GROWING CITRUS TREES

A citrus fruit is a tart, edible fruit produced by a citrus bearing tree (Citrus species). Citrus trees are grown in the Middle East as well as tropical and sub-tropical environments with warm winters and long growing seasons. Citrus have been cultivated by humans for thousands of years. There are several species and named varieties of Citrus, so it is important to choose one that is right for your area and taste preferences.

CHOOSING A VARIETY

SIZE

Our citrus trees are grafted on to dwarfing rootstocks, and can be maintained at 3-10‘tall and wide, depending on variety and whether they are grown in the ground or in a pot.

POLLINATION

Citrus are self-fertile, so do not require a different variety as a pollenizer to produce fruit.

RIPENING TIME

Fruit ripen late fall to early winter depending on your location and variety. Meyer Lemon, if kept above 50°F, will produce multiple flushes of fruit throughout the year.

USDA HARDINESS ZONE

Citrus are hardy to USDA zones 9-11. This rating tells you the minimum winter temperature the plants typically survive when properly hardened off. On our web site you will find a USDA Hardiness Maps which provides information on the average minimum winter temperature in your location, by zip code.

CHILL HOURS

Many plants native to locations that have cold winters have a Chill Hour requirement to ensure uniform waking up of flower and leaf buds in the spring. The chill hour requirement of plants varies by species, by cultivar, and sometimes by the level of dormancy achieved.

WHERE TO PLANT YOUR TREE

Citrus need to be planted where they receive at least 8 hours of direct sunlight measured in early summer (late June to early August). Sufficient sun exposure triggers the initiation of new flower buds for the next growing season, without which there will be no fruit. Fruit ripening and flavor development are also benefited by the carbohydrate production stimulated by the sun, as well as it’s heat.

Citrus prefer a sandy well drained soil that is moderately rich with a pH around 5.5-6.5. Improve your soil where you intend to plant by mixing an inch or two of plant based organic matter (manures are best for vegetable gardens), peat, or coconut coir into an area 1 1/2 to 2 times the diameter of the needed planting hole and up to a foot deep. A 2-4” deep layer of mulch (straw, leaves, or wood chips) applied after planting will continue to improve the soil.

Allow sufficient space for both the top of the tree and it’s roots when selecting the planting location. Refer to size descriptions for each variety, keeping in mind these are generally managed or pruned sizes, not maximum potential sizes. If you are planting an orchard be sure to include enough space between rows for transporting supplies in and fruit out.

GROWING IN CONTAINERS

In many parts of North America many forms of citrus cannot be cultivated outdoors without a greenhouse so many homeowners choose to keep their citrus in pots that can be taken indoors. Most citrus cannot survive temperatures below 25 degrees Fahrenheit.

To grow a Citrus tree in a pot you need a final container size of at least 10-20 gallons. Trees will grow larger in a larger container, but make sure you have the ability and tools to move the pots heavy weight. It is important for the establishment of the root system to gradually increase the size of the container over several years, rather than go from small directly to very large.

Do not use soil from your garden in the pot, instead use an acidic potting soil mix with some added sand For larger pots use a potting mix that has larger particles in addition to the smaller.

Citrus plants are also sensitive to drafts and sudden changes of environment (temperature, humidity, or sun intensity) which can cause them to lose their leaves. When moving indoors or out make the change gradually. If growing indoors, set the pot in a sunny window so it gets bright sunlight, or use grow lights. In an indoor environment citrus (and most plants) can rapidly develop severe insect infestations due to the absence of the natural predators that would otherwise keep these pests under control.

Citrus need lots of oxygen in the root zone, allow the soil to get quite dry between watering. Let the container dry until the soil is dry to the touch 3-4 inches down (more deep with deeper pots) and the container is lighter in weight. Add water until it comes out the bottom of the pot to ensure you fully saturate the container, then allow to dry again. Shoot tips and stems turning a wet brown color indicate the soil is staying too wet.

CARE AND MAINTENANCE

WATERING YOUR TREE

This is the most important and often the most difficult part of successfully growing plants. There are many factors, including the humidity, temperature, soil type, wind, and amount of direct sun that affect how much and how often water should be applied.

A general rule of thumb for plants in the ground is to ensure they receive an inch of water per week over the root zone. An inch of water is equivalent to about ¾ to one gallon per square foot of soil surface area. The typical three foot diameter planting hole would need 7 ½ to 10 gallons of water per week provided by rainfall or by the gardener.

