You say you live where it’s cold, so the blue hydrangeas you plant never flower? Do you want to grow mophead or lacecap hydrangeas but you’re just a bit too far north? The solution is to grow these wonderful shrubs in containers.
First, get a large pot that’s light weight. Choose a good looking one because these attractive plants deserve a pot that enhances their appearance.
Next, be sure your container has drainage holes, and don’t cover them with anything. Use a good quality potting mix (I use COAST OF MAINE INC – Premium Blend Potting Soil, 8-Qts. or Espoma AP8 8-Quart Organic Potting Mix) and plant your hydrangea, filling the entire pot with soil from bottom to top. Don’t put rocks, shards or mulch in the bottom first. (If you think you need that “for drainage, you really need a copy of Coffee for Roses: …and 70 Other Misleading Myths About Backyard Gardening !)
I also mix a handful of organic fertilizer into the potting soil before the pot is filled. Once your hydrangea is planted in the pot, water it well and place it will get at least 2 hours of sun, but not in the hottest part of the day. Hydrangea flowers last longest when they are protected from mid-day sun.
Water your potted hydrangea deeply and well when it’s dry, and then wait until the surface of the soil starts to dry before soaking again. On hot days you might be watering every day, but in cooler weather every three or four days. Don’t let the plants get too dry and wilted or the flowers will brown prematurely.
Most potting soils are neutral pH which will produce pink flowers on the varieties that are changeable when in acid or alkaline soil. To keep your blue hydrangeas blue, use Aluminum Sulfate such as Bonide 705 Aluminum Sulfate, 4-Pound mixed at the rate according to the package. Know that the change doesn’t happen quickly, so give it a few weeks to work.
In the fall, once the leaves color and fall off of your plant, pull the pots into an unheated garage or other space that’s cold but doesn’t go much below 35 degrees. Check the soil every couple of weeks and water if it’s dry, but leave it alone when it’s still moist. Don’t cut the canes of mophead or lacecaps down at this point – leave as is or you’ll be removing the flowers that will open the following summer. The only pruning you should do is in the spring to remove dead wood that has no leaves on it.
Your hydrangea might start to break dormancy inside in the spring. If it’s getting some light, leave it where it is. If you’ve stored it in a dark place, however, bring it into a room with a window.
When you pull the potted hydrangea plants outside after all danger of frost is past, place them first in the shade. After two weeks you can place them in part-sun and enjoy their flowers for another summer.
You say it sounds like too much trouble to bring pots of shrubs inside for the winter? My reply is that we carry lawn furniture inside to protect it, and these long-flowering shrubs bring such pleasure that they are worth some simple actions to enjoy their special flowers.