Citrus care guide

For most of New Zealand, the backyard citrus tree is ubiquitous. Each winter they load themselves up on lemons, limes, oranges, or grapefruit; and we do our best to use them, or give them away.

While citrus are a relatively low-effort fruit tree, there are some common problems that many people bump up against.

Knowing what you’re doing can make a huge difference to the health of your tree.

Seasonal guide

There is a general rhythm to the seasons. At a high level, caring for your citrus looks like this.

Spring: begin fertilising (see fertilising tips below). If required, spray for insect or fungal issues (see spraying tips below).

Summer: continue fertilising and spraying. Mulch trees early in the season to reduce weeds and maintain moisture.

Autumn: Spraying may continue until the fruit begin developing colour. Pruning may begin. Harvesting begins.

Winter: Harvesting continues. Pruning may be done if required. Plants in areas receiving hard frosts or snow should be protected.

Fertilising

Commercial citrus fertilisers are usually blended to encourage maximum fruiting. They can come either as a liquid fertiliser, or a solid granular one.

If your citrus trees grow in pots, you should be using the liquid fertilisers every 2-4 weeks throughout spring and summer.

If your citrus trees grow in the ground, you can use a granular fertiliser once a month, or liquid fertilisers every 2-4 weeks.

Citrus-specific fertilisers are not generally considered organic. If that is important to you, you can use a more general fertiliser such as seaweed or fish emulsion. Try to find one with more Phosphorus (P) and Potassium (K) than Nitrogen (N) to encourage fruiting.

You can also fertilise with aged manure, or compost. Some people swear by the occasional wee on their lemon tree.

Epsom salts

Epsom salts are commonly recommended for plants with a magnesium deficiency. This usually looks like yellowing on your oldest leaves.

If you have spent a summer fertilising, mulching, and spraying your trees and the yellowness hasn’t lifted, then epsom salts might be the answer.

But most of the time, it’s not the problem. Magnesium deficiency can look like other problems, such as nitrogen deficiency, which can be addressed with a citrus fertiliser.

It’s worth trying to see if it’s another underlying problem before reaching for the Epsom salts.

Spraying

The best time to spray your citrus trees is in the evening as the sun is setting. A cloudy day will also work. Avoid spraying if you’re expecting rain as it can wash it off.

Never spray your plants during a bright, sunny day. Horticultural oil will heat up on the leaves of your plant in the same way oil heats in a frying pan. Even the water evaporating off quickly can be detrimental. Both can cook the leaves of your plant, leaving it damaged.

Use a sprayer with a wand and get under branches and behind leaves. Spray until the plant is dripping.

Doing this in the evening means that the spray has time to work overnight, and will evaporate with the dew in the morning.

Common pest – scale

A common problem on New Zealand citrus is scale – small sucking insects that leach the vitality from your plant.

They will look like raised dots, and may appear on bark, leaves, and fruit. Scale can be red, orange, brown, black, white, or grey.

A key giveaway that you have scale is you will see a lot of ants. They harvest the honeydew made by the scale. You may also see a black mouldy dust forming on leaves.

The answer to scale is to spray with a horticultural oil. There are several brands available. This is a mineral oil that by itself does not have any insecticidal properties.

Instead, the oil works to suffocate the scale. It covers their ability to breathe, and kills them via lack of oxygen. 

Common disease – verrucosis

Another common problem you might run into is Verrucosis. This is a fungal infection which causes scarring on the outside of the fruit, and makes branches grow spindly, with twisted leaves.

The answer for this problem is to spray with Copper Oxychoride. It’s more of a preventative spray than one that will fix the problem outright.

You may need to attack this problem over a long time-period, and you might need to prune out affected branches.

Copper Oxychloride comes as a blue powder and will leave a blue residue behind. It is safe to mix with horticultural oil and spray both at the same time.

But in the meantime, the good news is that the fruit is edible, if pretty ugly.

Pruning

Unlike pip or stone fruit, you do not need to prune citrus to encourage fruiting.

The main reason for pruning a citrus tree is because it’s in the way. Perhaps it’s growing into a path, or you can’t get the lawnmower underneath it.

Other reasons for pruning citrus trees include removing dead wood, and allowing for more airflow, which in turn helps prevent disease and makes spraying easier.

But the good news is, if it’s not in the way, you don’t need to prune it. And if you don’t prune it, lemon tree borer is less likely to be an issue.

Common pest – lemon tree borer

New Zealand has a native insect called the lemon tree borer (Oemona hirta). Young larvae bore into the stems of your citrus trees and kill them.

If you have a half-dead citrus tree, there’s a good chance this is your culprit.

Female lemon tree borers prefer to lay their eggs in cracks or freshly-pruned wounds in citrus trees, and are attracted to the scent when you prune.

There are two ways to prevent this. The most effective method is to prune in autumn and winter when the adults are no longer actively laying eggs.

Generally, breeding season is thought to be October to January, so it’s safest to do your pruning from March to September.

Additionally, sealing your cuts with a pruning paste will help prevent infestation.

Commercial pastes are available, or you can use my recipe to make your own.

Frost protection

Truthfully, this is not a problem I tend to have. Living in the Far North of New Zealand, we very rarely see any frost, let alone one hard enough to damage our plants.

But anyone living inland or down south will need to consider this before winter or a cold snap settles in. Some citrus trees are more tolerant of frost than others. A Meyer lemon grafted onto Trifoliata rootstock will have fewer issues with a frost than a Tahitian lime.

So if this might be an issue for you, get to know the frost tolerance of your citrus trees by doing a little research.

If your trees do need frost protection, there are a few options available to you. The most reliable is to physically cover your tree with frost cloth, an old sheet, or a specially-designed shelter. This will physically prevent the frost from forming on your trees.

Alternately, there is a spray you can apply which will help to protect your trees called ‘VaporGard‘.

This isn’t really my wheelhouse, but Julie-Ann over at Crafty Gardener has written great posts on using VaporGard (‘liquid frost cloth’), as well as using pre-made frost-cloth bags, and making her own frost-cloth bags.

Harvest and citrus recipes

If you look after your tree, it will be loaded with fruit that will need using as cooler temperatures set in.

If you live in a relatively mild climate, you can leave the fruit on the tree for a pretty long time. Our limes, for example, are usually still on the tree as we get to summer and really want them.

But it’s worth using as much as you can early to avoid it falling on the ground and rotting.

I’ve published a few of my favourite citrus recipes over the years. Feel free to use them!