Apply this water once a week, two times per week if soil is fast draining. This will of course depend on your own conditions and the plants you are growing! DO NOT waterlightly each day because this results in a wet surface and dry root zone area. The soil should be moist but not soggy to a depth of about a foot for most growing plants. The top inch or two can feel dry, and the plant still be well watered. The trick is to have the water available where the roots are. In hotter and sunnier areas, a mulch of straw, bark, etc. can greatly ease the burden of summer watering. For plants in containers, water until the soil is saturated and water comes out of the drainage holes. Citrus need lots of oxygen in the root zone, allow the soil to get quite dry between waterings. Let the container dry until the soil is dry to the touch 3-4 inches down (more deep with deeper pots) and the container is lighter in weight. A plant that has wilted canbe receiving either too much or too little water.

In rainy areas like the Pacific Northwest most of the plants that we offer will need relatively little supplemental irrigation ONCE THEY ARE WELL ESTABLISHED in the ground and have had a chance to develop a good root system. However even here it is important to make sure plants have regular, deep watering during the first couple of growing seasons, and the first summer is especially critical. In drier areas, or where soils do not retain water well, permanent irrigation is essential. Remember that you don’t want your trees to just survive, but rather to thrive. Make sure they get the water where they need it, starting at the drip line and extending away from the tree up to several feet ( for older trees) where the feeder roots will be. Drip irrigation and soaker hoses can be an efficient way to deliver the water.

FERTILIZATION

For good steady growth and high productivity, your trees need to have adequate amounts of various mineral nutrients. Some people are fortunate and have naturally rich fertile soil. Many soils, however, are deficient in some nutrient or another and use of fertilizers, organic or chemical, can be highly beneficial if you want your trees to grow well. If you have a large garden or orchard it can be well worth it to have your soil analyzed by a qualified laboratory so you know for sure just what your soil needs. Typically this might cost $30-$60, depending on how detailed an analysis you want. Unless you know what is available in your soil, you will not be able to supplement it properly.

Use a fertilizer designed to meet the needs of citrus trees. A couple of inches of well-rotted compost on the root zone can also be an effective fertilizer. A generous leaf wood chip mulch around your trees will not only conserve moisture and help in weed control, but also keeps your soil healthy by building up humus, attracting earthworms, and supporting beneficial fungal organisms. This encourages young trees to be strong, healthy and productive. Use of concentrated products like chemical fertilizers or strong organics (for instance blood meal) is usually done from late winter through early summer. Applying fertilizer after early summer can encourage lots of soft new growth that is much more likely to be damaged by winter cold. Excessive use of fertilizer can in-crease disease problems on your plants and can even kill them. Use of too much fertilizer, whether chemical or organic, can contribute to stream and groundwater pollution, so please try not to use more than your trees really need. As a general guide, if your tree is producing about one foot of new growth or more a year and has healthy looking foliage, it may not need much or any fertilizer.

PESTS AND DISEASES

Find out what insects and diseases are typical in your area. Ask your local co-operative extension professional what the typical insect and disease issues are in your area. Then you can make selections based on resistance or tolerance information available in our catalog, or, make a plan for controlling problems you can expect with the susceptible varieties you prefer to grow. If you see resistance information about a particular disease for one variety but not another of the same kind of fruit, then that variety may be susceptible or might not have been tested so is unknown. The following are some of the more common issues.

ROOT ROT

SYMPTOMS - Terminal leaves of shoots turn yellow or brown, then drop. Shoot tips turn brown, may curl. Entire plant wilts easily or looks dull in spite of regular watering.

CONTROL METHODS - Allow soil in container to dry between thorough waterings. Provide bottom heat to hasten drying until roots are established in the pot.

COMMENTS - Prevent by using a container just a few inches wider than the roots. Caused by lack of oxygen in the root zone displaced by excess water. Use coarse potting mix mixed 30%-50% with sand. Check a few inches into soil for dryness, not surface.

SCALE

SYMPTOMS - Gray, brown, or black flat to ridged bumps on bark, leaves and shoots, sticky dots that may grow sooty mold; leaf drop and stem die-back.

CONTROL METHODS - Insecticidal soap spray by itself or mixed with ultra-light horticultural oil. In summer test a few leaves first.

COMMENTS - Infestations often occur while plants are outside for the summer. Use a soap/oil spray when moved indoors. Check for insects the first few weeks indoors.

APHID

SYMPTOMS - Green pear shaped insects covering bottom of leaves or tender new shoot tips. Sticky honeydew or black sooty mold; leaf yellowing followed by leaf drop.

