How to protect them from frost
Winter is coming but the cold has its advantages too, explains Kate Marshall.
Bugs such as guava moth and thrips detest the cool and after a decent cold snap seem less problematic the following summer.
We don’t always welcome winter with open arms, but cold weather has an important role in the orchard. While it’s important to keep fruit trees covered during cooler months to prevent damage, pesky bugs hate the cold too. And of course deciduous fruit trees actually require a certain level of winter chilling to be productive.
Deciduous fruit trees need varying amounts of cold weather, with ‘high chill’ varieties such as apricots ‘Moorpark’ and ‘Sundrop’ loving the cold snaps. In contrast, ‘low chill’ varieties, such as apricot ‘Katy Cot’ and cherry ‘Lapins’, only need around 500 hours under 7°C, which is even achieved in the winterless north. In a mild winter, varieties with high-chill requirements will only produce a smaller crop – so that makes for a good reason to celebrate frosty July mornings and looking ahead to bumper summer crops.
The cold weather also helps to disrupt the life cycle of pests and diseases. Bugs such as guava moth and thrips detest the cool and after a decent cold snap seem to be less problematic in the following summer season.
Autumn: be aware
Autumn is a tricky time of year. Keep plants protected from unseasonably early frosts, which can damage the last of the summer’s tender new growth. Use a swathe of frost cloth fabric to cover trees, or apply liquid frost cloth or Vaporgard.
The last of the autumn crops, such as feijoas and figs, will stop ripening after a frost or two. To get the best out of them, plant these laterripening fruits in the warmest part of the garden, or plant them in pots so you can move them into the heat or shelter as the weather cools.
Winter: cover up
In winter, deciduous trees are in full dormancy so there is no risk of damage. However, subtropical and tropical fruits, such as passionfruit, pineapples, citrus, avocados and bananas, will need some cover from temperatures going below zero.
Spring: remain vigilant
Tender petals are sensitive to cold stress and frost damage, so spring is a risky time for deciduous fruit trees coming into flower. Fling frost cloth over trees overnight and remove it in the morning to open up the blooms to pollinating insects for the day. Or use the irrigation method employed by professionals.
Cold temperatures, rain and wind are not ideal conditions for pollinating insects, so if it’s practical – for example with smaller trees – use a paint brush to manually move pollen between flowers. Move the pollen on the same tree if it is self-fertile, or between trees if you are cross pollinating partners.
Use frost cloth
The sun warms the ground during the day and that heat is trapped under the frost cloth to protect young trees during cold periods. Put the frost cloth on just before the sun sets, to trap the heat the ground has stored during the day. The frost cloth should touch the ground at the drip line of the tree, and can be pinned or weighed down to seal the warm air in. The tree should be entirely covered, but the cloth should not touch the leaves (as frost will transfer through the cloth directly onto the leaves).
Try liquid frost cloth
There are several similar pine oil-based anti-transpirant products available, including liquid frost cloth and Vaporgard. These protect the plant by stopping the leaf cells from collapsing. Spray products onto the tree when the first frosts start, and then again about eight weeks later – that should give coverage for the whole winter.
DIY irrigation
Irrigation is a technique used by commercial orchardists involving aiming a sprinkler over trees for the night, creating a frozen protectant layer for buds and blossoms. It seems counterintuitive but this creates conditions for a more gentle, gradual freeze and defrost, rather than a short, sharp temperature dip around dawn.
Move it
For fruit plants in pots, don’t forget to move the tree into a warmer or protected spot. Plan ahead when potting your fruit trees, and put castor wheels on the bottom of the pots. Good spots to move pots to include under the eaves of the house or into a conservatory.