Down to earth

Our gar­dens will only ever be as good as the soil that sup­ports them.

NZ Gardener - 365 Days of Flowers - - Practical gardening -

Be­fore you set out to cre­ate a new gar­den, find out what soil type you have. Is it acid or al­ka­line, clay or sand? Take the time to pre­pare the proper soil en­vi­ron­ment be­fore plant­ing. Good soil prepa­ra­tion is the most im­por­tant thing you can do for your flow­ers.

ACID/AL­KA­LINE?

Get a test­ing kit to re­veal your soil's ph. Acidic soils (ph 0-7) tend to be low in phos­pho­rous; al­ka­line soils (ph 7-14) may lack iron and man­ganese. Most plants will grow in ei­ther soil, but some are suited only to a par­tic­u­lar ph level. Rhodo­den­drons and camel­lias like acid soil.

CLAY OR SAND?

Roll a hand­ful of damp soil be­tween your fin­gers. If it forms a solid sausage, you have clay soil. If it feels gritty and falls apart, it is mostly sand. You can also put a lit­tle soil in a jar of water and shake it. If the water is clean on top af­ter an hour, you have sandy soil.

IM­PROVE CLAY

Add grit or coarse sand to clay soil to im­prove drainage. Don't add fine sand; it can make clay soils worse be­cause it blocks soil pores. Add lime or gyp­sum. Add or­ganic mat­ter; it opens up a soil's struc­ture and im­proves drainage. Mulch with com­post in late spring.

PLANTS FOR SAND AND CLAY

Sandy soils drain so well that plants never suf­fer from cold, wet feet. The down­side is in sum­mer, they can't hold on to mois­ture, so only very drought-tol­er­ant plants sur­vive. They're of­ten poor in nu­tri­ents, but they warm up quickly in spring. Feed sandy soils with slow-re­lease fer­tilis­ers such as or­ganic blood and bone rather than highly sol­u­ble store-bought va­ri­eties, or potash and am­mo­nium ni­trate, which will quickly be washed away and may go on to pol­lute our nat­u­ral wa­ter­courses.

Deep-rooted plants that can probe and quest for mois­ture are go­ing to do bet­ter in sandy soil than shal­low, fi­brous-rooted sub­jects. Plants from an­cient soils and arid cli­matic zones, such as South African protea or Aus­tralian gre­vil­lea, will love the poor con­di­tions and arid out­look, not to men­tion other Mediter­ranean cli­mate clas­sics such as Cal­i­for­nian lilac (cean­othus), laven­der and cis­tus. Any shrub with a grey leaf, such as Rus­sian sage (perovskia) or artemisia, will thrive in sandy soil too.

Most clays in this coun­try are slightly acidic and con­tain a good level of nu­tri­ents. Tough tra­di­tional herba­ceous plants such as aster, as­tran­tia, canna, clivia, gera­nium, paeony, phlox, heme­ro­cal­lis (daylily) and lupin will do well. In heavy soil they won't spread so fast and will need di­vid­ing less of­ten. Heavy soils also tend to har­bour slugs – that's why they are not great for grow­ing fussy and del­i­cate plants such as del­phinium and echi­nacea. The clas­sic shrub for heavy ground is the rose, but hy­drangea, spirea, philadel­phus, weigela and vibur­num will do well too. Good bulbs for clay in­clude most nar­cis­sus, schizostylis, zephyran­thes and slen­der reed-like Onixo­tis tri­que­tra, with its star­tling win­ter flow­ers.

Good or­ganic gar­den soil is filled with air that plant roots need, and it has plenty of min­er­als es­sen­tial for vig­or­ous growth.

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