Tap tip Keep on wa­ter­ing plants through warm spell

The Herald Magazine - - GARDENING - DAVE AL­LAN Visit asko­r­ganic.co.uk. Fol­low Dave on Twit­ter @bod­dave

WA­TER­ING is a gar­dener’s pri­or­ity just now. I’m the last to com­plain about the best sum­mer we’ve had for years, but with­out a reg­u­lar sup­ply of life-giv­ing wa­ter our plants cer­tainly will.

To grow well, plants need air, wa­ter and nu­tri­ents. There’s a bal­ance be­tween very fine and larger pores in soil, act­ing al­most like a sponge. The small pores con­tain mois­ture and the larger ones lay on the air.

As wa­ter run out, an an­nual plant wilts and dies be­cause roots can’t spread quickly enough to ab­sorb nearby wa­ter. But peren­ni­als usu­ally de­velop a re­la­tion­ship with my­c­or­rhizal fungi which col­lect liq­uid from a larger area.

You’ll have had fewer prob­lems if, in spring, you worked to im­prove the ground with com­post and good or­ganic mulches. These keep the soil sur­face moist and pre­vent evap­o­ra­tion. But re­mem­ber: dry soil re­mains dry when mulched.

Well struc­tured moist soil eas­ily ab­sorbs rain­wa­ter, but one or two show­ers hardly af­fect sandy soil be­cause they only wet the sur­face.

Very roughly, a mil­lime­tre of rain rep­re­sents one litre per square me­tre. But it’s es­ti­mated that many plants need 2-3cm of rain ev­ery week.

This equals 25-30 litres per square me­tre. In this weather, field crops need around 10 tons of wa­ter per acre ev­ery day. So it’s hardly sur­pris­ing you see farm­ers wa­ter­ing their tat­ties even when it’s rain­ing.

All this also works for con­tain­ers. Well-struc­tured home-made com­post re­tains mois­ture for much longer than com­mer­cial com­post where wa­ter rushes through alarm­ingly quickly.

A plant saucer helps, but you may sim­ply have to wield the wa­ter­ing can more of­ten.

Soil qual­ity also af­fects nu­tri­ent lev­els. In 2008, a study com­pared the ef­fect of dry­ing soil on unim­proved and grass­land treated with ar­ti­fi­cial fer­tiliser. Ni­tro­gen lev­els didn’t change in the for­mer, but sig­nif­i­cant amounts of sol­u­ble ni­tro­gen were leached away from the lat­ter.

THE sci­en­tists found the larger com­mu­nity of mi­cro-or­gan­isms, es­pe­cially fungi, in un­af­fected ground ex­plained this. So, de­pend­ing on your soil, you may need to keep nu­tri­ent lev­els topped up in pots and open ground while plants are de­vel­op­ing.

This es­pe­cially ap­plies to an­nual fruit and veg.

And as I write, fore­cast­ers are pre­dict­ing this won­der­ful spell of weather will con­tinue, so keep on wa­ter­ing. It’s frankly as­ton­ish­ing

how much wa­ter plants need. And al­though you can help re­duce evap­o­ra­tion, you can’t stop plants cool­ing them­selves by tran­spir­ing.

The larger the leaf, the more a plant tran­spires, so a cour­gette or cu­cum­ber is a wa­ter junkie. Nar­row-leafed rose­mary and dianthus have modest re­quire­ments, so you should use the head when wa­ter­ing and only give to needy cases.

So what’s the best way of wa­ter­ing? When run­ning a demon­stra­tion gar­den, we tried lots of dif­fer­ent sys­tems for con­tain­ers; they helped but didn’t per­form as well as man­u­fac­tur­ers claimed.

I’m con­vinced hand wa­ter­ing is best. You wa­ter ac­cord­ing to the va­ri­ety and a sim­ple fin­ger probe shows when it’s needed. You en­joy the plants by get­ting up close, tie in or dead­head, and spot prob­lems at an early stage. A cou­ple of good soaks a week works for many pots.

In the open ground a leaky hose works well, even though plants at the bot­tom of a slope get more wa­ter than those at the top.

But if you have pli­able ir­ri­ga­tion tub­ing, you’ll get a more even dis­tri­bu­tion by weav­ing it through a bed in S-shapes.

Al­ways use a pres­sure re­ducer with mains wa­ter. My gen­tle grav­ity-fed spring wa­ter needs no such de­vice.

Oth­er­wise a spray gun on the hose is the an­swer. Salvia nemorosa Caradonna. A peren­nial salvia with rich pur­ple flow­ers in spikes that last for much of the sum­mer. Its nar­row, grey-green leaves en­sure that, once es­tab­lished, it is drought-tol­er­ant.

Plants need a reg­u­lar sup­ply of life-giv­ing wa­ter, es­pe­cially dur­ing fine sum­mer weather

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