How to Prune Your Hydrangeas
First, Why Is Pruning Necessary?People always hate pruning their plants back, especially when you are cutting your plants back to what seems like almost nothing. But every time you cut off a single stem it will branch and produce two or more new stems right below that cut. Then the next time you prune you will cut back those two new stems to about three inches long and again get two branches on each, or four total. Then next time you prune those to about three inches and get eight stems and so forth. The earlier you start pruning plants back hard the better because you want that heavy branching to be low down on the plant to get a nice rounded look. If you wait to start pruning until plants are very large then you end up with very few low branches and lots of short nubby stems up top. For Hydrangea plants, we have found that cutting plants back hard to only about six inches tall is a much better alternative to selective pruning because plants end up more evenly rounded despite your tedious clipping. Plus you can prune the whole plant in about 40 seconds when cutting them back hard rather than in twenty minutes when cutting stem by stem. Hard pruning is how we prune almost all plants at our nursery and they always look great with full, rounded forms. In fact, small Hydrangea plants (and most other woody shrubs as well) that we are only growing up to larger sizes and flowering is not important get pruned back like this three or four times a year to maximize dense branching.
After a few years of hard pruning your plants will be very dense down low and you can switch to just pruning the outside to maintain an ideal shape. All you really need to do is cut back portions that are growing disproportionately faster than other parts of the shrub to keep it in good order. If the plant gets really out of hand then go back and prune it to about six inches tall again to rejuvenate the plant.
Timing Is Everything For HydrangeasThe first thing you need to know about your Hydrangea plant before starting pruning is which type of variety you have. Depending on the flowering cycle of your particular variety you are either going to want to prune in early summer right after flowering is done or in winter after plants go dormant. Pruning at the wrong time can yield poorly flowering plants because you end up cutting off all the flower buds before they produce any flowers and after the plant has finished making flower buds for the season. There are basically three types of flowering types, those that flower on old wood, those that flower on new wood, and those that flower on both. The varieties that flower on both are newer and are a fantastic addition to gardens because they tend to bloom longer and there is less risk in pruning incorrectly.
Old Wood Varieties - These Typically Flower in Early Summer
Many Hydrangea species flower on previous year's growth, which means that in the late summer buds develop on the new stems that contain the flowering tissue for the following year. These buds remain dormant through the entire winter and then grow the following spring, produce a small length of stem with leaves, and then end with a single large flower at the end. Other buds will develop at various points in the year to produce leafy growth but most of the time these will not produce any flowers - yet. Of course, all the new leafy growth will produce buds at each leaf junction and many of these will produce the flowering stems next year. If you cut Hydrangea varieties that bloom on old wood back in the winter really hard, you end up cutting off almost all the buds that are ready to produce flowers the coming summer. So the time to prune old wood Hydrangeas is right after they have finished blooming in mid-summer. You can cut all the stems back almost to the ground, leaving a few good healthy buds on each, and get your plants to flush out with dense growth around June or July. Your plants will look great and the new growth will produce tons of buds all along the stems that contain flowers for next summer, so you will get very strong flowering again next year. And then after next year's flowering you can do the same thing and cut your Hydrangea shrubs back hard again. New Wood Varieties - These Typically Flower in Mid to Late Summer Unlike varieties that flower on old wood, new wood varieties produce new growth in the spring and then at that point develop flower buds quickly and bloom. These plants can be cut back to any height during the winter and still flower that same year, but you don't want to prune in the spring or summer. This is also great for gardeners in very cold climates because the flowering buds don't have to overwinter and so cold damage is not an issue for blooming. If you have a Hydrangea plant that seems like it never blooms then most likely you have an old wood blooming type that is not hardy enough for your area. Consider replacing it with a new wood flowering type! New and Old Wood Varieties
Some varieties, such as 'All Summer Beauty' Hydrangea, produce flowers on both old and new wood. The benefit of growing this type is that it blooms in two seasons, once early in the summer and then again in late summer. Pruning is best done right after plants finish blooming in early summer, but you can also prune plants in the winter.
Deciding Where To CutAfter determining the correct season for pruning your specific Hydrangea species, you must figure out where to make the actual cuts. Typically you want to make the cut in growth that is one season or younger right above the lowest node with large buds. Make the cut half to one inch above the buds, which is high enough that you don't damage the buds but low enough that you don't leave an ugly nub.
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