I have to confess I have given the hydrangeas that came with the house very little care and know very little about caring for them. Actually, the deer usually chew them down to ground level every winter and they somewhat magically reappear every spring. This year is different: I still have all the somewhat dried stems and tons of dried blooms from last summer and now I see these stems are starting to bud and I'm not sure what to do...
Should I clip off all the old dried flowers from last season or leave them; should I cut the plant back down, hoping new buds will reappear? Just what should I do now and what should I have done in as much as the deer didn't come through this year?
Hello, michaelangelo. My dried out blooms from last year tend to mysteriously" vanish in January-February most years. If yours are still clinging to the plant, you can deadhead them. You simply cut the thin strand that connect the bloom to the stem. For information on pruning and deadheading, see http://www.hydrangeashydrangeas.com/pruning.html
Dried out stem can leaf out as late as the end of May so it is best not to prune until mid-to-late May. You can prune them all the way down to the bottom. But if you just cannot wait, try pruning from the top of the step in 1" or 2" increments. Stop as soon as you either hit green or get to the bottom of the stem.
Because you live in MN, winter is very cold so the stems usually dry out if you do not use winter protection techmiques. This year, winter has been mild so some stems (or parts thereof) did not dry out. Now they are leafing out and may or may not produce bloomage. They may look weird too because the old stems will be longer than the ones that are now starting to grow from the bottom. But since I like to have the flowers whenever I can, I would live with the weird look until a few weeks after bloom times and then decide if you want to prune them all to the same size.
If you have mopheads, these produce flower buds in July-August and then produce blooms in April-May. It is safest to prune these after they have produced blooms (so you can enjoy then) but before the end of June. Stems that originate from the crown will produce blooms if the shrub reblooms; otherwise, you will get blooms in Spring 2013.
If you have some of the other varieties (oakleafs, paniculatas, etc), those produce flower buds after they leaf out so they can be pruned after they bloom (so you can enjoy the blooms) all the way to around now.
Note that, if the hydrangeas are located in a place where they will attain their estimated size at maturity, you will rarely ever need to prune.
If you want to winter protect so the stems do not dry out and so they flower buds at the ends of the stems survive winter, consider surrounding the shrubs in the Fall with chicken wire at least 3-6" inches away from the sides of the plants and from the top. Then fill them up with dried out leaves, hay, etc when the hydrangeas go dormant or you see of a the very cold front about to arrive. Pack the leaves tight; the more leaves, the more winter protection. Top this with cardboard and use rocks/bricks/etc to keep the top in place. Leftover leaves can be stored in plastic bags and used in mid-winter when settling causes some areas to be exposed to the cold.
Hydrangeas do not need much in terms of fertilizers. They are not heavy feeders and will not react to fertilizers like roses do. For the northern half of the country, try feeding them with 1/2 to 1 cup of compost, composted manure, cottonseed meal or use a general-purpose slow-release chemical fertilize in June. During the growing season, feel free to apply liquid seaweed, liquid fish or coffee grounds if you want. But stop all these types of fertilizers by the end of June so the nitrogen will not accumulate and prevent the plants from going dormant.
If your soil is alkaline, you may notice that the leaves turn yellow but the leaf veins remain dark green. If that happens, you will need to regularly amend the soil with products like aluminum sulfate, soil Sulphur, green sand, iron sulfate or liquid iron-chelated compounds sold at nurseries all over. Of those prodycts, aluminum sulfate is useful if your soil is defficient in aluminum. This will also make mopheads turn blue-ish but be careful not to add aluminum sulfate to rhododendrons or azaleas who just do not like it.
I hope all this helps you. See the other pages of the link above for more hydrangea information.
Given where you live (guessing zone 4-ish?) and the fact that it sounds like deer have chewed your plant to the ground most winters and it's still bloomed the next year, I suspect you have one of the types of hydrangeas that blooms on new wood and therefore it could be pruned now if you wanted to. It doesn't necessarily have to be pruned though, I would probably leave it alone unless it is too big for the spot it's in.