CONTROL METHODS - Take plant outside and knock aphids off with stream of water. Insecticidal soap or soap/oil mixture.

COMMENTS - Infestations often occur while plants are outside for the summer. Use a soap/oil spray when moved indoors. Check for insects the first few weeks indoors.

SPIDER MITE

SYMPTOMS - Tiny moving dots on webbing, especially on under sides of leaves or around tender new shoot tips. Yellow stippling pattern on top of leaves.

CONTROL METHODS - Mist foliage top and bottom daily, especially when hot and dry. Keep plants away from dry heat source. Insecticidal soap spray, soap/oil mix.

COMMENTS - Infestations often occur while plants are outside for the summer. Use a soap/oil spray when moved indoors. Check for insects the first few weeks indoors. Spider mites thrive and multiply rapidly during hot dry weather.

BIRD

SYMPTOMS - Fruits disappear or have gaping holes in them. Strawberries, blueberries, cherries and filberts are most susceptible but most fruits suffer occasionally.

CONTROL METHODS - Reflective Bird Scare Tape can work well. Bird netting. Cages.

COMMENTS - Blue Jays start harvesting filberts when ready to pick, and so should you. Nuts dropped by jays are usually empty.

VOLE/MOUSE/RABBIT

SYMPTOMS - Bark eaten in a band from soil level up to 8” and roots eaten too, usually in snowy areas with lots of mulch or tall grass at base of trees.

CONTROL METHODS - Keep mulch 4”-6” away from trunk. Keep grass short and 1’-2’ from trunk. Use vinyl tree guard wrapped around trunk until tree well-established.

COMMENTS - Voles and mice will chew a couple inches above ground and also into the root system. Rabbits will chew up to 8” high, particularly apple trees.

ANT

SYMPTOMS - Numerous ants scurrying up and down the tree trunk; aphids, scale or mealybug present in large numbers, lots of sticky honeydew, perhaps sooty mold.

CONTROL METHODS - Find hill and apply pesticide. Apply Tangle Trap over 2-3” wide band of paper wrapped around trunk. Eliminate other pathways into tree.

COMMENTS - Ants nurture and protect these insects in exchange for their sugary secretions. Insects may be difficult to control until the ants are controlled.

BROWN MARMORATED STINK BUG

SYMPTOMS - Poking-type feeding damage followed by decay on fruits, nuts, berries and leaves. Deformity in the healthy tissue surrounding the dead tissue. Brown spots can show up in stored fruit.

CONTROL METHODS - Monitor with traps, some broad spectrum pesticides may work. Researchers are working on finding effective controls, but no info has been released yet.

COMMENTS - BMSB over winters in groups in dry protected areas, such as houses. If you find them on or in your home use the vacuum, squishing releases their defensive stink. See stopbmsb.org for more info. Feeding begins in spring when the weather warms up and continues until new adults go dormant for winter.

RUST

SYMPTOMS - Lesions on the upper surface of the leaf, or on the fruit or stems, followed by orangish structures on the bottom side of the leaf, or on the fruit or stems, which produce spores.

CONTROL METHODS - Copper fungicide after harvest before fall rains and again in early spring for prevention of some\ rusts. Remove and destroy infected parts of the plant. If possible select resistant varieties. Many varieties have not been studied. Cedar-apple rust is a problem east of the Rockies.

COMMENTS - Rust diseases require an alternate host, removing the host (within 900’ radius), applying fungicides, or removing infected parts may help. Check with your extension office to see what rust diseases in fruiting plants may be common in your area, and their alternate host.

SUNSCALD

SYMPTOMS - Vertical splits in bark appear spring or early summer, usually on the south or east side of the tree. Disease or insect infestations may then occur.

CONTROL METHODS - Whitewash trunk and lower limbs with interior latex paint cut 50/50 with water each fall until bark has thickened. Avoid planting in frost pockets or where water collects in winter.

COMMENTS - Injury occurs during pattern of warm days followed by freezing nights. Sap gets stuck in trunk, freezes, then rapidly thaws in the warm sun the next day, rupturing cells.

DEER

SYMPTOMS - Browsed shortened branches. Leaves are obviously munched on or plants are pulled up.

CONTROL METHODS - Fences or cages at least 8’ tall. Plastic mesh, electric, or woven wire fences.

COMMENTS - At Raintree, an 8’ woven wire deer fence has worked best. Repellents don’t work consistently. and only trained large dogs patrolling the perimeter are effective. Some have had success with the product “Deerchaser.”