How to deal with common winter citrus plant problems
Picking ripe citrus fruit brightens up a winter day. The peak harvest season for lemons, limes, grapefruit, tangelos and mandarins runs from June to September. Backyard trees should be laden with fruit now but wintry conditions can be a challenge for these subtropical trees. Here's how to look after your trees and save your crop.
Five common problems citrus have in winter
1. Scabby marks on the skin
Verrucosis or citrus scab can affect all citrus fruit. It looks unsightly but the quality of the fruit inside is not affected. If you want picture perfect lemons or lots of zest for cooking, you can spray with copper. If you're just after the juice you can let it be.
2. Brown scaly patches at the end of the fruit (not the stem end) and early fruit drop. The fruit is also often dry
This is blossom-end rot. It's due to lack of calcium- either because it's lacking in the soil or there has been drought or irregular watering so the tree couldn't take up enough nutrients to support the growth of the fruit. It is a sign of malnutrition rather than disease and is easily treated - although there's nothing to be done for fruit already afflicted. The addition of lime (a handful or two per tree) around the drip line would be an effective stand-alone remedy, but you might as well cover all bases by applying citrus food too. Citrus are among the greediest plants and are always starving for one thing or another.
3. Frost damage to citrus foliage
There's nothing you can do once the damage is done - and indeed doing nothing is the best course of action. Never prune off the frost-damaged stems and foliage of citrus trees. Pruning now only encourages them to produce soft new growth, which frost will attach again without mercy and that second strike often proves fatal.
Keep a roll of frost cloth handy to drape over trees when frost threatens. Make a framework of stakes around the tree so there is a gap between the cloth and the leaves of the tree. Or spray citrus trees with Liquid Frost Cloth every six weeks instead.
4. Lack of fruit
Citrus trees are subtropical plants but some can tolerate cooler conditions than others. 'Meyer' lemons are the most reliable variety for colder areas. We have heard recently from a reader who had a 'Meyer' lemon and a mandarin side-by-side in her Christchurch garden and the lemon was covered in fruit while there was never any fruit on the mandarin - truth is, her garden was probably too cold for it. It doesn't mean you can't grow citrus, remember it can also be grown in pots, tunnel houses or glasshouses where they thrive in the warmer conditions.
5. Yellow leaves
Kate Marshall from Waimea Nurseries says citrus foliage can sometimes turn to yellow tones in winter. If the leaves are entirely yellow, this is usually just a natural process for the tree – most citrus trees are grafted onto Trifoliata or Flying Dragon rootstocks, which are deciduous on their own. Therefore, when used as a rootstock in winter the roots stop taking up nutrition, leaving the evergreen part of the tree hungry for food. Margined or mottled yellow leaves are a symptom of nutrient deficiency.
Kate recommends waiting until spring to feed with general citrus fertiliser, as the deciduous rootstocks won't take up any food during the winter months. Fertilising citrus in the cooler months can be tricky, as it is best to avoid encouraging a flush of tender new growth that could easily get frosted or cold damaged. Instead feed with Dolomite lime and gypsum, which will increase trace element nutrition and improve leaf appearance without stimulating a flush.
How do you look after your citrus trees in winter? Share you tips with us in the comment section below.
Written by Barbara Smith. First appeared on Stuff.co.nz.
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