Green Giant arborvitae (Thuja standishii x plicata) is a fast-growing evergreen tree that can fulfill a number of purposes in yards, parks and landscapes. These tall trees make good windbreaks when planted in a tight formation. Too much or too little water can lead to health problems in the arborvitae.
Green Giant arborvitae trees grow in USDA plant hardiness Zones 5 through 7. They reach a mature height around 60 feet tall and a width near 20 feet wide. These trees form a conical, pyramidal shape that presents a uniform appearance on all sides, making a majestic statement as a center plant in the landscape. Green Giant arborvitaes experience few pest or disease problems and tolerate a variety of soil types.
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While Green Giant arborvitaes can tolerate a variety of soil types, these evergreens require evenly moist soil conditions. Although their rapid rate of growth depends on an adequate supply of available water, poor drainage can lead to health problems. The best soil for this type of arborvitae is a loose, well-drained soil. Planting these trees in low areas can cause standing water to damage the roots, while planting them on steep slopes may create a rapid run-off condition that restricts the amount of moisture in the underlying soil.
A healthy Green Giant arborvitae needs slight moisture near the depth of the roots throughout the growing season. The correct amount of supplemental watering depends on your climate and soil conditions. Slightly sandy soils require more frequent watering while heavy, clay soil requires less frequent watering. During dry spells, a weekly, deep watering that provides about 3 inches of water over a period of one to two hours is usually sufficient in medium-textured soils with average to good drainage. Too much water, as well as too little water, can lead to browning of the foliage.
Even dampness near the roots will help a Green Giant arborvitae thrive. The best way to determine the correct amount of water necessary is by digging a small 12-to-18-inch-deep test hole near the outer edge of your tree's canopy. Checking the soil at the depth of the underlying roots will help you determine how frequently to water your trees. The soil against the roots should feel slightly cool and damp at all times, not dry or soggy.