Lemon trees may seem big and strong, but the root system of a lemon tree is relatively shallow. Knowing about the tree's root system is a helpful fact for a gardener making decisions about planting, watering and mulch. Whether you select an ordinary lemon tree (Citrus x limon, USDA zones 9-11) or an Improved Meyer (Citrus x limon 'Meyer Improved,' zones 8-11), you need take care of the roots before you begin counting your fruit.
Lemon Growing Conditions
Growing lemon trees won't present many problems if you're lucky enough to live in a warm climate. They're generally easy to grow and they light up your backyard with exquisite white blossoms, intoxicating fragrance, brilliant yellow fruit and year-round foliage. These little beauties grow outdoors year-round in U.S. Department of Agriculture plant hardiness zones 9 through 11, but you can grow a container plant in far colder climates and bring your plant inside when there's a threat of frost. Your primary concern is to get the roots the nutrients they need when they need them.
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Root System of Lemon Trees
You have to take the lemon tree's root structure into account at every stage of planting and growing. The roots stay largely in the top 24 inches of soil, because a system of woody roots develops laterally from the trunk in all directions, traveling horizontally well beyond the drip line of the tree.
Bunches of fibrous roots grow from the woody roots, and it's these that have primary responsibility for obtaining water and nutrients for the plant. Root growth takes place in "flushes" that occur from February through November. Failure to provide adequate water during these flushes can kill a lemon tree, but too much water can also be dangerous.
Planting Comes First
When you're placing that root ball into the hole you've prepared, keep those roots in mind. Given the spread of the root system, dig a hole using a garden spade or shovel as deep as the root ball but no deeper, and at least twice as wide. Lemon trees require well-draining soil, so amend heavy soil by working in several inches of compost or creating a raised bed.
The top of the root ball should sit just above the soil line. You'll need to keep the root ball moist but not wet until the roots expand into the surrounding soil. Water several times a week, close to the trunk, in the months after planting. Once the tree is mature, you should water further from the trunk about once a week, allowing the soil to dry slightly between waterings.
Mulching Protects and Nourishes
Think of mulch as the soft blanket you tuck around your tree to protect it. Although mulch can consist of virtually any material layered over the soil beneath a plant, lemon trees do best with organic compost or chopped, dried leaves. Spread a 4- to 6-inch layer over the soil in the root zone area, keeping the mulch a few inches from the trunk.
The material keeps down weeds, regulates the soil temperature and eventually disintegrates into the soil, providing nutrients for the tree. It's also a good idea to remove all lemons that form the first few years to allow that energy to be used to strengthen the root system.
Lemon Tree Root Pests
Healthy lemon trees growing in healthy soil generally have few pest problems. But pests and diseases that live in the soil can cause lemon root problems. The two worst offenders are the citrus nematode (Tylenchulus semipenetrans), and different fungal pathogens causing fibrous root rot, including Phytophthora citrophthora and Phytopthora parasitica. Lemon root diseases can kill the tree.
You can help your lemon tree roots avoid these issues by spacing them at least 12 feet from each other and from other trees. This prevents pests from traveling from one tree to another and also limits canopy shading of the soil, which encourages pest populations.