CAN YOU OVER-WINTER CITRUS OUTSIDE?
This is an excellent question to which the answer is obvious – it’s yes and no! There is of course a serious point behind this ambiguity which is due of the number of variables involved. Successful over-wintering of citrus will depend on the variety, where it is planted, how you have prepared the surrounding area and what protection - if any - you are going to provide. Below is a breakdown of these factors and the explanations behind them.
COLD HARDY CITRUS VARIETIES
The first and perhaps most important consideration is the selection of a quality cold hardy citrus variety. Even though citrus evolved originally from the tropics they do possess a natural ability to withstand reasonably cold temperature when given the chance to harden off. Kumquats and satsumas are the most cold-hardy of the edible forms of citrus available while is the most cold-hardy of all citrus. The trifoliate orange also makes an excellent rootstock as it will pass on its hardiness to the scion variety budded onto it. Therefore, kumquat and satsumas budded onto trifoliate orange rootstock are the hardiest of all grafted varieties.
HOW COLD IS TOO COLD?
The duration of freezing temperatures can be a more critical factor than the actual minimum temperature. For example, serious damage may not occur during a brief drop to -5°Celcius, but damage can result after several hours at -3°Celcius. Moreover, previous exposure to cold weather will increase the plant's ability to withstand even colder temperatures. As the days shorten and nights get cooler, plant metabolisms will naturally begin to slow reducing active growth and improving cold-hardiness. Satsuma plants may be able to withstand temperatures as low as -9°Celcius in January when they are completely dormant and hardy, but they can be seriously damaged during a -3°Celcius cold snap in November.
WHERE SHOULD YOU PLANT CITRUS
Cold air wafts downhill, so planting citrus on the higher ground will be - to some extent - warmer than a position at the bottom of a slope which can also carry the risk of being a frost pocket. Planting on the south side of your garden is important as this will allow the plant and surrounding soil to make the most of the ambient heat and sunlight. The positioning and distance that your citrus plant is from the house can also be a crucial factor and is often overlooked. Plant your citrus as near as you can to the south side of your house but without leaving it in the shade. Most cold weather will come down from the north and northwest so you will be using your house as a windbreak, forcing the cold air up and over your citrus trees and leaving the area near the south side somewhat warmer. The house itself will also radiate a certain amount of heat, some of which will be absorbed by your adjacent citrus plants. Overhanging trees can also maintain a slightly higher air temperature within their canopy and will also reduce the incidence of ground frost. Although this does give a clear over-wintering temperature advantage, growing citrus plants beneath other trees is not a fantastic option as their summer shade will result in poorer growth and lower fruit yields.
The ground below and around a citrus tree should be completely free of weeds, grass, mulch or anything else for that matter during the winter period as these will all act as an insulator barrier. This will prevent solar heat from entering the soil during the day which will mean that there is less heat stored for release from the soil at night.
Moist soils will absorb more heat than dry soils, so trees should be carefully watered 2-3 days before a bad frost or freeze is predicted. Water too much though and you will risk water-logging the root environment which can cause root death so make sure that before you plant your citrus you have provided a free-draining soil!
Good tree health and nutrition is also important when it comes to helping citrus trees withstand freezing temperatures so make sure that you follow a good maintenance regime during the growing season. Fertilization and pruning should come to an end in August or September as this will allow the trees to harden off completely before severe frosts are encountered.
Young citrus trees should be ‘banked’ for the first 3-5 winters until they are mature enough to withstand the colder temperatures. Banking is a technique where the surrounding soil is pulled up into a mound around the tree to cover the bud union and lower trunk. Even if the exposed parts of the tree are completely killed off through cold damage, the bud union under the bank should still survive to grow back in the spring.
Citrus trees may be covered temporarily with blankets, quilts, paper or other material as a protective barrier against hard frosts or snow. Remember to remove all covering protection in the morning to allow citrus trees to take full advantage of the warmth and light – however weak – from the available sun.
For more information click onto:
Cold Hardy Citrus Varieties for Over-Wintering Outside
How to Grow Citrus from Seed
How to Grow a Lemon Tree from Seed
How to Grow Melons in a Greenhouse
How to Grow Melon Plants from Seed Outdoors
How to Grow an Orange Tree from Seed
How to Over-Winter Citrus Plants outside
How to Over-Winter Lily Bulbs
How to Protect Tree Ferns Over Winter