go! Platteland - - NO-WATER GARDENS -

I know this is heresy, but hear me out. We’ve been told by north­ern hemi­sphere gar­den and per­ma­cul­ture ar­ti­cles for so long that soil health is ev­ery­thing (it is). But we’ve also been told that healthy soil should look like the kind of nu­tri­ent-rich loams that al­most never oc­cur in na­ture on the an­cient, weath­ered ge­ol­ogy that makes up our land­scape.

The most eas­ily vis­i­ble and un­der­stood prob­lem is that wellfer­tilised or com­posted soils re­sult in rapid soft growth, de­pen­dent on sup­ple­men­tary wa­ter to sur­vive. Even if they are adapted, rapidly grown leaves don’t de­velop all the fea­tures that make lo­cal indige­nous plants able to breeze through a nor­mal dry sea­son with­out ex­tra wa­ter. These fea­tures in­clude leath­ery struc­tures that with­stand wilt­ing, the sil­very hairs and felt­ing that shel­ter the pores leaves breathe through, and even the waxy coat­ings that pre­vent wa­ter loss. You should be se­lect­ing plants bear­ing in mind such traits, and pro­mot­ing their de­vel­op­ment by pro­vid­ing the bare min­i­mum of wa­ter and nu­tri­ents your plants need.

The more im­por­tant rea­son min­i­mal or no com­post is bet­ter is en­tirely in­vis­i­ble, un­less you have a pow­er­ful mi­cro­scope. Nearly ev­ery plant has sym­bi­otic re­la­tion­ships with spe­cialised fungi called my­c­or­rhizae. This vast net­work of in­vis­i­ble fun­gal threads ex­tends the ef­fec­tive length of plant roots to many times what they have by them­selves. It is well known that this sym­bio­sis helps the plant to gather nu­tri­ents. Less well known is that my­c­or­rhizae usu­ally greatly in­crease a plant’s wa­ter up­take abil­ity and drought tol­er­ance.

So what’s the prob­lem with com­post? Well, if you raise soil phos­pho­rous and ni­tro­gen to the point where they are plen­ti­ful, plant roots sep­a­rate them­selves from the fungi, re­duc­ing their abil­ity to sur­vive dry pe­ri­ods. Com­post pro­duced by com­mer­cial or home hot-com­post­ing con­tains a lot of highly sol­u­ble and avail­able phos­pho­rous and ni­tro­gen, more than enough to dis­rupt my­c­or­rhizal de­vel­op­ment and drought tol­er­ance.

In ad­di­tion, in many sit­u­a­tions roots stay within the rich, well-wa­tered com­posted hole, not ex­tend­ing lat­er­ally into the rel­a­tively poor and dry sur­round­ing soil. Where this hap­pens, ini­tial rapid growth stops and the plant sulks. Some sen­si­ble hor­ti­cul­tural sci­en­tists have rec­om­mended against com­post­ing tree plant­ing holes for this rea­son alone.

Mulch, how­ever, can ac­tu­ally in­crease soil nu­tri­ent sta­tus to the same de­gree as reg­u­lar sur­face com­post ap­pli­ca­tion, as the soil sur­face be­comes colonised by ni­tro­gen-fix­ing bac­te­ria but with­out the de­struc­tive flush of nu­tri­ents as­so­ci­ated with com­post. So avoid the com­post, or at least go easy, and use plenty of mulch.

Of­ten, plant de­fi­cien­cies and yel­low leaves are a re­sult of a pH or nu­tri­ent im­bal­ance, and heavy feed­ing does not fix the un­der­ly­ing prob­lem. Of course, highly sol­u­ble ar­ti­fi­cial fer­tilis­ers should be used with ex­treme re­straint for all the same rea­sons.

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