Su­per­charge your soil

There’s more to gar­den soil than meets the eye. Alan Titch­marsh shows how to get yours into shape for bor­ders that are burst­ing with healthy plants

Gardeners' World - - Contents -

Healthy soil means healthy plants. Fol­low Alan’s guide to boost yours

Spend as much on the hole as you do on the plant.’ It’s an adage we would all do well to re­mem­ber from time to time – a re­minder that ev­ery plant is only as good as the soil it is planted in. But soil is bor­ing – it’s brown or grey and it just sits there. All of which may be true, but with­out it we gar­den­ers would be, in com­mon par­lance, stuffed. But what ex­act ly is soi l? Soi l is, ba­si­cally, ground up rock mixed with rot­ting or­ganic mat­ter. The na­ture of the rock, the size of the par­ti­cles, the num­ber of min­er­als that are present and the com­po­si­tion and amount of or­ganic mat­ter it con­tains is what makes soil so vari­able. As far as the gar­dener is con­cerned we are look­ing for some­thing that will pro­vide our plants with firm an­chor­age, nu­tri­tion, suf­fi­cient wa­ter re­ten­tion and ef­fi­cient drainage. Achiev­ing that in our gar­dens and al­lot­ments is down to us as much as na­ture. A patch of earth that is dis­turbed by cul­ti­va­tion and in which we grow plants on an in­ten­sive scale needs rather more in the way of care and at­ten­tion than a patch of undis­turbed coun­try­side, where the cy­cle of na­ture can achieve a bal­ance and where hu­mus (the nat­u­ral or­ganic con­tent of soil) is al­lowed to build up with­out in­ter­fer­ence. Good soil is a liv­ing thing, teem­ing with micro­organ­isms, from bac­te­ria to fungi. The ad­vent of an­ti­sep­tic wipes has led to many peo­ple imag­in­ing that all bac­te­ria are bad, but with­out the ex­is­tence of ‘good’ bac­te­ria we as hu­mans would fail to sur­vive and soil would be a poorer sub­stance in which to grow plants. The in­ter­ac­tion of bac­te­ria and fungi, in­clud­ing my­c­or­rhizal fungi – which have a sym­bi­otic re­la­tion­ship with plant roots and are ben­e­fi­cial to growth – is vi­tally im­por­tant. Many fungi are nat­u­rally present in soil, but you can help new plant s de­velop th­ese benef icial re­lat ion­ships by dust­ing both the roots and plant­ing hole with my­c­or­rhizal fungi. It is widely avail­able to gar­den­ers now at gar­den cen­tres and nurs­eries where it is sold in sa­chets and pack­ets. The eas­i­est to find is the brand Root­grow (which trips off the tongue a lit­tle more eas­ily than my­c­or­rhizal fungi).

The im­por­tance of nu­tri­ents

Plants need three main nu­tri­ents to thrive – ni­tro­gen, which en­cour­ages leaf and shoot growth, phos­phates, which pro­mote root de­vel­op­ment, and potash, which is nec­es­sary for f lower and fruit de­vel­op­ment. They are des­ig­nated as

Good soil is a liv­ing thing, teem­ing with micro­organ­isms, from bac­te­ria to fungi

Or­ganic fer­tilis­ers feed vi­tal bac­te­ria as much as the plants, and keep the soil health­ier than in­or­ganic fer­tilis­ers

N, P and K on pack­ets of fer­tiliser, which show the ra­tio in which they are present. Aside from th­ese, there are some vi­tal trace el­e­ments that are needed in smaller and vari­able quan­ti­ties for plants to be healthy: el­e­ments such as mag­ne­sium, cal­cium, iron, boron, zinc and the strange­sound­ing molyb­de­num. The sim­plest way to en­sure your soil has suf­fi­cient quan­ti­ties of th­ese trace el­e­ments is to reg­u­larly en­rich it with ‘gen­eral’ fer­tiliser and well­rot­ted or­ganic mat­ter.

