How to Raise Healthy Citrus Trees
By T. Jeff Williams
There’s something special about a citrus tree in your yard. You may have other trees that are taller or more colorful, but none speak to health and happiness like a citrus tree. Some bloom practically year round, and the scent of orange blossoms in the evening air is a memorable perfume.
Think of the variety available to anyone who wants to grow citrus: grapefruits, oranges, tangelos, mandarins, lemons, limes, tangerines, kumquats and limequats. There are nearly 100 varieties of oranges alone. Lemons and limes do wonders to enhance the flavors of food and drinks.
Citrus plants do well both indoors and outdoors and with some proper management you might have year-round citrus crops. They don’t always have to be a tree, either. Lemons make excellent hedges, as do dwarf navel oranges.
Citrus plants do best in subtropical climates, which exist in much of California. The state is subdivided into three major growing climates: the cooler coast, warm central valley and the hot dry desert.
A key factor in the sweetness of citrus fruit is heat. The hotter the growing season, the sweeter the citrus, which is why the best grapefruit comes from desert regions in California and Arizona, and certain areas of Texas.
When considering planting citrus in your yard, consider the microclimates that exist there. For instance, the south side of the yard will be the warmest section, which might be the best spot if you plan to grow grapefruit. Citrus do better if sheltered from wind, so espaliering them along protective fences is one solution in windy areas.
In frost zones, draping a blanket over a tree small enough provides good protection. For larger trees that you value construct a portable framework to surround the tree during frost season. Don’t just cover a citrus bush or tree with plastic sheeting because frost can burn through plastic where it touches the leaves.
Citrus trees are hardy enough to survive in anything from clay soil to sand, but obviously are going to do much better in well-drained loamy soil. If you have clay or sandy soil, you will be much happier down the line if you spend time prior to planting to create ideal soil conditions. Mix large amounts of mulch and good topsoil into your garden earth over a large area, larger than you might imagine, down at least three feet. A 15-foot tall orange tree, for instance, may have roots that spread 15 or more feet out from the trunk. If the soil is particularly heavy clay, you can also build a large raised bed.
Choosing a tree
When buying a tree at a nursery, look for trees with smooth, clean bark and bright green leaves. The graft union, where the scion (new cutting) is grafted to the rootstock, should be smooth. For a dwarf citrus, the graft union should be about five inches above the soil level and 10 to 12 inches above the soil level for full-sized trees. Dwarf citrus should have branches about 5 to 10 inches above the union, while standard citrus should branch out 24- to 30-inches above the graft.
Check the roots if possible and avoid trees that have extensive and matted roots inside a pot. This indicates the tree has been too long in the pot. Check bare root trees carefully for broken roots. And avoid choosing a young citrus for transplanting that is already bearing fruit. A tree mature enough to bear fruit may have been too long in a container.
How to plant
Spring is best time to plant a citrus tree. This gives the tree all spring, summer and early fall to become acclimated to new soil and climate.
Dig a hole the depth of the rootball and twice its diameter. Remove the tree gently from the container and set in the hole. It’s important that the top of the rootball be flush with the ground. Do not pile soil around the base of the trunk, which can lead to various diseases.
If planting a bare root citrus, make a mound at the bottom center of the hole and gently fit the roots around and over the mound. Make sure the mound is firmly packed so the tree does not settle below the soil line.
After backfilling and firmly pressing the soil around the root ball, build a small berm around the plant and water thoroughly.
Proper attention to watering is most important with young trees, which are more subject to stress from drying roots. Keep the ground moist for the first six months while the roots are establishing themselves.
A good rule of thumb in watering these trees is to dig a small hole near the drip line six inches deep. When the soil at the bottom of the hole is barely damp then water deeply, to three or four feet. One way to tell that water is penetrating fully is to push a thin metal rod down into the soil. If the soil is well watered, you should be able to push the rod down three feet.
As the tree matures, water less frequently but deeply each time so water penetrates below the root level. Watch for any signs of tree wilt during hot days. A combination of heat and wind will dry out soil rapidly and more than one watering a week may be required, particularly with young trees.
