Answer: Weigela is a spring bloomer that blooms on old wood. Therefore it should be pruned soon after it blooms, before it sets buds for the following year. If pruned in the early spring, before it blooms, you will lose much of the bloom. If you prune too late in the summer, you will be cutting off branches that have already set buds for the next spring. Pruning soon after bloom is ideal.
General guidelines for pruning include: pruning out all dead, damaged or diseased wood. Prune out crossing limbs as well as limbs that are growing in an awkward direction. Prune out suckers or water sprouts that are directly vertical. Then, to rejuvenate an older shrub, prune out up to one third of the oldest stems down to the ground. To reduce the size of the shrub, use "heading back" cuts which reduce individual stems by a quarter or a third of their length. Always prune these stems back to an outward facing bud. And never leave a "stub". Trim back to within about a quarter inch of the bud. If left too long, any excess stem will eventually die back and become a harbor for disease and/or insects.
Roses can be pruned in early spring just as they begin to show signs of life. Follow the same general guidelines as listed above for weigela. Some thinning cuts to get rid of overly long canes can be made in mid-spring. If your rose is not sufficiently hardy for your zone, then cut back in fall enough to accommodate tying and heavy mulching, or use a rose cone to cover.
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