Acknowledgement: Most information in this section has been reprinted with permission by Four Winds Nursery of California, a nursery specializing in citrus trees whose founder was also responsible for the Improved Meyer Lemon. See www.Fourwindsnursery.com for even more information about Citrus.
Growing Citrus in the Ground
Sometimes people aren’t quite sure about using citrus as a landscape plant. In fact, citrus work extraordinarily well in most any landscape, offering beautiful evergreen foliage, lovely (and fragrant) blossoms, and colorful fruit. If you’d like to see some examples of successful landscape plantings, take a look at our landscaping slide show.
Citrus trees grafted on dwarf rootstocks are perfect for container growing but can also be planted in the ground. If planted in the ground dwarf trees can be expected to reach “Semi-Dwarf” size – up to around 16 feet in height, depending upon variety. In a pot, the dwarf trees will stay much smaller, especially with judicious pruning. Standard size citrus trees, available at California nurseries, are best suited for growing in the ground and can be expected to get much taller – up to 25 feet, depending on variety. Be sure to provide more space in the ground for standard size trees. Generally, a Dwarf tree needs an 8-10 foot diameter space, while a Standard tree should be provided with a larger growing space – up to 15 feet in diameter.
In general, ground-planted citrus trees are happiest in warm, temperate areas. San Francisco has 7 main microclimates but lemons can do well in all of them thanks to our mild climate. Fortunately, we rarely have frost.
A sunny, frost and wind-free location with southern exposure is best. (If in doubt, leave the tree in its plastic container and place it in the spot you have in mind. Water as needed, and after a week or two you should be able to tell whether or not it’s happy.)
Reflected heat from sidewalks, walls, driveways, or other structures can help to create a warmer “microclimate.” Avoid planting citrus trees in lawns that get frequent, shallow sprinklings. Don’t crowd your tree, for even though it is a dwarf, it will need room for its eight-ten foot ultimate diameter. The root system can reach far beyond the drip line.
Citrus trees are famous for tolerating a wide variety of soils, including clay. However, good drainage is essential, as citrus trees can’t survive standing water for long. To test your drainage, dig a hole 30″ deep where you would like to place the tree. Fill with water to saturate the soil. The next day refill it with water. Your drainage is OK if the water level drops 2″ in two hours. If the water does not drain well, plant your tree in a raised bed and then amend the soil as described in the following paragraph.
Soils rich in humus are best. For heavy or poor soils, we recommend digging a large hole and filling it back in, half with the best of the original soil, and half with a good-quality amendment mix. Plant the root ball high to allow it room to settle over time. Crown roots should remain visible just above the soil line.
If the plant is growing in a container, gently invert the container to remove the soil intact. Trees that are somewhat dry will usually release more easily from the pot for transplanting. Squeezing the sides of a plastic pot can help to loosen the soil and roots. If planting a bare-rooted mail order tree, shake loose the shavings the roots are packed in before planting. Add the shavings along with your other amendments to the prepared mix for the planting hole.
Take note of the abundant fibrous root system. Straighten out any circling roots and cut off any broken or dead roots before planting. Amend your planting hole as described above. Do not add fertilizer to the soil while backfilling your hole; however, you can apply some to the soil surface after planting. Be sure to tamp soil lightly as you go and water thoroughly after planting to eliminate any large air pockets. Stake the tree as needed until well-established. Green plant tie is a good choice for tying trees to stakes.
Citrus trees are best planted during the active growing season. In summer it is best to plant in the early morning hours when temperatures are cool to moderate. Try to keep the roots out of the sun as much as possible. Water thoroughly after transplanting. If desired, use a solution of Vitamin B-1 Rooting Tonic in the first few irrigations to help fine feeder roots recover more quickly. You may wish to pinch off fruit and blossoms for the first year or two after a new planting to encourage stronger root and branch development.
Consistency is the key with citrus watering! As with so many plants, citrus trees like soil that is moist but never soggy. How often to water will vary, depending on soil porosity, tree size, and temperature. Allowing the top of the soil to dry slightly is OK. A simple moisture meter, available at garden supply stores, can be used to determine moisture down to about a 9″ depth. Generally, when the meter indicates a root moisture level of about 50%, (center of dial) it is time to water. Always store your moisture meter dry between uses to keep it functioning properly.
