This Jackmanii Clematis is roughly 9 years old and clambers up the side of my deck, facing west.
The Jackmanii Clematis is a modern hybrid clematis with large showy blooms which can be as large as 5-6 inches across and are a magenta to deep purple. The Jackmanii clematis was produced by nurseryman George Jackman (1837-1887) of Jackman & Sons, Woking, Surry, and was available on the market in 1862.
Growing to heights of near 20 feet tall and four feet wide, the Jackmanii Clematis is a superb vine offering masses of purple blooms on healthy twining vines. A suppport, such as a trellis, is essential for the clematis to climb. The Jackmanii Clematis requires 6 hours of direct sun a day to achieve optimal blooms.
When selecting your plant, choose one with several vines coming from the root, preferably with the lower portion somewhat woody to ease the transplant process. Carefully remove from pot and dig a hole about 18 inches deep. Amend with compost and sprinkle a scant handful of bonemeal in the bottom of the hole and cover this with a bit of soil before adding the vine. Plant the clematis a foot deeper than it was in the pot so the roots are well shaded and cool. Fill with good, well-draining soil, amended with compost, gently but firmly tamp down to remove any air pockets, and water. Gently aid the vines to the trellis so they fan out in a "V" formation. In two weeks, you may fertilize with a water soluble fertilizer. (See fertilizer below).
It is highly recommended to plant a low growing perennial in front to further shade the roots and keep them cool. I use irises for this purpose. In lieu of planting, one may use a large flat rock placed in front to further shade the roots. A mulch of a couple inches is highly recommended as well.
Compost and bonemeal should be added yearly, digging in to just the top couple inches so as not to disturb the roots. You may also fertilize monthly from early spring until the clematis begins to flower, with a fertilizer designed specifically for clematis and vines or with a general purpose 20-20-20. Do not fertilize once the vine begins flowering or all the blooms will come at once and the vine will not flower continually until frost.
Jackmaniii clematis belong to the "C" group, meaning they bloom during summer and autumn and should be hard pruned above second or third set of the buds, 20 - 50 cm (approximately 1 foot) from the ground in late winter or early spring. I generally wait until I see new growth, then prune back to the second set of buds.
Jackmanii is one of the most hardy clematis and a very popular choice with few if any insect problems and rarely any instances of disease. Clematis wilt is a problem known to affect any variety of clematis and can generally be avoided by planting the clematis deep to keep the roots cool, as indicated above. Garden sulfur is the recommended treatment. I found a good article here for further information.