Whether you grow it on a trellis or pole, use it to hide an ugly wall or fence, or plant it because of its flowers, clematis (Clematis spp.) is a garden multitasker. More than 250 clematis species, cultivars and hybrids exist, and, depending on their variety, they are hardy in U.S. Department of Agriculture plant hardiness zones 3 through 8. Planting preparation is the most important aspect of success with clematis.
Spring is best time to plant clematis, but it also can be planted in fall, provided it has time to become established in the ground before cold weather arrives. Too much heat at planting time may cause the clematis stress beyond the stress of being transplanted. So plant it on a day when the temperature is lower than 85 degrees Fahrenheit. Choose a clematis plant that isn't blooming; the plant needs to devote its energy to becoming established, not producing flowers. Bare-root clematis plants should be planted in spring while the plant is still dormant.
Clematis requires a minimum of six hours of sunlight each day and prefers its roots to remain cool. If it gets particularly hot during summer where you live, then choose a planting location that offers protection from direct afternoon sunlight. The flower colors of some of the red- and blue-flowering hybrids fade when they receive too much direct sunlight; examples of such hybrids include "Nelly Moser" (Clematis "Nelly Moser") and "Hagley Hybrid" (Clematis "Hagley Hybrid"), both of which are hardy in USDA zones 4 through 8. Choose a site with an eastern sun exposure for these types of hybrid clematis. Planting the clematis where it receives air circulation through and around it will help it ward off fungal infections.
Prepare the soil properly, and you'll be repaid with a healthy clematis that blooms all season. Clematis prefers a well-drained site that is moist but not soggy. Amend the soil in the planting area with an 8-inch-thick layer of organic material. The material can be compost, aged manure, fine bark, peat moss or a combination of any of those. Combine the amendments with the existing soil to a depth of 2 feet.
Clematis roots roam and don't like to be disturbed, especially small-flower types. Ensure they will have plenty of room in the planting location and remove the plant carefully from its container to disturb the root system as little as possible. Providing the plant with a large planting hole gives it a successful start. The hole should be deep enough so that when the clematis is planted, its crown – where the main stem joins the roots -- sits 2 inches below the soil surface. Dig the hole twice the depth required to meet that goal and twice the width of the clematis' container. Set the plant's roots in the hole, and fill the remainder of the hole with the planting site's amended soil. Insert a 1/2-inch-diameter stake 2 to 3 inches into the ground 2 to 3 inches from the plant.
When planting more than one clematis, spacing the plants based on their mature size is important. If, for example, the clematis plants you've chosen are 3 feet in width at maturity, then plant them at least a few inches more than 3 feet from each other. Use one-half a plant's mature width when determining how far from a wall or other structure to plant it. Bare-root plants should have the root system soaked in a bucket of water for approximately one hour before planting.
Care During Establishment
Immediately after the clematis has been planted, its soil needs to be watered until it is saturated to the depth of the plant's roots. The planting site requires 1 inch of water each week, either through rain, irrigation or a combination of both. Keep the root system cool by adding a 2 inch layer of mulch over it or planting a non-aggressive ground cover with a shallow root system on top of the planting area. Although the clematis should twine naturally around the stake you inserted in the ground, leaning the plant against the stake will encourage twining.