A wilted tree that perks up within 24 hours after watering indicates the roots got too dry. Adjust watering schedule accordingly. A tree with yellow or cupped leaves, or leaves that don’t look perky AFTER watering can indicate excessive watering and soggy roots. In that case, water less frequently.
In the ground, citrus prefer less frequent, deep waterings to frequent, shallow sprinklings. Creating a watering basin around the drip-line of the tree can aid in deep watering. As the tree grows, be sure to expand the basin as needed to keep it as wide as the spread of the branches. Deeper watering promotes deeper root growth and strengthens your tree. Generally, once-a-week watering works well for in-ground plantings. Be sure to adjust based on weather conditions!
In general, it is probably best to water in the morning, but if plants are dry or wilted it is better to water them immediately, rather than wait until morning. See our watering page for more.
Citrus trees feed heavily on nitrogen. Your fertilizer should have more nitrogen (N) than phosphorous (P) or potassium (K). Use at least a 2-1-1 ratio. Miracid Soil Acidifier is a water-soluble product that works well and is a 3-1-1 ratio. In some regions, you may be able to find specialized citrus/avocado fertilizers. Buy a good brand and apply according to package directions.
Any good citrus formula will contain trace minerals like iron, zinc, and manganese. Many all-purpose products will work. Just add trace mineral supplements if your fertilizer is deficient. We prefer slow release fertilizers in the granular form rather than fertilizer stakes. Follow rates on the package carefully as fertilizers come in different strengths, release rates, and application schedules. We recommend that you fertilize more often than recommended with most slow release fertilizers. Foliar applications of trace minerals in the form of kelp or other soluble fertilizers can be effective. Yellowing leaves indicate lack of fertilizer or poor drainage.
Commercial organic fertilizers can work well for citrus trees. Supplement granular applications with foliar sprays of fish emulsion and kelp. Some people brew compost ‘teas’ which can be helpful when applied to plant roots.
Liberal use of mulches will conserve precious water and help inhibit weed growth. A 2-3 inch layer of redwood shavings, fir bark, compost, or other organic matter can be very helpful for water retention. To reflect heat and hasten fruit ripening, some people mulch with light colored gravel or crushed rock. “Living mulches” such as nitrogen fixing clovers can also be planted between trees in an orchard. To avoid root diseases, always keep grasses and other vegetation away from the root collar area. Keep all mulches at least six inches away from the base of the trunk.
Know where the graft union is on your tree. It can usually be seen as a diagonal scar between 4 and 8 inches from the soil. Remove all shoot growth below the graft. These so-called “suckers” take vitality from the top of the tree (the fruiting wood). Especially on young trees, they are very vigorous. Remove suckers as soon as they are observed. See photos.
Thorns are removed from rootstocks when they are grafted. Juvenile fruiting wood will sometimes have thorns. This is a young plant’s way of defending against grazing animals. As the tree matures, thorns will not appear as often. Prune off thorns if desired.
Citrus may be pruned as desired to achieve the look you want. Pruning is fine any time of year, except in the winter for outdoor trees. Pinching back tips of new growth can help trees to maintain a round form, without impacting future fruit.
Citrus will look fuller with occasional pruning to shape leggy branches. Very leggy branches can indicate the need for more light (etiolation).
Some trees may develop erratic juvenile growth above the graft. Don’t be afraid to completely prune off an erratic branch if it is too irregular or crossing another branch. Other fruitful branches will replace it. Any growth above the graft can eventually bear fruit. Well-pruned trees have higher fruit yields and are less prone to branch breakage.
Citrus are self-pollinating, even indoors. Some people enjoy pollinating their trees and can do so by using a small soft brush or cotton swab to transfer pollen among the flowers.
Citrus trees can be trained fairly easily to grow on trellises. Simply use green garden ties to hold branches in place and prune to encourage desired branching patterns. Select specimens with an open growth habit that will most closely match with your intended espalier design. See this link for some tips on espaliering citrus trees: http://www.gardenguides.com/118929-espalier-citrus-trees.html
Spiders, lady beetles, lacewings, and preying mantids (praying mantis) are just some of the beneficial critters you may see around citrus trees outdoors. You can even buy some predator insects in local nurseries for release in your garden. See this link for an overview: http://groups.ucanr.org/MGPG/Good_Bug_Bad_Bug_Articles/.
