Western Morning News (Saturday)
Chalk this way
CHALKY SOIL IS NOT A GARDENER’S BEST FRIEND, BUT WITH LIME-LOVING PLANTS AND CAREFUL PREPARATION, YOU CAN STILL ENJOY BEAUTIFUL BLOOMS
If you live in an area with a chalky landscape, you could have chalky soil in your garden. You may not see white stony lumps sticking out of the ground, but the soil is likely to be shallow and pale. Chalky soil is poor in nutrients and always “hungry”, so any manure or compost you work in soon decomposes and disappears.
All this makes for challenging gardening conditions – but with a few sensible counter-measures, there’s no need to give up hope.
Soil preparation
When you first make a new bed, spread a mixture of good topsoil (which you’ll probably need to buy in) and well-rotted garden compost or manure, up to 6in deep. Fork this into the existing soil.
Routine cultivation
The golden rule is don’t dig – it just buries what little soil there is and brings underlying chalk up to the surface. Instead, mulch beds and borders much more than usual. Spread a 2-3in layer of organic matter over the surface each spring, then again in the autumn, since by then the first lot will have vanished.
Be prepared for extra watering
Since chalk is so porous, gardens will dry out very quickly. Save rainwater in butts from guttering around the house, outbuildings and greenhouse, especially if you have metered water. If you grow thirsty plants, such as annual flowers and veggies, it may be worth putting in an irrigation system, which can be connected up to a water butt rather than a mains tap.
Planting and sowing
When preparing a planting place for a tree, shrub or climber, dig a much bigger hole than usual – roughly four times the size of the pot – and place a layer of longlasting moisture-retentive materials in the bottom.
Old woollen sweaters and cotton fabrics (no synthetics) or partially rotted organic matter will do. Then use a mixture of good topsoil and well-rotted organic matter or a proper tree-planting compost to infill the hole round the plant’s root ball.
Before planting vegetables, annuals or perennial flowers, work plenty of well-rotted garden compost (or bought-in bags of
cheap multi-purpose compost) into the soil surface. If the area has already been heavily mulched, just work a couple of trowelfuls of compost into each individual planting hole.
Before sowing seeds of veg, herbs or annual flowers directly into the ground, prepare the soil as above, but make a deep drill (a long straight groove in the soil to sow seeds into) with the corner of your hoe or rake, and sprinkle a ½in deep layer of horticultural vermiculite along the base to hold moisture in.
Sow the seeds on to this, then add a little more vermiculite to cover them.
It might seem extravagant, but this gives much better germination and bigger crops in fast-drying conditions.
Choose the right plants
Chalky soil is strongly alkaline, so don’t try growing lime-hating plants such as rhododendrons. If you want these, grow them in tubs of ericaceous (lime-free) compost and stand them on paving so their roots can’t get out through the bottom into chalky soil. Even plants that tolerate neutral soil, such as camellias, won’t thrive in chalky soil, so they too need growing in tubs.
Save rainwater to water them with, since your tap water will also be too chalky for them.
Some quite unlikely plants will also fail to thrive in chalky areas: raspberries, for instance, develop symptoms of iron deficiency. This is because on chalky soil some minerals are chemically “locked up” and therefore unavailable to plants. If in any doubt, do a soil test using a small inexpensive pH test kit, from a garden centre.
It’s much better to specialise in chalk-loving plants. These are often fairly drought tolerant, too. Good examples include aubrieta, scabious, pinks, gypsophila and pulsatilla and many types of rock plants whose natural home is in a limestone mountain, such as sempervivum.