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Intense heat, hot nights, and late rains that are a week or more apart. Is this the new normal for growing roses?
The heat has speeded up reflowering. I have noticed that it takes only a month from cutting back to new blooms, compared to well over two months from winter pruning to the first flush.
How does that change the way we grow roses?
Fertilising is even more important than before, otherwise the roses will quickly become starved of nutrition, which affects their growth and flowering.
Once a rose has produced flowers it prefers to go semi-dormant, producing hips (fruit) and slowing its growth for the rest of the season.
The continuous availability of nutrients, coupled with water, entices the rose to keep sprouting new shoots and flowers. Do not neglect the monthly application of Vigorosa.
Rose of the month: Impala (Korsternfue) has won awards in European Trials. Impala is a floribunda that flowers freely, growing into a dense chest-high shrub. Picture: Supplied
The hot days, especially those up to 31ºC, increase the transpiration rate and evaporation from the soil.
Giving more water in a time of water shortages doesn’t seem like a responsible response. However, there are ways to get water to the roots:
In between rainfall, harvest grey water from the shower and bath. A bucket of water per rose twice a week delivers 10 to 20 litres, which is more than adequate.
Invest in a 5,000-litre rainwater harvesting tank. One good downpour can fill a tank.
If the roses are suffering from root competition, dig them out and plant them in pots. Either sink the pots back in the ground or grow the roses as container roses.
They must be watered every day in this heat, and that is where grey water comes in. Water from the kitchen, used to wash vegetables or as rinse water can be used.
Mulch around the roses with a one to two centimetre layer of mulch. It really does keep the soil moist for longer.
Put water-starved roses in pots. Picture: Supplied
One side effect of the heat is bad infections by thrips.
Chilli thrips is a particularly vicious type that deforms buds and leaves and has a rapid breeding cycle. It takes only a week or so from the laying of eggs to two stages of larvae and new adults ready to lay eggs.
Gardeners who protected their roses by drenching with Koinor or its equivalent are not exposed to this problem. The drenching can still be done.
Badly infected parts of the roses are best cut off, put in plastic bags and thrown away. Spraying with Plant Care provides immediate relief for the roses.
When the rain does come in the form of drenching all-night rainfall, the next problem is black spot, which occurs when leaves are wet for at least six hours.
Spray as soon as the rain stops with the fungicide Chronos that prevents defoliation caused by this disease. The spray is absorbed by the leaves within minutes and cannot be washed off by subsequent rain.
If one wants a show of roses for Christmas now is the time to cut off dead flowers and even under cut stems that have sprouted already.
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