Last updated on January 21st, 2020
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Citrus plants are not a hardy British plant, but you can still grow them successfully if you plant them in pots outdoors for summer, and bring them indoors for winter.
The most common citrus tree to grow in the Uk, especially in milder parts of the country is the Meyer lemon but equally tolerant of cooler temperatures are kumquats but they all still need to brought indoors over winter as there only hardy to around 10 degrees Celsius, slightly lower for Kumquats.
If you grow limes or lemons you will need to provide a bit more warmth in a slightly warmer position when brought indoors over winter. What we like about all of these citrus trees is that the fragrant flowers will appear throughout the year but they will be particularly abundant near the end of winter. The fruit starts to ripen between 6 and 12 months later and eventually you’ll have flowers and fruit at the same time.
Growing citrus trees in the Uk
Place citrus trees outdoors in summer and bring inside over winter
Citrus trees need to be grown indoors during the cold winter and then put back outside for the rest of the season over summer once the weather improves. They do quite well outdoors during the summer as long as they have a sheltered, sunny area with access to around 6 hours of direct sunlight.
Protect with fleece in early summer in case of a late cold snap
It’s important that you keep some horticultural fleece on hand to help offset the sudden cold snaps that can manifest at the beginning of Summer as we have been known to have a late frost that can damage the flowers.
Between June and September, the temperature should be good enough but on the off chance that something unexpected happens, it’s better to be safe than sorry. Lower temperatures can inhibit flowering and when that happens not only do you not get the citrus fruit that you wanted but it can permanently damage or on rare occasions, even kill the plant entirely.
Minimum night time temperatures
Minimum temperatures at night for limes and lemons need to hover around 10 degrees Celsius minimum. Oranges need minimum temperatures around 13 degrees Celsius so need to be slightly warmer. Kumquats are different in that you eat the entire fruits as well as the skin and they can tolerate winter temperatures down to 7 degrees Celsius so are slightly hardier. In fact, kumquats are some of the strongest in terms of cold tolerance out of all the citrus trees you can grow so are sometimes better suited if you have a cooler room over winter.
Repotting citrus trees
No matter the type of citrus you choose to cultivate you should repot them every few years when they get too big for their container and this is something that needs to be done at the beginning of Spring. Alternatively, you can replace the top 5cm of potting soil with fresh compost on an annual basis is the pot is already quite sizable, this should also be done around March. We recommend using a specialist citrus compost or use John Innes Number 2 compost mixed with around 25% horticultural grit or coarse sand.
Food and Water
Feeding citrus trees
When you grow citrus trees in containers they are, depending on the type, very hungry plants. You’ll need to provide a high-nitrogen citrus summer food starting at the end of March all the way through October and then make a switch to a winter citrus feed. Many lemon trees need fertilizer every month during spring and summer and then once a quarter during autumn and winter with additional feedings whenever you transplant them into a new container in March.
Watering citrus trees
They should be watered regularly throughout the summer, twice a week if they are in an indoor container and every other day if they are in an outdoor container. This should be adjusted based on the weather. As winter approaches you should allow the surface of the soil to partially dry out before you water them again. Over-watering in the winter is among one of the most common problems that container-grown citrus trees have.
If you bring your containers indoors for the winter it’s important that you maintain a high level of humidity. Citrus trees thrive best in areas that have 50% humidity, something you can measure ahead of time before deciding on the final resting space for your indoor pots. You can place the pot on a large saucer filled with gravel and then hand missed the citrus trees regularly with a sprayer to help maintain high humidity when you move them indoors.
Pruning and Training
citrus trees require very minimal pruning and realistically should only be pruned to control growth early on to encourage more lateral branches for the sake of training a young tree. You can reshape your plant by sitting out any overcrowded branches in February. If your tree is particularly leggy you can prune it back, by up to 2/3, cutting back the tallest branch to encourage that lateral growth. Throughout the summer you can regularly nip off the tips of the most vigorous growth to help encourage better flowering and subsequently better fruit.
Dealing with water shoots
Pay particular attention for water shoots, The Unwanted shoots that grow below the graft on your main stem. If you see any of these you should remove them immediately.
Where to Put the Pots
Place where they will get at least 6 hours of sun per day
When choosing a location to put your pots outdoors remember that they need a very sunny area. Citrus plants need access to at least six hours of direct sunlight every day whether they are placed indoors or outdoors. Most citrus trees will reach between 1m and 1.5m in height and they grow better in warmer climates with access to direct sun. During the summer they do run the risk of root burn but only if they receive more than 12 hours of sun every day so this is not usually a problem in most parts of the UK.
Make sure that you plant a new tree in the spring, the same time that you would transplant more mature trees and if you’re going to move them outside earlier than the middle of June, keep that horticultural fleece on hand in case the temperature drop below whatever minimum your particular citrus tree can handle.
The most common problems your plant will face indoors is mildew and problems associated with too much water. Outdoors though, they are at risk from mealybug, scale insects, and spider mites. All of these are quite small and unless you regularly examine your plant for them, you might very well miss them until such time as they have taken over.
Spider mites, for example, are often discovered one the leaves are mottled, pale, covered with webs. Similarly, mealybugs are often noticed once they have started sucking out sap and leaving honeydew in its place, the result of which is black, sooty mould on your leaves. All of these problems are best dealt with in a preventative fashion, regularly maintaining the soil, air circulation, and water conditions at the appropriate levels. If you do see an infestation it’s imperative that you use commercial products to get rid of them immediately so that they don’t spread but be sure to use a pesticide that is safe on fruit.
Harvesting citrus fruits
Citrus trees are self-pollinating so you only need one to get fruit. If you have a plant that is up to one meter tall it shouldn’t produce more than 20 individual fruits. Limes, lemons, and oranges and grapefruits might need thinning here and there but kumquats don’t have to be thinned at all.