English ivy is well known as an aggressive and attractive ground cover. It spreads by means of branching shoots and air roots that generate a sticky substance, making it easy for English ivy to climb. The rate and thickness with which it spreads has led some to regard it as an invasive vine. Understanding the root system of English ivy helps you control this useful but aggressive plant and prevent damage to other plantings.
Roots and Shoots
English ivy relies on a combination of main, soil-based roots, which nourish the major stems of the plant, and air roots formed along the branches. As shoots form, air roots produce a sticky substance that helps them climb and adhere to surfaces, as well as contribute to plant photosynthesis. Long shoots of English ivy resemble millipedes, with roots along both sides of the stem at frequent intervals.
Clinging and Climbing
The sticky substance that helps English ivy air roots cling to surfaces allows shoots to extend for 20 feet or more in search of sunlight and water for nourishment. Roots are very shallow, leaving a centipede-like pattern on stone, brick or stucco walls if removed. Anchors are strong and frequent enough, however, to enable the vine to climb to great heights. Frequent branching of shoots spreads the weight burden of the air roots over wide spaces.
English Ivy and Other Plants--Vertical Growth
While ivy roots are shallow and therefore less likely to cause severe damage to buildings than some other climbing vines, the wide spread of English ivy and the frequency of its air roots can make it a genuine menace to trees and large shrubs. The ivy's blanket-like spread allows leaves to block sunlight and water intended for the host plant. The rapidity with which it grows can smother or crowd out leaf formation, weakening the host plant's ability to nourish itself.
English Ivy and Other Plants--Horizontal Growth
English ivy's rapid growth and ability to squeeze out other plants account for its reputation as a no-weed ground cover. Shallow roots spread constantly because English ivy takes nutrition only from the very top of the soil. While this may have the advantage of crowding out opportunistic annual weeds, it also has the disadvantage of making it difficult to establish other ornamental plantings, whose new roots and growth stand in constant danger of being swamped by aggressive ivy.
The key to maintaining English ivy with other plants is stringent control of its growth. Heavy pruning needs to be frequent. Ivy that is beginning to climb trees needs strong discouragement. Cut a band around the tree, pruning major stems to within one to two feet of the ground and clearing an area of at least two feet between major stems and shoots. Once shoots die off, pull them down. Add rigid borders to ground-cover plantings and prune ivy within limits whenever it begins to stray.
Control and Consistency
Persist in reducing the impact of English ivy on your overall landscape. This vigorous plant is truly opportunistic. When removing sprouts, shoots or rooted plants, dispose of them in the trash, rather than in the compost heap. Parts of stems and even single leaves possess enough vitality for formation of new plants.