Averaging 3 feet of growth in one year, Leyland cypress trees (X Cupressocyparis leylandii) can grow up to 70 feet tall in preferred U.S. Department of Agriculture plant hardiness zones 6 through 10. Because of their astounding potential size, these conifers need full sunlight conditions for optimal photosynthesis. However, spacing your Leyland trees apart by only 2 feet creates a number of issues, including a different growing habit compared to its traditional tree form.
As a hybrid variety of Alaskan cedar and Monterey cypress trees, Leylands have a natural pyramid shape to their foliage, much like a standard Christmas tree. In fact, its base spread often stretches to 25 feet or more. When you plant these trees within 2 feet of one another, the branches quickly intertwine to form a hedge. If you diligently prune the Leyland trees, they will remain in this shape for privacy usage in the yard. Even hedge formation planting, however, requires a larger spacing of 4 to 10 feet for a healthy tree environment -- competition for natural resources may cause stunting and dieback with this spacing measurement.
Branches naturally rub against one another as they grow closer with a 2-foot spacing. This rubbing slowly degrades the bark and exposes the tree's interior to the weathering elements. As a result, fungal diseases, like various canker types, invade the vulnerable limbs. Two particular diseases, called Bot and Seiridium canker, actually seep contaminated sap from the sores so that other portions of the tree may be infected further. For both diseases, the foliage turns a dark color as the individual limbs slowly dieback. In these cases, it is necessary to remove the diseased limbs before the fungus spreads. Spacing your trees farther apart prevents excessive limb rubbing for a disease-free Leyland.
Although Leyland cypresses tower over the ground, their root system remains shallow and wide -- feeder roots find better nutrients and moisture within the top 12 to 24 inches of soil. However, a close planting of Leyland trees forces the individual roots to compete with one another. This competition issue is compounded with the addition of ground cover, such as grass, near the tree grouping. As a result, your Leylands display stunted growth from lack of moisture and ample nutrients. Removing the ground cover and widening the planting distance allows the trees to have more room for healthy growth.
If you try to grow other plants, from grasses to small shrubs, under the closely planted Leylands, reduced sunlight exposure becomes an issue. Plant any decorative base plants away from the Leylands and choose varieties that prefer shady conditions for successful growth. Dense needles envelope the trees while blocking almost all sunlight, especially when planted 2 feet from one another.