Answer: In general, hydrangeas do best in a rich, moist yet well drained (not soggy) soil and appreciate some extra water during hot dry periods in the summer. However, there are several types of hydrangeas, and without knowing which type you have it's a bit difficult to make a guess as to why it's not blooming. Some hyrdrangeas, such as the oak leafed, do not bloom all that well at an early age and will not bloom following a severe winter. Other types, such as the macrophylla (big leaf), bloom only on old wood and should not be pruned except in spring immediately after flowering. If the big leaf type is killed to the ground during the winter, it will not bloom the following year. Still others, such as the smooth hydrangea "Annabelle", bloom on new growth and do best if cut down very short each spring.
The biggest frustration gardeners face when growing wisteria is that plants have a longer than average juvenile period and sometimes fail to bloom as expected. If you start with grafted plants or those produced from cuttings rather than those grown from seed, your plant will flower earlier in its lifecycle. A plant will also fail to bloom if: it does not receive full sunlight; there is excessive vegetative growth that may have been stimulated by excess nitrogen fertilizer; it is pruned heavily in winter and spring, which encourages vigorous, vegetative growth; and/or it is pruned improperly. Also, in severe winters, flower buds may be injured or killed. The following practices may help induce non-blooming vines to flower: a heavy application of superphosphate (0-20-0) in early spring (3#-5# per 100 square feet), and severe pruning of new growth in late spring or early summer, followed by root pruning in late fall. Root pruning is sometimes done in late fall to stimulate young plants to bloom or to restore blooming on older plants. It serves to check top growth and favor flower production. Use a spade to cut vertically into the soil (about 18 inches deep) and about four feet from the main trunk, all around the vine. I know you're frustrated, but resist the urge to prune your plant down to the ground! Do a little tip pruning this summer and some root pruning this fall. Hope this information helps!
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