Peter Cun­dall: Tips for help­ing to stop the rot, such as pow­dery mildew, over sum­mer

Al­though sum­mer is one of the harsh­est sea­sons of all on plants, a few timely in­ter­ven­tions can make all the dif­fer­ence to a bloomin’ mar­vel­lous gar­den, ac­cord­ing to PETER CUN­DALL

Sunday Tasmanian - Tassie Living - - NEWS - with Peter Cun­dall

Sum­mer is al­ways a cru­cial part of the grow­ing sea­son be­cause plants in all parts of the gar­den are not only grow­ing strongly, but flow­er­ing or fruit­ing steadily. It’s when plants receive an un­ex­pected check in growth in sum­mer that we need to act quickly to rec­tify the prob­lem.

Pow­dery mildew is a fun­gal dis­ease that sucks vi­tal­ity from plants. For ex­am­ple cer­tain roses are more vul­ner­a­ble than oth­ers. When the at­mos­phere around the fo­liage re­mains stag­nant due to over­crowded branches and sun­light is also re­stricted, pow­dery mildew can strike. Im­me­di­ately prun­ing off all dis­eased leaves and branches then open­ing up the plants for good air cir­cu­la­tion stops most fun­gal dis­eases de­vel­op­ing. Any roses in too much shade – they all need full sun – are a tar­get for pow­dery mildew so be pre­pared to trans­plant them to a sunny spot next win­ter.

Dahlias also need as much sun­light as pos­si­ble. When pow­dery mildew moves in, spray­ing is a waste of time where plants are in shade. The an­swer is to lift tu­bers in late May and re-plant the fol­low­ing spring in the sun­ni­est place you can find – even in large pots if nec­es­sary.

Rust dis­ease is an­other sum­mer prob­lem. Hol­ly­hocks and pelargo­ni­ums are among the most com­mon plants in­fected, with the first signs as pale, raised spots on the un­der­sides of older leaves. Pull off all dis­eased fo­liage and take well away for quick con­trol of rust with­out spray­ing, but act fast.

Har­le­quin bugs are now at­tack­ing plants, es­pe­cially fruit and toma­toes. They form large colonies, not only feed­ing off juices, but de­stroy­ing and taint­ing flavour. We see the ev­i­dence as pale, yel­low­ish mar­gins just be­neath the skins of toma­toes. The black bugs, each with an orange mark be­hind the head, con­gre­gate and breed on mal­low weeds, hol­ly­hock, hi­bis­cus and lavat­era. Most sprays are

Any roses in too much shade – they all need full sun – are a tar­get for pow­dery mildew so be pre­pared to trans­plant them to a sunny spot next win­ter

de­flected by a wa­ter-re­pel­lent waxy coat, so spe­cial mea­sures need to be taken to de­stroy har­le­quin colonies.

They gather to­gether young and old every evening – usu­ally in crevices in wooden fences or around tim­ber beams sup­port­ing cor­ru­gated iron roofs of gar­den sheds. They emerge, just af­ter sun­rise some­times in enor­mous clus­ters to briefly bask in the warmth on fences, walls and wooden posts be­fore dis­pers­ing to con­tinue feed­ing. This is when they are most eas­ily and safely de­stroyed by spray­ing the clus­ters with an ex­tra-strong so­lu­tion of house­hold de­ter­gent. This pen­e­trates the pro­tec­tive waxy coats, en­ters their breath­ing tubes at the sides of their bod­ies and they die by suf­fo­ca­tion.

Some peo­ple clean the ash from wood heaters dur­ing win­ter, then mis­tak­enly dump the stuff around or­na­men­tal plants. Un­for­tu­nately wood ash is highly al­ka­line and when spread around aza­leas, rhodo­den­drons, camel­lias and er­i­cas – all acid-lovers - it acts like lime, lock­ing up iron in the soil and caus­ing chloro­sis. The youngest leaves go pale and the plants re­main stunted. The only so­lu­tion is to ap­ply chelated iron which by-passes the al­ka­lin­ity created by the ash. The best place for wood ashes is in the vegie patch around lime lovers such as bras­si­cas, beans, onions and cel­ery.

Blood and bone is an ideal or­ganic fer­tiliser to ap­ply right now – al­ways af­ter wa­ter­ing. It sup­plies cal­cium, some phos­pho­rus and slow-re­lease ni­tro­gen. Min­eral sup­ple­ments such as potas­sium and mag­ne­sium can be added to make a com­plete sum­mer fer­tiliser for most plants. I add a good hand­ful of sul­phate of potash and a heaped dessert spoon­ful of Ep­som’s salts to every 10kg of blood and bone. This mix is eas­ily scat­tered around all shrubs, cit­rus trees peren­ni­als and leaf veg­eta­bles and wa­tered in.

Camel­lias need pro­tec­tion from per­sis­tent winds and long pe­ri­ods of strong sun­light. Bleach­ing of the most ex­posed leaves is a com­mon sum­mer dis­or­der. Growth also be­comes stunted and late win­ter flow­er­ing can be dis­ap­point­ing. The good news is that badly-sited, over-ex­posed camel­lia bushes can be lifted and moved to more shel­tered spots at any time of the year – even now. But be sure to wa­ter deeply first to keep root-balls sticky and in­tact dur­ing the move and al­ways soak new plant­ing holes first.

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