Gardeners in USDA zones 3 to 5 often find it challenging to grow hydrangeas that bloom. The harsh, freezing winters of the northern zones can damage and kill the forming flower buds of older varieties. This is because the traditional hydrangea plant only forms flower buds for the following year on the old wood of the plant. Fortunately, newer 'everblooming' varieties, like Endless Summer, have been developed to produce new buds on both old wood and new wood. If you garden in a northern zone and have an older hydrangea variety or experience winter temperatures that are below 5 degrees F for any length of time, you will need to winterize and protect your hydrangea to have it bloom the next summer.
Preparing Your Hydrangea for Winter
Discontinue fertilizing your hydrangea at the end of August so the plant will stop producing blossoms and begin preparing itself for winter dormancy. When the first frost of fall arrives, it is time to protect your hydrangea from the winter freeze.
Push four to six wooden stakes into the ground around your garden hydrangea. The stakes should be 10 inches higher than the height of your hydrangea. You may need to trim the branches at the base of your hydrangea.
Wrap chicken wire around the wooden stakes to surround your hydrangea. You can secure the ends where they meet by either bending the wire ends of one side to create hooks, that will latch onto the other side, or tie the seam together with plastic ties.
Work your organic material, like leaves or pine straw, carefully down and around your hydrangea within your stake and chicken wire frame. The organic material will act like insulation during the winter, protecting your hydrangea from the freezing cold. As you stuff the frame with leaves and/or pine straw be very careful not to break or damage any of your hydrangea stems and branches.
Check your protected hydrangea several times throughout the winter to make sure the organic material has not compressed and exposed your hydrangea. If that happens, simply add more organic material to the frame.
For areas where winter has alternating periods of snow melt and freezing weather, you may want to add a 'lid' of plastic foam or wood to the top of your frame. This will keep the water from seeping through the insulating organic material onto your hydrangea branches and then freezing when the temperature drops. Freezing ice on your hydrangea may damage or destroy the developing buds.
Your Hydrangea for Summer Blooming
Carefully uncover your hydrangea in the spring when the threat of frost has past. You will see that your hydrangea has started to leaf out by then. Be very careful when you remove the organic material from around the stems and branches of your hydrangea so you do not damage the ends of the stems or branches. Damaged branches and stem ends may destroy the hydrangea buds that you so carefully protected over the winter.
Remove the chicken wire frame from around your hydrangea.
Water your hydrangea once a week, deeply, throughout the spring and summer growing season. Although hydrangeas do not like soggy soil, they appreciate growing in a moist soil.
Apply a balanced, time-released fertilizer, like 10-10-10, in the spring, then two more times during the summer. Discontinue any fertilizer application in late August, so your hydrangea can begin the process of dormancy.