Tips for Growing Healthy Citrus Trees
Citrus trees are evergreen trees suited to warm climates and can be adversely affected by frost. There are many varieties of citrus trees including oranges, limes, mandarins, blood oranges, native blood limes grapefruit and more.
They can be sourced on a range of rootstocks from large trees to as small as a stepover rootstock, almost a groundcover.
The fruit from citrus trees has been consumed since ancient times for food and medicinal purposes, and no wonder, they are a great source of Vitamin C, packed with fibre and are a rich source of flavonoids. Interestingly, a lot of the minerals are found in the skin of the fruit; so, keep eating the white pithy part of the fruit, it’s really good for you.
Citrus trees differ from other fruit trees in that they have roots very close to the top of the soil profile and do not have root hairs. This means roots can be adversely affected by a number of things, including raw or fresh hot manures, too much fertiliser, and soil temperatures.
Herbicide spraying close to the tree shade line can also have a negative impact on the tree due to the roots being poisoned, and soil fungi being damaged.
Citrus trees are heavy feeders due to the energy required to produce the abundance of flowers, chlorophyll for new leaf growth, and energy required for pollination and fruit set on the tree. They also need the presence of fungi in the soil to help uptake minerals.
This combination of factors often causes the tree to use up nutrients in the soil and become deficient, particularly in iron. Iron deficiency becomes most obvious when citrus tree leaves turn yellow from the outside leaf margins.
Citrus trees don’t like wet feet for prolonged periods of time. Sitting in clay or compacted soil without proper drainage will cause waterlogging; if the water can’t get away from the root system, the tree will struggle or die as oxygen and food are cut off from the tree. Healthy, well-drained soil is the key to growing strong healthy green and fruitful trees.
Sun can burn the skin of a citrus tree, so care should be taken when pruning in the hot months of the year. Take care not to remove any of the canopy that shades the trees branch understory. And be careful if your tree is growing in an area with a lot of reflective heat; for example, near a tin fence or surrounding concrete area.
When protecting your citrus tree from sunburn, spray Kaolin clay all over your tree from September through to December. This will protect your tree from sunburn while keeping the citrus leaf miner and gall wasp repelled at the same time.
Questions & Answers about Growing Healthy Citrus Trees
What is the right site?
Full sun position, soil enriched with compost and able to drain water off.
When is the best time to plant citrus trees?
The best time to plant in South Australia is September onward before the weather gets too hot.
This is when the soil is warming up and the tree is actively growing and can produce new roots quickly.
The last thing your citrus tree needs is to have its roots disturbed in the middle of winter, and then be waterlogged until the warm weather commences.
How do I fertilise my citrus tree?
This is a question I get asked often. My answer is to first feed with trace elements, then a different fertiliser every six weeks from September to April. Again, the “little and often” practice applies here. Don’t use too much fertiliser.
Always water the tree well before fertilising.
Typically, use GROlife, then cow manure, then Blood & Bone, then seaweed powder, then chicken manure. Small amounts: 1 cup around the shade line of the tree for a young tree; 2 cups for a larger tree.
Yellow leaves on a citrus tree can normally be a clear indicator of iron deficiency. When growing soils with a high PH and high calcium content, iron can be hard for the tree to absorb. This is the reason the application of iron should be applied above the tree and watered into the leaves, making its way through the window of the leaf—thereby bypassing the root system and picking up the iron deficiency.
Traditionally iron chelates were used to carry out the task. These days, Bass Laboratories produces a liquid iron that is much easier and a more efficient way to feed your trees.
As a general guide, observation of the leaves on your tree will identify deficiencies: yellowing from the outside of the leaf margins is generally iron, dappled yellow over leaf with green margin and vein is usually magnesium and manganese, and green leaf with yellow vein normally zinc deficiency.
Keep in mind some elements are only required in micro or macro quantities and overuse can cause toxicity in the tree. This is why one trace element feed per year is all that is normally required.
How do I keep the soil cool and the soil moisture stable?
Mulching around your tree is a great idea, but watch out for mulch against the trunk of the tree, as it can cause collar rot on your tree’s trunk.
If you want to protect your citrus trees always put a few bricks around the base of the trees to prevent mulch from touching the trunk. Alternatively, these days greenway plastic surrounds are also a very effective way to do the same thing.
Mulch will keep your soil cool in summer and keep soil temperature stable. This is an important factor in protecting the living organisms in your soil thereby maintaining the soil fertility.
What’s eating my citrus tree?
There are insect pests you will need to deal with and control, in order that your citrus trees stay healthy and viable.
