why don't my hydrangea bushes bloom?
My hydrangea bushes are very attractive plants, but do not bloom. Why? How often should they be fertilized, and with what type of fertilizer?
Delaware County Ohio
Your hydranagea is a macrophylla hydrangea. It is really a zone 6 plant that is tender in most of Ohio. The problem is not you. It is most likely the winter warm-ups we are getting. We had a really cold November, with a warmer December and then warmer in late winter/early spring. This was followed by hard frosts in April. These frosts were widespread. These frosts were probably the issue that affected your plants, as they affected mine. These macrophylla hydrangeas leaf out too early - many times in late March and early April when we still get hard frosts. When a hard frost happens, it kills the flower buds and the tender leaves the plant put a lot of energy into. Even more energy is drained from root reserves to help the plant re-leaf out for the season.
This could be influenced by other factors, too, including too much nitrogen fertilizer. Just like tomatoes, heavy N applications (like liquid fertilizers or lawn fertilizers that got over to the plants) can make the plant focus on vegetative growth (green leaves) vs. flower production. In general, avoid fertilizing these plants with a high N fertilizer (if you are fertilizing).
Location of these plants are also a big factor in their ability to bloom on a regular basis, as is soil type. They should be located in an area where the soil is fertile with lots of organic matter. They should get 3-4 hours of sun in the morning, with dappled shade after 11am for the rest of the day.
My H. macrophylla rarely bloom heavy, mostly light and every couple years – and fantastic last year because of the wet year and mild spring. This year I have no blooms because I live in a frost pocket. I could move them to the front of the house, but the sun is too hot there.
If you have this problem every year, consider cutting them back in the fall. Wait till all of the leaves fall, then cut the stems above the third bud. You can cover it for the winter with mulch, but you will have to keep up with the squirrels and chipmunks digging the mulch back away from the plant. THE MOST IMPORTANT thing to do, though, is to cover/uncover the plant in late March (or as soon as it starts to leaf out) until the last frost. Only cover it on nights where there is a threat of freeze/frost. This would be covering the plant with a non-plastic cloth (like a sheet, etc). Be sure the edges are held down with rocks or sod staples. You need to remove it as the sun begins to heat up for the day in mid-morning. This year it was late April when we lost many fruit crops in Ohio. I bet the same frost hit your plant hard.
Your other option is to choose a Hydrangea serrata. This is a more hardy type of hydrangea that does not leaf out as early as the macrophylla. It is just as beautiful, but not the heavy mophead blooms. The blooms are more lacecap type blooms, but still very full and colorful. There are more fertile flowers within the flower heads that attract pollinators.
Here are some examples of H. serrata (you can search for more here before going to your local garden center). NOTE - This is not an endorsement of a product or specific cultivar - just a n example of some H. serrata type hydranges.
For fertilization, you can fertilize with a general, all purpose fertilizer a few times during the summer. Beware of fertilizers with a high first number. That is the number for Nitrogen. As noted above, this can cause too much foliage with few or no blooms on these plants.
The other option for many, many beautiful hydrangeas are looking at the other four major types that grow in Ohio. You can read my factsheet on these at http://go.osu.edu/hydrangeafacts