One reputable source for beneficial organisms is ARBICO.
It is important to keep your tree free of ants, because they will “farm” scales and other honeydew-producing pests, moving them from place to place, milking their secretions, and protecting them from their natural enemies. Ant baits that contain boric acid may be helpful. A recipe for a homemade ant spray can be viewed here.
If you find harmful insects like scales, aphids, or mites, a household spray bottle of water with some mild dish soap could be all you need. Orange TKO, an organic cleaner, works very well at a dilute rate. You can also find specially formulated Horticultural Soap products at local garden centers. Use a soft toothbrush to scrub away adherent scale insects and recheck in a week to see if another treatment is needed. If scale insects persist, the usual nursery treatment is a 1% solution of light horticultural oil. Learn more.
Many citrus varieties can tolerate temperatures as low as 32 degrees for 2-3 hours. Even temperate locations can drop below freezing so it’s good to have a plan of action ready. Old fashioned Christmas lights (that produce some heat) can be effective, either alone or in combination with frost covers. Anti-transpirant sprays such as ‘Cloud Cover’ can also be effective when used according to directions. Straw mulches, cloth covers and even plastic sheeting can be combined as needed to provide the necessary level of protection. See this link for more on frost protection options:
Problem Solver: Best Varieties for Indoor Growing
By far, the Meyer Lemon is the most popular. Like all the lemons, it is easy to grow, prolific and does not need a lot of heat to ripen the fruit. The Meyer is slightly sweeter than the classic commercial varieties (Eureka and Lisbon). Its soft skin develops an orange hue when fruit is fully ripe, and its distinctive, mystical flavor combines lemon with a hint of tangerine. The Meyer lemon can be very productive, even indoors, and does not need a lot of heat to ripen the fruit.
The Variegated Pink lemon is a gorgeous plant that will also do well indoors. The trees are slightly larger than the Meyer and are very attractive with variegation in the foliage and young fruit. Flower buds and shoots of new growth tinged with fuchsia.
Of the oranges, the Trovita is most suitable for indoor growing. Trovita ripens in the spring, so it can often be taken outdoors to finish sweetening the fruit.
Kaffir Lime leaves are used extensively in Thai and Cambodian cooking, and zest of the fruit is an ingredient in some curry paste recipes. Keep your Kaffir lime tree close at hand in a sunny window and you’ll be able to create authentic recipes year-round.
Calamondin (Kalamansi) is a diminutive tree originating in the Philippines. It’s ornamental form, fragrant blooms and small tart orange-colored fruits have made it a favorite for centuries. The sour juice of ripe fruits can be used in salad dressings and other recipes.
Oro Blanco Grapefruit is the sweetest white grapefruit, and most tolerant of indoor growing. Provided adequate conditions indoors, it produces edible fruit without the high heat usually necessary for grapefruit. See our Citrus Variety Information Chart for additional information by variety.
Problem Solver: Growing Dwarf Citrus as Indoor/Outdoor Plants
Container-grown citrus trees can be kept on patios and decks in warm weather, then moved inside to avoid frost damage in winter. To avoid shocking your tree with a sudden change of environment, move it gradually. Place the tree in partial shade for a week or so, to make the transition from full sun outdoors to partial sun indoors. It is best to let the roots get a bit dry before moving trees indoors, to ease the transition and reduce the chance of roots staying too wet through the winter. Later you can reverse this process after any danger of frost has safely passed. You will find that you need to water less indoors. A moisture tester will help prevent over watering. See this page for watering guidelines and recommendations.
If your tree will receive less than 6 hours of full sun per day indoors, it is best to supplement with grow lights. Adequate sun exposure is important for fruit production. See this link for helpful information on grow light systems. Some lemon enthusiasts have reported having good success supplementing with “PAR-38″ LED grow lights. They are convenient to use because they screw into a common light fixture socket. They are available in several wattages and roughly match the absorption spectrum of chlorophyll.