting occasional wet feet. Try pittosporum, pseudopanax, flax, oioi and manuka. In the vege patch grow a crop of potatoes which will break up the soil and make it more friable to the advantage of the next vegetables to be planted in that spot.
- NZ Gardener