Now is a good time to start your spring pruning chores. I will write this series over a period of weeks to coincide with pruning time for some of the more confusing plants in your garden in the hope that I can demystify the process. Among the first plants to get my attention in March are clematis.
Clematis that flowers from late spring to early summer (late April to late May) belong to Group 1 and these plants bloom on last year’s wood. Varieties that I grow from this group are ‘Prinsesse Alexandra’ and ‘Josephine.’ I only do a minimal pruning at this time in order to protect the bloom. First, I remove the winter-damaged stems and then I thin out shoots because there is always a dense tangle of stems. Then I look at individual stems and remove the ones that are too long by cutting to a pair of swelling buds. To keep your plants healthy and thriving you should hard prune all shoots to the base every three years and this can be done after blooming to assure a bloom the following year.
Group 2 clematis flower twice a year…or continuously: in early summer (mid to late May), on last year’s wood, and again in late summer (September into October) on new shoots. Varieties that bloom continuously put out flowers from June to September. The varieties I grow are ‘Jackmanii,’ ‘Mer. President,’ ‘Multi Blue,’ and ‘Henryi.’ The key to successfully pruning plants in this group is: prune to stimulate new growth while retaining the old-wood framework and preserving spring blooms. To keep the plants looking neat, I always cut to a pair of buds. Pruning can be staggered over the season, doing only some shoots at a time. Hard pruning every three years is also recommended.
Finally, there is Group 3 which includes clematis that flower from late summer to fall. ‘Sweet autumn clematis’ is probably the best-known variety in this group but since this is an invasive variety and grows to massive size I do not have one in my garden. Young plants can be pruned in the same way as plants in Group 1 and established plants should be hard pruned every year.