Palms do not grow in a similar way to trees such as oaks, maples or spruces. Palms do not have bark, a cambium growth layer under their trunk and do not develop complex branching root systems like those seen on toppled trees after windstorms. Palms do, however, grow their roots in the top metre (1 yard) of topsoil like trees and extend their roots far from the trunk. Palm roots neither grow as big as nor mirror habits of their above-ground parts.
Palm root characteristics
With long, tall trunks, it may seem logical that palms might grow from long, deep taproots that resemble carrots. On the contrary, palms develop hundreds of thin roots that radiate outward in all directions, mainly horizontally, from the base of the trunk. Digging down around a palm trunk exposes a highly modified growth region that resembles a bulb at the base of the trunk underground. From it, thin unbranching roots grow to stabilise and anchor the palm and grow into soil for sources of nutrients and moisture.
Root zone size
Palm roots, like those of trees, grow in the top 60 to 90 cm (2 to 3 feet) of soil where warmth, water and nutrients are most plentiful. Palm roots grow outward for great distances, not just a few feet from the trunk, or only to the extent of the farthest reaches of the leaf tips. Large-growing palm species -- such as royal, Bismarck, Bailey and Canary Island date palms -- can extend their roots 15 m (50 feet) away from the trunk. Smaller palms vary their root zone sizes, but a distance of 3 to 7.5 m (10 to 25 feet) from the trunk is a reasonable general estimate.
Palms originate or rejuvenate roots from the growing surface at the bulblike trunk base, 30 to 90 cm (12 to 36 inches) below the soil surface. Cutting the roots of some palms causes the entire length of root to abort, and a new root must grow to replace it. Other palms may sprout a bud to continue growth if a root is cut. Roots become most active when soil temperatures get above 23.9 degrees Celsius (75 degrees Fahrenheit). For these reasons, horticulturists transplant palms by digging a large root ball near the trunk base. Palms establish after planting most quickly during the warmth of late spring to midsummer. A balance exists between retaining as many roots and soil around the base of the palm as possible and making the root ball small enough so that it isn't too heavy to lift and transport to the planting site.
Fertilisation and watering insight
Because palm roots extend far from the actual trunk or multiple stems of the plant, fertilising and watering palms should be mainly at the trunk base. Scatter granular fertiliser far and wide around the palm so nutrients reach roots at various distances from the trunk. Also water palms near the trunk for fastest uptake of water, but also deeply 3 to 15 m (10 to 50 feet) from the trunk to sustain outer, younger and actively elongating roots.