Acid or al­ka­line

Soil acid­ity – mea­sured on the pH scale – will also af­fect plant growth. Acid soil has a pH be­low 7.0, al­ka­line soils – those con­tain­ing chalk and lime­stone – have a pH of 7.5 or above. The leaves of rhodo­den­drons, aza­leas, pieris, camel­lias and other lime-haters turn yel­low when the plants are grown in al­ka­line soil be­cause they, as a group, nat­u­rally grow in acid soils and are un­able to ex­tract iron from those of an al­ka­line na­ture. We avoid grow­ing them on chalky soil for that rea­son. If you’re grow­ing on soil that is only slightly acid, it is a good idea to wa­ter on se­questered iron to help keep them healthy and green (se­questered sim­ply means the iron is in a form they find eas­ier to ab­sorb). Reg­u­lar crop­ping, heavy rains and con­stant cul­ti­va­tion wi l l, over time, de­plete the soil of nu­tri­ents, which is why it is im­por­tant to feed cul­ti­vated soil reg­u­larly – ap­ply­ing a gen­eral fer­tiliser each spring, just at the time when plants will be call­ing for nu­tri­tion. Soil that is de­pleted of nu­tri­ents will pro­duce fee­ble plants that are starved of nu­tri­tion and whose growth and gen­eral health are poorer as a re­sult.

Feed­ing the soil

Or­ganic fer­tilis­ers, such as blood, fish and bone, must be bro­ken down into an ab­sorbable form by soil bac­te­ria be­fore they can be utilised by plants, and as such have the ad­van­tage of feed­ing the vi­tal bac­te­ria as much as the plants and keeping the soil health­ier than in­or­ganic fer­tilis­ers, which can be ab­sorbed by the plants as soon as they go into so­lu­tion with the mois­ture in the soi l. In­or­ganic fer­tilis­ers may feed plants but they do not feed the soil. But if plant nu­tri­ents are the ‘vi­ta­mins’ nec­es­sary for growth, then the meat and two veg – the pro­tein and the

Worms are to be en­cour­aged for their abil­ity to mix in or­ganic mat­ter and im­prove soil struc­ture

car­bo­hy­drates – come from or­ganic mat­ter, which im­proves soil struc­ture in a way that pow­dered, gran­u­lar or liq­uid fer­tiliser can­not. Well-rot­ted bulky or­ganic mat­ter, in the form of ma­nure or gar­den com­post, will bind to­gether a thin, sandy soil, help­ing it to hold on to both mois­ture and nu­tri­ents. It will also open up a clay soil that is plas­tic and in­tractable thanks to the par­ti­cles be­ing so small that they bind to­gether tight ly, im­ped­ing drainage and mak­ing cult iva­tion di f f icult . Leaf­mould, which is made from slowly de­cay­ing leaves, will have a sim­i­larly ben­e­fi­cial ef­fect on soil struc­ture, but adds lit­tle in terms of nu­tri­ents.

Keeping it healthy

Or­ganic mat­ter rots down over time and so needs to be reg­u­larly ap­plied ( ide­ally an­nu­ally) to keep soil healthy – bac­te­ria and fungi thrive on its pres­ence – but on clay soils it is also worth adding sharp grit­sand, which is longer-last­ing in terms of im­prov­ing drainage. Worms do their bit here, too, and are to be en­cour­aged for their abil­ity to mix in or­ganic mat­ter and im­prove soil struc­ture and drainage. Yes, they are a pain on the lawn where their casts cause prob­lems, but else­where they do much good, so learn to live with them! There is also a host of other soil ad­di­tives avail­able to the gar­dener, such as vol­canic rock dust, which can be used to add min­er­als and trace el­e­ments, and biochar – spe­cially pro­duced char­coal that is said to sta­bilise the earth’s car­bon re­sources and im­prove soil’s abil­ity to re­tain wa­ter and nu­tri­ents. What is in­dis­putable is that good drainage, es­sen­tial nu­tri­ents and plenty of or­ganic mat­ter are the ‘big three’ that will make all the dif­fer­ence when it comes to grow­ing strong, healthy plants, with plenty of fruit and flow­ers.

Oc­to­ber 2017

Adding my­c­or­rhizal fungi to roots boosts plant es­tab­lish­ment and growth Col­lect fallen leaves to make leaf­mould to boost your soil’s struc­ture

Use a pH test kit to find out if your soil is acid or al­ka­line

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