If you have thumbed through catalogs or walked through garden centers, you probably noticed the varieties of hydrangeas on the market.
If you are up on your hydrangea lore, you may be hesitant to purchase these shrubs if you live in a USDA zone 5 and/or have alkaline soil.
Hydrangeas come in white, red, pink and blue. These shrubs are stars in the garden. They cover themselves with large umbel- or pyramidal-shaped blossoms.
Hydrangea arborescens ‘Annabelle’
H. arborescens ‘Annabelle’ is common in our area. It blooms white and the huge (soup-bowl-sized) white umbels turn a muted lime green as they age in late summer. In the fall the blossoms turn tan and last into the winter.
Until recently, ‘Annabelle’ was one of the few hydrangeas that thrived in our alkaline soils.
Hydrangeas have a couple of drawbacks in our USDA Zone 5 climates.
Color in alkaline soil
Let’s discuss color first. The white varieties are stable and what you see is what you get. The reds, pinks and blues are driven by the pH -- alkalinity or acidity of the soil. Buy a blue hydrangea and place it in alkaline soil and you’ll notice the color begins to change. In a year the plant will be producing blossoms in the pink to red range of color, depending upon its color genetics. Plant a pink or red hydrangea in acid soil and it will turn towards the blue spectrum. There is an exception to this that I will discuss later.
Since the blue hydrangeas require a special fertilization program in alkaline soil to keep them blue, I often wonder if people, who have acid soil, long for the pinks.
Hardiness
The second problem with hydrangeas comes from their hardiness.
H. arborescens ‘Annabelle’ is hardy to USDA Zone 4. This is why she has survived in this area for so long.
H. arborescens ‘Invincible Spirit’ is a new member of this group and is touted to be hardy even in the far north. It blooms in shades of pink.
Many other hydrangeas on the market may claim hardiness to USDA Zone 4 but are in fact only hardy to USDA 6. While their root systems are hardy, their stems aren’t. If a hydrangea blooms only on old wood this will keep it from blooming in our cold climate.
Hydrangea aborescens
H. aborescens, known as smooth hydrangea, can be pruned to 6-inches from the ground in late winter. (This is a hardiness clue.)
Hydrangea macropyhlla
Hydrangea macropyhlla, many of the mopheads and lacecaps are in this category, bloom on the old wood and are unreliable here unless covered and protected yearly. The exception to this rule could be H. macrophylla ‘Endless Summer’. One catalog description said it would bloom all the way through Minnesota (a minus -25° to -35°F.) This is a new plant many of my gardening friends are including in their ‘must-haves’. It is interesting that this plant is always pictured as a pink variety in the catalogs but when I purchased one at a local ‘box’ store it was showing white and blue flowers.
Hydrangea paniculata
H. paniculata includes the variety ‘Limelight’. Hardy to USDA Zone 3, it may survive here as well.
Hydrangea quercifolia
H. quercifolia has oak-like leaves. Instructions say to not prune until August, making this plant less likely to perform here.
Hydrangea involucrata
H. involucrata produces flowers on new wood and is hardy to zone 5. ‘Blue Bunny’, hybridized in the Netherlands, should produce blue flowers every year and is not affected by soil pH. I have added this one to my collection and will give you an update in a couple of years. This is the ‘blue’ exception I mentioned above.
Site location
Some varieties of hydrangea require more shade than some others, so do your homework before placing them in your garden.
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