Few trees offer as many benefits as lemon trees (Citrus limon), including fragrant white flowers, glossy evergreen leaves and aromatic fruit. Hardy in U.S. Department of Agriculture plant hardiness zones 9 through 11, lemon trees typically grow from 10 to 25 feet tall and 10 to 15 feet wide when growing in the ground, but dwarf varieties also grow in containers. Lemon trees produce their best crops in sheltered, full-sun sites. Take care when handling the trees because many varieties are thorny.
Lemon trees are ideally suited for sunny locations with well-drained soil. Although they tolerate highly acidic and alkaline soils, lemon trees need fertile, moist soil to grow healthily. These trees perform best in loamy or sandy soils and don't tolerate poorly drained, heavy clay soils. The site should also be sheltered from strong winds, although the trees tolerate moderate exposure to sea air on coastal sites. Multiple trees should be spaced at least 15 feet apart. Lemon trees grow naturally into a rounded, umbrella or vase shape without pruning.
Lemon trees thrive in consistently moist, but not saturated, soil. Remove all grass and weeds from an area 2 feet in diameter around the base of your lemon trees to avoid competition for water. Water the trees when they're actively growing and the soil surface is dry, applying 2 inches of water within the drip lines. Spray the water over the soil surface using a soft spray attachment on a garden hose. Newly planted lemon trees need frequent watering while they establish. To concentrate water at the tree roots, create a basin at the foot of each tree by building a circular ring of soil 2 feet across and 3 to 4 inches high and thick. Water newly planted lemon trees by filling this basin every three or four days for two weeks, then every seven to 10 days for two months.
Regular, small doses of high-nitrogen fertilizer help lemon trees grow vigorously. Feed one-year-old lemon trees when new growth appears in spring. Sprinkle 1/4 cup of ready-to-use 21-0-0 ammonium sulfate over the soil surface within the tree's drip line, and water it into the ground. Apply the same amount of fertilizer three times more, at two-month intervals so that the tree receives 1 cup in total. Feed older lemon trees using the same approach, but vary the number of cups with the tree's age. For example, a two-year-old tree receives 2 cups of ammonium sulfate and a three-year-old tree receives 3 cups of ammonium sulfate, up to a maximum of 6 cups.
Protecting From Frosts
When cold snaps threaten, lemon trees need protection. If temperatures are due to dip below 40 degrees Fahrenheit, throw a blanket, tarpaulin or other covering over each lemon tree. Stretch out the corners of the covering and weigh them down with stones or tie them to the ground with lines and pegs, taking care not to damage the tree. You can also build a simple wooden or PVC pipe frame over the tree to support a covering, and place an incandescent heat lamp beneath it to keep off the chill.
Growing Lemons in Containers
In USDA zones 8 and lower, lemon trees can be grown successfully in containers. Two lemon varieties that grow well in containers are "Dwarf Lisbon" lemon (Citrus limon "Dwarf Lisbon") and "Meyer Improved" (Citrus limon "Meyer Improved"), which grow outdoors in USDA zones 9 through 10. For a young tree, use a container that's about 15 inches wide and deep with drainage holes at the bottom. You can use commercial potting soil for citrus trees or make your own from 1 part pinebark, 1 part peat and 1 part clean sand. Place the potted lemon tree outside in a sunny spot during the growing season and water it when the soil is dry to a depth of 1 inch. Water the soil surface slowly until water flows through the drainage holes and allow the container to drain thoroughly. Fertilize lemon trees in containers with a 5-2-6 citrus fertilizer in late winter, late spring and fall, applying 1 teaspoon per 4 inches of the container's diameter, up to 12 inches, then 2 teaspoons per 4 inches of diameter, or apply the fertilizer according to the manufacturer's instructions. Sprinkle the fertilizer over the soil surface and water it into the soil. Move the lemon tree to a bright, frost-free indoor site when temperatures are forecast to fall below 40 degrees Fahrenheit.