Keep water away from the trunk by building a dirt wall around it about a foot away. A continually wet trunk can lead to collar rot, which is often fatal to citrus trees. A thick layer of mulch around the base of the tree keeps the ground from drying out too soon and helps control soil temperatures. Again, keep wet mulch away from the trunk.
Citrus trees need a steady supply of nutrients from spring through early fall, and nitrogen is their biggest need. Many growers simply apply ammonium sulfates directly on the ground around the trees. This fertilizer contains both nitrogen and sulfates, essential for good growth.
A better choice is the complete fertilizer found in the Citrus and Avocado Food boxes available in all OSH garden centers. These fertilizers also contain the basic elements of nitrogen (N), phosphorous (P) and potassium (K), plus important trace elements of magnesium, calcium sulfur, manganese and iron.
Fertilize your citrus tree by spreading the pellets evenly over the ground around a tree from the trunk to the drip line, or the outer edges of the branches. Use a shovel to work the fertilizer lightly into the ground and then water thoroughly, allowing the water to dissolve the fertilizer and carry it down to the roots.
For amounts to use, follow the manufacturer’s recommendations on the fertilizer bag. Do not fertilize newly planted citrus trees for the first year or you risk burning the roots. Using the recommended amounts, fertilize established trees in February and at regular intervals through the summer. Do not fertilize after late August or early September because you do not want to encourage fast young growth as winter and possible frosts arrive.
Citrus trees as a whole need little or only moderate pruning. But because the appearance of a tree is important, the tree may need some pruning to maintain a balanced and even growth pattern.
Citrus trees can be pruned any time of the year, but it’s better to prune prior to blossoming.
Cut away dead and diseased limbs as you see them. Remove all suckers growing up from the base. Orange trees should have limbs and foliage reaching nearly to the ground, which helps protect the trunk from sunburn.
Lemon trees in particular often have limbs that grow too rapidly into awkward angles. Some light pruning to keep the wayward branches in check while other limbs around the tree catch up is often in order. Keeping lemon trees balanced by pruning rapidly growing branches may slightly reduce the crop but will give the tree an attractive shape.
Common Citrus Problems:
- Sunburn: Citrus bark is thin and easily damaged by extensive exposure to summer sun. Until the tree has matured enough to provide sufficient shade, protect the trunk by wrapping it with burlap or painting it with white latex paint thinned 50 percent with water.
- Holes in the leaves: Snails love citrus trees and may remain in a tree for weeks as they munch through the leaves. Look for snails in the evening and hand pick. A copper wire or band around the base of the trunk will keep them from climbing into the tree.
- Fruit and blossom drop: Citrus trees put out far more blossoms than can be turned to fruit. As a result, the trees are programmed to spontaneously shed blossoms and young fruit as a means of protecting themselves. How much of a drop depends on temperatures and water, but it is a naturally occurring phase. Also, be aware that some citrus trees bear heavily one year and little or no fruit the next year so a lack of crop is not a cause for alarm.
- Fruit splitting: Sharp weather changes involving high humidity followed by a hot dry spell can cause fruit on the tree to split. Only a few fruit on the tree are usually affected.
- Gummosis or foot rot: This often occurs in winter when wet soil or water stands for extended periods against the base of the tree. It is more prevalent in area with clay soil that does not drain well. Symptoms include dead or decayed patches of bark below the graft union. Significant amounts of gummy sap may also be seen in the area. To counter the disease, peel away infected bark and spray with a copper-based fungicide.
- Gumming: A citrus tree will attempt to cure damage to its trunk by oozing sap from the break in the bark, much like cut skin forms a scab. If you see such damage, often caused by a lawn mower or other hard object hitting the tree, recognize that it is a natural defense and not gummosis.
T. Jeff Williams is veteran builder, landscaper, gardener and former rancher who brings years of practical experience and a journalist’s background to his subjects. He has authored and co-authored some 15 books on these subjects, including books for Sunset, This Old House, Better Homes and Gardens and Ortho Books.