Peter Cun­dall:

When it comes to win­ter wa­ter­ing less is more

Sunday Tasmanian - Tassie Living - - TASSLE LIVING -

It’s easy to be tricked into think­ing that plants show­ing signs of wilt­ing fo­liage must need a drink

The ma­jor­ity of so-called plant dis­eases are re­ally dis­or­ders ag­gra­vated or caused by stress. As tem­per­a­tures drop and soils cool, most or­na­men­tal plants, in­clud­ing ev­er­greens, take the hint and take a rest. Dur­ing this pe­riod, lit­tle nutri­tion is re­quired and wa­ter­ing re­duced.

As win­ter ap­proaches, many in­sect pests seem to dis­ap­pear for a while. Some die after de­posit­ing over-win­ter­ing eggs while oth­ers form co­coons and go into win­ter dor­mancy. Plant dis­or­ders are dif­fer­ent. Cool con­di­tions dur­ing late au­tumn and win­ter of­ten bring out a range of new ones.

The sin­gle big­gest cause of house­plant death dur­ing win­ter is mol­ly­cod­dling, es­pe­cially through over-wa­ter­ing. It is easy to for­get that these plants have vir­tu­ally stopped grow­ing. So dam­age is done when we thought­lessly con­tinue with sum­mer habits by giv­ing them daily drinks they can­not take up.

This is why win­ter pot­ting soils of­ten be­come so badly wa­ter­logged they start to stink. This also in­di­cates that soils are turn­ing toxic.

Over-wet con­di­tions cause nor­mally friendly bac­te­ria and soil fungi to go feral and start at­tack­ing plant roots. This is the real rea­son why over-in­dulged plants of­ten look sick or col­lapse dur­ing win­ter.

Too of­ten, prob­lems of wa­ter-logged pot­ting soil are made worse when more wa­ter is added. It’s easy to be tricked into think­ing that plants show­ing signs of wilt­ing fo­liage must need a drink. When ex­tra fer­tilis­ers are also ap­plied, it can lead to dis­as­ter. This is the equiv­a­lent of force-feed­ing some­one dy­ing from pneu­mo­nia with steak and kid­ney pud­ding.

Over-wa­ter­ing of pot plants can be avoided. Stick a fin­ger into the soil ev­ery now and then. It’s a sim­ple way of check­ing mois­ture lev­els. Pot­ting soil in win­ter is best kept slightly moist, es­pe­cially in cool dis­tricts. Drip trays be­neath pots must never be al­lowed to re­main filled

with wa­ter. That’s also ask­ing for root-rot.

Most house­plants, es­pe­cially cy­cla­mens which have large, mois­ture-hold­ing, bulb-like corms, or or­chids with thick swollen roots, pre­fer soil to be­come al­most dry be­tween each wa­ter­ing.

In the garden the sit­u­a­tion is dif­fer­ent again. In cool dis­tricts, nor­mal win­ter rain­fall is enough to keep most plants happy, pro­vided drainage is good. In heavy, clay soils, plants with shal­low, com­pact roots such as rhodo­den­drons, aza­leas and some conifers need spe­cial care be­cause wa­ter­log­ging is al­ways a win­ter dan­ger. Conifers rarely show they are suf­fer­ing wet-feet un­til it is too late. That’s when nee­dles go brown and start to fall. All we can do is dig them out be­cause few conifers can be re­vived after be­ing se­ri­ously wa­ter­logged.

Rhodo­den­drons and aza­leas give a clear warn­ing when they are in strife. Should soil re­main sat­u­rated where drainage is poor, leaf-edges take on a scorched ap­pear­ance. This is mar­ginal leaf-scorch and we must act quickly to save dis­tressed plants. They are best lifted, dead roots scraped off, pruned lightly and re­planted, this time into low mounds, even on the same spot. They are even safer if trans­planted to new po­si­tions where drainage is good.

Just the same, signs of mar­ginal leaf scorch can also be mislead­ing. If these plants have re­cently en­dured a long, dry sum­mer with lim­ited wa­ter, many leaves show sim­i­lar symp­toms with leaf-tips dy­ing back and go­ing brown.

Chilly soils also cause nu­tri­tional de­fi­cien­cies in many plants which show up in leaves. These min­eral short­age symp­toms can ap­pear, even when soils are fer­tile. Low tem­per­a­tures keep many min­eral nu­tri­ents locked up and plants are un­able to take them up.

Cit­rus trees such as le­mons, cumquats and grape­fruits of­ten dis­play pale or mot­tled leaves dur­ing win­ter. These are typ­i­cal signs of ni­tro­gen, iron, mag­ne­sium or zinc de­fi­cien­cies, all el­e­ments needed by cit­ruses. Fo­liar feed­ing, that is spray­ing leaves with a weak, min­eral-rich nu­tri­ment at any time of the year pro­vides good re­sults. How­ever, the real ben­e­fits come from residues that drip down over root-zones after fo­lia feed­ing.

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