build­ing healthy soil

Three of the best things you can do for your gar­den this win­ter.

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Great soil is a gar­dener’s best friend. Hid­den be­low ground level, it’s too of­ten forgotten – un­til you won­der why your plants are fail­ing to thrive! The an­swer lies in or­ganic mat­ter.

Or­ganic mat­ter is the stuff that makes top­soil black. It’s where earth­worms and vi­tal micro­organ­isms live and work. For a thriv­ing pro­duc­tive gar­den we can’t have too much of it. The more we can do to bol­ster the or­ganic mat­ter in our soil the bet­ter our gar­dens will be. Here are three great jobs for win­ter week­ends that you won’t re­gret spend­ing time on.

1 Make com­post

Buy­ing com­post, in bags or by the trailer load, is money well spent. But you can make your own for free.

When the leaves fall from the trees con­sider them a gift! Rake them up or mow them up with grass clip­pings then pile them on the com­post heap, in a cage made from wire netting, or into bags with holes for air move­ment. Six months later you will have beau­ti­ful black com­post for your gar­den.

Com­post of course can be made from any re­cy­cled or­ganic mat­ter. The se­cret to mak­ing good com­post lies in get­ting the right bal­ance of ni­tro­gen (soft ‘green’ ma­te­rial) and car­bon (coarse ‘brown’ ma­te­rial). Too much green, and it will be slushy and smelly. Too much brown and it will not gen­er­ate enough heat.

Start with a ‘brown’ layer of coarse twigs for air cir­cu­la­tion. Then add a ‘green’ layer (e.g. kitchen food scraps, grass clip­pings) about 20-30cm deep. Then a 50cm layer of brown ma­te­rial (shred­ded stalks and twigs, dead leaves, straw, shred­ded pa­per etc). Next, a sprin­kling of blood and bone and lime is an op­tional ex­tra to speed up the process. You could also add an­i­mal ma­nure or a com­post ac­ti­va­tor.

Re­peat the lay­ers un­til the bin is full. Lay­ers sink as they de­com­pose. Cover the heap to keep the heat in and rain out. Turn­ing the com­post ev­ery few weeks with a gar­den fork will fur­ther speed up the de­com­po­si­tion.

2 Sow a cover crop

It might sound crazy to sow a crop of plants and then kill it just when it starts to look beau­ti­ful, but this is one of the very best things you can do for your soil. Also known as green ma­nure, a cover crop is sown in au­tumn or early win­ter and then chopped and dug into the soil in spring.

Cover crop­ping im­proves mois­ture re­ten­tion and drainage. As well as pro­vid­ing bulk ni­tro­gen, it will bring deep min­er­als to the sur­face. It also blocks weed growth and protects the soil in heavy rain. Sow­ing a cover crop will make the soil much eas­ier to dig in spring. As the roots grow over win­ter they keep the soil aer­ated and re­duce com­paction. Cover crops also help break dis­ease cy­cles.

Cover crop seed is sold in bulk packs. In New Zealand gar­dens the tra­di­tional cover crops are lupins and mus­tard. Wheat, bar­ley or oats may also be used to add or­ganic bulk. Or a mix­ture may be sown. Mus­tard helps against prob­lem­atic soil fungi but should not be sown in soil that has just had a bras­sica crop. Lupins add ex­tra ni­tro­gen via spe­cial ‘ni­tro­gen fix­ing’ bac­te­ria in their root nod­ules which take ni­tro­gen from the air and con­vert it into a form that plants can use.

Lupin is best dug in just be­fore flow­er­ing. If you want to see the pretty blue flow­ers you can dig it in just af­ter flow­er­ing, but flow­ers will take some of the ni­tro­gen from the soil. You will also need to fac­tor in time for the green mat­ter to break down be­fore you plant your spring crops. Al­low at least three weeks, ide­ally six. When dig­ging in your cover crop, it’s a good idea to take the op­por­tu­nity to dig in lime and an­i­mal ma­nure at the same time.

3 Lay mulch

Mulch is a blan­ket of or­ganic mat­ter cov­er­ing the soil sur­face. This not only saves time and en­ergy spent weed­ing and wa­ter­ing, but does won­ders for your soil as it breaks down. Ev­ery time you add an­other layer of or­ganic mulch you are re­plen­ish­ing the soil and ben­e­fit­ing fu­ture plant growth. Or­ganic mulches in­clude straw, bark, pine nee­dles, leaves, wood chip, com­post and saw­dust.

Be­fore lay­ing mulch, clear the weeds, wa­ter and feed with slow re­lease fer­tiliser, blood and bone or sheep pel­lets. A thick layer of news­pa­per un­der the mulch acts as an ex­tra weed bar­rier. Make sure you wet it thor­oughly. Spread mulch about 5-8cm thick, tak­ing care not to pile it up around plant stems. In win­ter, mulching helps in­su­late roots from the cold.

A cover crop is a great way to rest and re­vive a patch of soil af­ter in­ten­sive vege grow­ing - restor­ing or­ganic mat­ter, earth­worms and ben­e­fi­cial micro­organ­isms.

Lupin

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