Help your roses to keep their cool
• Hot nights bother the roses more than the heat during the day. Cool them down by watering in the early evening. The heat quickly dries off the leaves, so they won’t get fungal diseases, and there is less evaporation than watering during the day.
• A thick mulch covering the soil in a rose bed is essential when there is insufficient water, but don’t pile the leaves up against the stems. The area around the stems should be open for the water to penetrate, otherwise it is just the mulch that gets wet.
• Keep as many leaves on the bush as possible, and just break off the head of the dead roses. Check for red spider and spray as soon as you see evidence of it. A fortnightly spraying of Ludwig’s Insect Spray should keep light infestations under control if you drench the underside of the rose leaves.
To fertilise or not?
Fertilising with Vigorosa should only be delayed until the end of the month if February is extremely hot and dry, otherwise fertilise mid-month as normal. When it is hot and dry it is best to keep new growth to a minimum as it draws up extra water. Always water well after fertilising.
Gardeners always ask how much water they should give? The simplest answer is between 15 – 20 litres of water a week. This can be grey water, and if only buckets are allowed then two buckets of water a week should be enough. If you have a mist irrigation system, 5 – 10 minutes a day is not enough for the water to penetrate down to the rose roots, which are about 30cm below the surface. Rather water for one hour once a week or for 40 minutes twice a week. The type of soil also makes a difference. With heavy soil that retains water, watering can be less frequent but with sandy soil it is better to supply smaller amounts more often.
And if it rains…
• Constant rainfall is also a threat to thewell-being of the rose. Without a film of fungicide on the leaves, black spot will cause defoliation, and lots of leaves are needed during the shorter days to produce flowers. Spray with Chronos as soon as the weather allows it and repeat three weeks later.
• If you did not summer groom at the end of January, there is still time to do so. Remove diseased and twiggy growth, thin out the centre of dense bushes and cut down the very tall growers by a third.
• After a long period of rainfall it’s necessary to water the roses bushes more often to acclimatise them once again to the dry heat. Should the soil be compacted, loosen it, digging in a little composted manure if you feel it is necessary, and renew the mulch.
• Continue to groom your roses by cutting off spent flowers, disbud hybrid teas and pinch out the centre bud of the floribunda clusters.
Downy mildew in sub-tropical areas
This fungal disease is a problem in subtropical regions because it damages the capillaries, preventing normal sap flow. The flower buds don’t develop, eventually the leaves drop off, the bark bursts open and in severe cases the plants will die. Spray weekly with a broad-spectrum fungicide that contains the active ingredient mancozeb, and use a sticker like Picanta.