The most common insect on your tree are most likely sucking insects like aphids or white flies. They are easy to see on the tree. They bore a hole into the leaf and suck out the chlorophyll. Because they are feeding on a rich source of plant sugar, their secretion is almost pure sugar. This presents a problem of attracting sugar-consuming insects and also sets up a perfect environment for black fungus to grow on the leaves and branches of your tree.
Citrus leaf miner is another common and obvious insect to detect. The leaf miner eats the leaf normally favouring the new soft, tender shoots at the top of the tree, leaving a chewed-off mark on the leaf similar to teeth marks.
Two-spotted mites are less common, but if detected, they would normally be found on the back of the leaf. They will cause the leaf to lose colour with brown spots appearing where colour has been drained out of the leaf.
These problems can be prevented by spraying eco-oil over the foliage of the tree from spring. Make sure the tree is well watered before you spray and avoid spraying on very hot days.
Gall wasp has become a major issue in the Adelaide suburbs in the last few years, so the protection of your trees should be a high priority from the beginning of spring.
See my blog entitled, Gall Wasp Treatment: Save Your Citrus Trees!
How do I grow dwarf citrus trees in pots?
Growing dwarf citrus trees in pots is more challenging than growing them in the ground. This is due to a few factors including pot temperature fluctuations and roots heating up. The trees develop a dry root ball underneath because water can only move in a vertical direction in a pot whereas, in the natural ground, water moves both horizontally and vertically, thereby wetting the tree underneath the root ball. Another issue is a build-up of salts in the soil that can’t disperse, especially from chemical fertilisers.
When planting citrus trees in pots, I only use 1/3 soil and 2/3 pine peat or potting soil medium. This will keep your soil friable and prevent compaction.
Watering should be carried out each time until it comes out of the bottom of the pot. This will help flush out salts in the soil.
Mulching the top of the pot will be essential in summer. Small pots are a bad idea as are black pots, which will scald the roots growing on the outside of the pot if they are watered in the middle of the day when the black pot is ‘red hot’.
Feeding the soil with humate-type products will populate the pot with microbial life essential for your tree.
Can I rejuvenate my old citrus tree?
People often ask me, “Why is my citrus fruit dry and tasteless?”
Of course, there are many reasons why this occurs, such as a lack of water, poor nutrition, bad soil, poor drainage, or the roots are too hot.
If the fruit was once very good but has gradually gone downhill, I recommend feeding and mulching using my fertilising regime to see how it goes.
If that doesn’t work, it’s time to rework the tree.
Skeletisation is a good option if the tree has a good healthy base. Check for rot or borer holes and if the base is healthy, it’s time to get pruning.
This should be undertaken in the cooler months of the year.
Prune every branch that is the thickness of the base of your thumb, ensuring your pruning gear is sharp and clean.
This pruning will expose the branches under the canopy to UV light. Covering them with water-based white paint, lime wash or Kaolin clay will protect them until the leaves grow back.
Why is my orange tree taking so long to grow?
Not all citrus trees share the same vigour. I have found oranges can take a while to grow whereas grapefruit and Lisbon lemons seem to thrive from day one.
Be patient and follow the disciplines outlined in this blog, and your tree will return fruit to you when it has matured and happily growing in your garden.
If your tree has a dark green colour and is producing new red growth on top, you’re doing a great job.
How do I prune my citrus tree?
On a normally healthy citrus tree, you won’t need to prune it much at all.
Remember, pruning the top will make the tree wider, pruning the bottom will make it taller, pruning the canopy will make the canopy thicker. All pruning will affect the tree in some way.
Prune off any old fruit, dead twigs, decaying or dying branches at any time, this will keep your tree healthy.
I tend to prune out Gall wasp as soon as I see them in a tree. I know some like to use the potato peeler. My response, particularly on a young tree, is to remove and prevent further attack.
Avoid pruning the single shoot that springs up out of the canopy and causes the tree to look lopsided. It will soon balance itself out without any intervention.
Remember, pruning stimulates growth and unnecessary pruning will cause too much growth. This will make the canopy too dense and hard for light to penetrate it. When this occurs, fruit will normally only grow on the outer sides or peripheral outsides of the tree.
Skirting or pruning the lower branches close to the ground is good practice. This will prevent limbs from contacting the ground, removing a pathway for mould or insects to infect your tree. It also helps with maintenance under the tree, picking up fallen fruit, fertilising and mulching.
It is also good practice to pick all the old fruit off the tree at the end of the season, including any fallen fruit. This will reduce the incidence of disease and insect attack on your tree.
I hope that answers most of your questions about growing beautiful citrus tress. If you’re still unsure, give me a call.