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Brassicas (plants of the cabbage family) planted in late December or during January will now need protection from white butterfly caterpillars and grey aphids. A dusting of derris dust once a fortnight or after rain will kill caterpillars.
An alternative is to make lightweight frames and cover them with plastic mesh of the type sold to protect strawberries. The frames prevent white butterflies from landing on the plants and laying their eggs. Grey aphids are most effectively controlled by insecticides or by planting pyrethrum (Chrysanthemum cinerarifolium) as close as possible to brassicas.
Onions are ready for harvesting once the leaves start turning brown or begin drying up. Pull out onions and place in a sunny place to dry completely. Store for use during winter by stringing in bunches or placing in a single layer on a wire netting rack in a dry, airy place where they get some light.
Freesias, grape hyacinths (Muscari botryoides and M. armeniacum), fritillaries and bulbous irises (Iris reticulata) and juno (I. bucharica), Dutch, Spanish and English types, are among spring-flowering bulbs to plant now.
Natives of South Africa, freesias enjoy a warm, sunny position with a light soil. They give good results under cloches and in greenhouses, as well as in sunny parts of the garden.
Grape hyacinths, or matchheads, succeed almost everywhere, increase rapidly and can be naturalised under deciduous plants. There are white and double blue forms, as well as several species, the latter often difficult to obtain.
Bulbous irises flower over a long period, starting in late winter with the blues and purples of Iris reticulata. These irises like light, well-drained soil in full sunshine and will multiply surprisingly quickly if left to get on with it. Do not buy irises if there are black marks on the outside, as it indicates fungal disease.
Dutch, Spanish and English irises, which flower in that order, grow from 40cm to 70cm. Colours vary from deep purple to light blue, white, yellow and golden brown.
They all enjoy warm, sunny conditions and do best if the soil is kept moist but not waterlogged. They multiply quickly if planted in a suitable spot.
Lawn clippings are useful for mulching under shrubs such as rhododendrons, azaleas, roses and other surface-rooting plants at this time of the year.
Apply them only after the soil has been well watered and do not spread deeper than about 5cm.
Grapes will now be showing colour and some will be getting close to being fully ripe. An important task at this stage is to keep vines watered until the fruit is about half-ripe, giving liquid manure every week or two before watering. When grapes are half-coloured, give no more water until after the fruit has been picked.
Care must be taken to ensure grapes grown ingreenhouses have good ventilation, especially once fruit has formed.