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The roses have just completed their October marathon and it is time to power them up for the next show in December.
Monthly fertilising, from September to April helps them flower for 10 months of the year and grow strongly, which makes them more heat and drought tolerant. It is easy to spot hungry roses; the leaves are light green, the bushes don’t grow or flower well and are easily affected by black spot, even after spraying.
The simplest way to give roses the food they need is to follow the recommended dose, worked out by fertiliser manufacturers who have based it on the nutritional requirements of the rose. Giving double the amount of fertiliser won’t make a rose grow faster. It will more likely burn its leaves and may even kill the rose.
For instance, Vigorosa 5:1:5 (25) contains the right mix of nitrogen, phosphorus, and potassium as well as Epsom salts, lime and micro elements for flowering, root and shoot development. It also contains humic acids, which play an important role in improving the soil structure and water retention capacity.
The recommended dosage is 30g per rose bush, 15g for miniatures or newly established roses and 60g for large climbers. Each Vigorosa bucket contains a 30g measuring cup. For best results feed every four to six weeks, depending on how hungry your plants are.
Many gardeners give Epsom salts but that only supplies a single micro-element and there is the danger of overdosing. However, if the soil tends to be too alkaline, watering with Epsom salts will acidify it. Gardeners also wonder about the effectiveness of foliar feeds, but a rose feeds best through its “feet” so one should never replace a granular fertiliser like Vigorosa with a foliar feed.
However, soluble Phostrogen rose food and tonic can be added every two weeks. It is in a chelate form, which means it is immediately absorbed and available to the leaves and stems. The calcium and potash strengthen the cells, making blooms better and longer lasting. Chlorosis, which is indicated by yellowish leaves and pronounced green veins, is caused by the roots being unable to draw iron out of the soil. Soil compaction and poor aeration is usually the cause of it.
A sprinkling of 50g of LAN around each bush may help, as may digging in coarse compost. There are some simple dos and don’ts when applying fertiliser. Do not place heaps of fertiliser around the base of the rose, especially standard roses.
This is too concentrated and could burn the leaves. The best way to apply fertiliser is to sprinkle it over or around the bush, to fall on top of mulch. Shake or wash off any powder that did not roll off leaves.
Fertiliser granules that stick to wet leaves will burn them. If there has been rain, wait until the leaves dry out before fertilising.
After fertilising, water deeply so it goes down to the roots. Not watering enough could result in fertiliser burn, which is quite easy to recognise. In severe cases the stems become black with brittle black-brown leaves. Do not fertilise roses that have lost their leaves. Without leaves the fertiliser cannot be converted by the process of photosynthesis. Wait until new growth appears on the upper parts of a denuded bush. Then break out the tips of the new red shoots. This will force the bush to start sprouting on the bare lower part. Once new shoots have sprouted a small dose of fertiliser can be
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