|Simply saying a plant will grow in the shade is too simplistic a statement because not all shade is the same. There is filtered shade, partial shade, open shade, and dense shade. Shade changes with the time of day and from year to year as trees grow. Sites that might be in full sun part of the year may become heavily shaded as the season changes or as trees leaf out. Light is also influenced by topography. For example, a south-facing slope receives more light than a north-facing slope.
Types of shade
Many shade plants are native to wooded areas and grow best in soils exposed to decomposing leaf litter and compost. Moisture in shaded areas is different than sunny areas. The cooler temperatures and less exposure to wind decrease water loss. However, competition from tree roots and the large, tender leaves of many shade-loving plants can cause moisture shortages. Trees vary in their competitiveness for soil moisture. Some shady sites can be quite dry. Many plants will grow in the direction of the strongest light; one side of the plant will be thick and full while the other side will be sparse.
Tree shaded gardens become more shaded with time. As trees grow taller and wider they cast larger shadows and less light will penetrate the increasingly dense shade. The quickest way to admit more light is by removing lower tree limbs thus raising the height of the shade. This will decrease humidity and allow some filtered light to reach understory plantings especially in the morning and afternoon.Canopy thinning involves selectively removing trees limbs. This could involve removing a few, large limbs or many, small limbs throughout the tree. The results is a less dense shade or even perhaps a dappled sun-shade situation. Thinning is not a one time procedure; it will need to be repeated as trees grow. The same process can be used on large shade-casting shrubs. Some shrubs can be pruned into a tree form thus allowing more light to plants growing near their base.
Article written by Patsy McNatt, Extension Master Gardener Volunteer.