For the second consecutive year my clematis Pamela Jackman, while still putting on the usual masses of stems & lush foliage, has declined to flower. It has flowered in the same (unchanged) spot for over 10 years – I don’t fertilize by the way. A companion clematis (Pilu) is not flowering this year for the first time but a neighbouring clematis – Multiblue – is flowering its head off! No noticeable frost damage; soil moisture same as usual; not in any shade still; no new plants added or removed; no shrubs particularly close. What’s going on?? (pic is from 5 years ago)
A lovely plant. Easy to see why you want it to flower again!
It may be that the soil in which your Pamela Jackman is growing has finally run out of nutrients and that you should fertilize as lack of nutrients is one of the reasons that clematis will fail to flower. Clematis are considered to be heavy feeders so you should consider taking some steps to add nutrients on a regular basis. In the fall or early spring mulch with a mixture of compost, well rotted manure, bone meal and a general purpose organic fertilizer. As well, application of a high-potash liquid fertilizer, for example a tomato fertilizer, or fish emulsion, in early to mid spring will encourage flowering. Another reason for no blooms is too much nitrogen, which encourages green growth but may reduce flowering. This could happen as a result of runoff from a lawn which is being fed. You might consider doing a soil test near your clematis to try and determine what the problem is. Once your plant has flowered again, you could stop fertilizing unless it again fails to flower, although as clematis is a heavy feeder an annual top dressing the fall of compost, manure and bone or blood meal would be appropriate.
Here is a link to a piece on the International Clematis Society on what to do if a clematis is not blooming which you might find informative: https://clematisinternational.com/careindex.html