Peter Cun­dall:

Gar­den­ing guru PETER CUN­DALL says you can find out vir­tu­ally ev­ery­thing you need to know about the health of a plant sim­ply by keep­ing a close eye on its fo­liage. Learn­ing to read the signs can help pro­long — and some­times even save — the life of a plant.

Sunday Tasmanian - Tassie Living - - TASSIE LIVING -

You can learn plenty about a plant’s health by keep­ing a close eye on its fo­liage.

It pays to wan­der around the gar­den to study the fo­liage of those plants that have a vul­ner­a­bil­ity to com­mon disor­ders or nu­tri­tional de­fi­cien­cies.

Plants can­not talk, but they com­mu­ni­cate through their leaves. Once we learn this vis­ual lan­guage it en­ables us to re­spond to a range of dis­tress sig­nals by tak­ing ac­tion to rec­tify prob­lems.

Leaves are as­ton­ish­ing, liv­ing or­gans that do amaz­ing things. They are highly ver­sa­tile so­lar pan­els, able to con­vert the sun’s en­ergy so plants can draw up nu­tri­ents and mois­ture from the soil.

Leaves also col­lect and di­rect rain­wa­ter to where it’s needed, while pro­vid­ing valu­able shade around plants to re­duce waste­ful evap­o­ra­tion from the soil.

And for most plant lovers, leaves are the means by which plants dis­play the ex­tent of their health, and warn us when things start to go wrong.

When leaves flour­ish and show good, strong colours and firm tex­tures, they are telling us how healthy they are and as­sur­ing us we are prop­erly look­ing af­ter the plants.

On the other hand, when things get out of bal­ance, leaves be­come vi­tal, early warn­ing sys­tems so we can pro­vide reme­dies. Good gar­den­ing is based on un­der­stand­ing these fo­liage dis­tress sig­nals.

For ex­am­ple, when the soil around most soft-stemmed plants such as toma­toes starts to be­come too dry or ex­ces­sively sat­u­rated, they im­me­di­ately be­gin to droop. If we re­spond quickly by ei­ther ap­ply­ing wa­ter to the roots or dig­ging drainage chan­nels in time, most plants rapidly pick up again.

Other plants with thick, resinous or leath­ery leaves such as conifers, rhodo­den­drons and camel­lias can­not pro­vide the same quick in­di­ca­tion of dry or wet soil.

In­stead of wilt­ing and droop­ing, these tough leaves grad­u­ally die from the tips or mar­gins. Should these ini­tial sig­nals be ig­nored or mis­un­der­stood, it can be­come too late to do any­thing.

Oddly enough, wa­ter­logged or bonedry soil pro­duces al­most the same kind of mar­ginal leaf scorch.

Good gar­den­ing is based on un­der­stand­ing these fo­liage dis­tress sig­nals.

When acid-lov­ing plants such as rhodo­den­drons, aza­leas, camel­lias, er­i­cas, daphne and many Aus­tralian plants are mis­tak­enly limed, or have highly al­ka­line stove ash dumped around them, ad­verse ef­fects quickly show up.

This time, leaves de­scribe their dis­com­fort by los­ing colour. The youngest leaves at the tips of new growth be­gin to look very pale, while older leaves re­main green.

Some­times veins stand out bright green, while ar­eas in be­tween turn yel­low­ish-white.

The trou­ble is, these so-called acidlovers are not ef­fi­cient at tak­ing up iron, a min­eral that be­comes locked in the soil by al­ka­line con­di­tions. This is why pale new fo­liage is of­ten de­scribed as “lime-in­duced iron de­fi­ciency’’.

While we can “sweeten’’ acidic soils by ap­ply­ing lime, it is dif­fi­cult to make al­ka­line soils acidic.

So we can ap­ply a spe­cial kind of chelated iron for acid-lov­ing plants, which by­passes al­ka­lin­ity to sup­ply the iron needed. The mus­tard-coloured pow­der is cheap to buy and can be ap­plied at any time of the year.

Other plants, es­pe­cially leafy shrubs, cit­rus trees and veg­eta­bles such as bras­si­cas and sil­ver­beet, have a spe­cial need for ni­tro­gen. If they don’t get enough they don’t grow be­cause leaves re­main small, pale and can­not ef­fi­ciently har­ness the sun’s en­ergy.

This is why the soil in which leaf veg­eta­bles are to be grown should re­ceive large amounts of any kind of well-rot­ted poul­try ma­nure mixed with blood and bone deeply dug in be­fore plant­ing or sow­ing.

Cit­rus trees com­monly dis­play signs of ni­tro­gen de­fi­ciency when leaves lose the nat­u­ral, healthy green colour and grad­u­ally turn pale.

Such trees tend to re­main stunted, drop leaves and of­ten carry ex­ces­sive blos­som and lots of tiny, use­less fruit that falls to the ground while still small.

Ni­tro­gen de­fi­ciency is com­mon in free-drain­ing sandy soils or where cit­rus plants have be­come root-bound in con­tain­ers. Fo­liar feed­ing the leaves and the soil around these suf­fer­ing plants pro­duces an al­most in­stant cure.

I spray over a heav­ily di­luted high­ni­tro­gen liq­uid fer­tiliser such as fish emul­sion. It is won­der­ful to see cit­rus leaves dra­mat­i­cally re­turn to a healthy colour within a cou­ple of weeks.

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