Thuja Green Giant and Leyland Cypress trees will tolerate partial shade. We want to discuss the overhead Canopy, shade on one side, the impact of how being in the South vs North can effect a shady planting site. We also will cover the symptoms of too much shade, pruning the canopy shade trees and also recommend a good substitute for shady location privacy screens.
A straight overhead canopy of shade is not the best situation for Thuja Green Giant or Leyland Cypress trees. The least desirable situation is an overhead evergreen or pine canopy, because the trees under an evergreen canopy don’t even get sunlight during winter. If that is your application, don’t plant there! Sometimes it cannot be avoided. For example, in Long Island and in the Hamptons area, some neighborhood have rules about what can be cut and are very strict about cutting native trees to replace with anything not native to the area. Even so, I am not recommending planting Leyland Cypress or Thuja Green Giant trees under a canopy. I have planted these varieties under a canopy that was very high and still the shade effected the trees.
Northern locations tolerate shade better than southern locations if from decidious trees! If the shade trees are deciduous tress, at least after those canopy trees shed their leaves, the Thuja Green Giant trees will get full sun all winter. This is more beneficial from NY and northward than in southern states, because they shed about five weeks earlier in fall than southern trees and don’t green up until one month later than southern deciduous trees. On Long Island, Thuja Green Giant or Leyland Cypress trees planted under a partial canopy of scrub oaks may get full sun for seven months of winter before leaves re-appear, whereas southern states with a similar situation may only provide five months of full sun. Shade on one side of your row is normally fine, because your Leyland Cypress trees will still get the powerful straight overhead sunlight. Thuja Green Giant or Leyland Cypress trees can grow three feet per year if fertilized properly, so remember if one side of your row has shade from slower growing species, The Thuja Green Giants or Leyland Cypress will outgrow the slower trees shading trees in most cases and therefore eliminate the problem.
There are two major symptoms of too much shade;
The first is the trees thin out. At first planting if Ball and Burlap field grown trees, they will be thick at first. Over the years, shady applications will take their toll and they will thin out somewhat. The second symptom of too much shade is slow growth rate.
Providing light by pruning the offending shade trees is a great idea! If you cut limbs off an evergreen tree that is shading your Leyland Leyland Cypress row, those limbs will not grow back so it should be a one-time effort. If your arborists trim deciduous trees like Oaks, Maple trees, it is more likely to require trimming again at a later date. If the limbs on deciduous trees are cut all the way back to the trunk, on the side that shades your Leyland Cypress trees you may solve it completely. The advice here is do the tree surgery overhead before you plant the privacy hedge beneath. The arborist will probably be able to let the limbs to fall if it is done before installing the Thuja Green Giant row, but if you wait till after planting, the arborist will likely have to rope the branches down to avoid damage on your privacy screen below.
A good substite varieties are Nellie Stevens Hollies for shady applications in Zone 6 and Canadian Hemlock if located in zone 5.. Also remember, when you plant in a mature woodland, the trees nearby not only steal sunlight but will have established root systems that will compete with your new plants for moisture.