Unlocking The Secrets To An Endless Summer

Growing Bigleaf Hydrangeas In Manitoba

By Jim Kohut, Northscaping.com

Since Bailey Nurseries introduced the original 'Endless Summer' hydrangea a number of years back, Manitobans have been discovering the joys of growing bigleaf hydrangeas in our outdoor gardens, plants once reserved for the indoor Easter display. Now with the newly released 'Blushing Bride', a stunning white version of the original shrub, we have a selection of these wonderful plants from which to choose. For all their charm and popularity, however, these varieties remain somewhat of an enigma among Manitoba gardeners. Much of this has to do with the fact that we are unfamiliar with this species and its quirks and eccentricities.

Lovely as they are, the hydrangeas you find at the florists, varieties of the species Hydrangea macrophylla, are not dependable performers in Manitoba gardens. For one thing, they are not reliably hardy; they suffer serious dieback after even mild winters, and they are extremely susceptible to frost. For another, they only bloom on wood of the previous season. If you expect to enjoy any flowers from this species at all, you must have entire branches survive the winter.

'Endless Summer' (now known as 'Endless Summer - The Original') and 'Blushing Bride' are both varieties of the bigleaf hydrangea, sharing almost all preferences and traits in common with the species. They are notoriously sensitive to summer heat, and prefer an even, moderate temperature all day long and across their long growing season. They dislike the baking heat of direct afternoon sunlight, and will quickly wilt. They need consistent moisture at all times, but will rot in standing water. They are not quite hardy in our climate, and they will suffer if we get early fall frosts or late spring frosts.

The big difference between these two varieties and other bigleaf hydrangeas is in the way the flower buds are produced. With the species and most popular varieties, the flowers are only produced on wood of the previous season, typically from buds at or near the terminal ends of the stems. These newer varieties also bloom from the terminal buds, but are unique in that they will also produce flowers on new wood of the current season.

In Manitoba gardens, most of the branches (along with the terminal buds) will usually die back (unless you're prepared to do some serious mulching) and thus not produce flowers. However, the buds along the lower branches and the buds at the base can be expected to produce the magnificent flowers from early or mid-summer on to fall, as long as the plant is otherwise happy.

Care In Siting And Planting

Proper siting of these plants is critical for their success in your garden. The ideal planting location will receive morning sun and afternoon shade. Be careful not to locate them against a lightly-coloured south or west-facing wall, as the reflected sunlight will pretty much bake them. A sheltered location that traps snow in winter and provides protection from brisk winter winds is optimal.

Prepare a special planting site for these plants. While they are relatively tolerant of a wide range of soil types and pHs, they will benefit from a good quality garden soil high in organic matter, which retains moisture while facilitating drainage. The soil pH may not be critical to the growth of the plants, but it does affect the flower colour of Endless Summer. If you want blue flowers, you must make the soil highly acidic, which is best achieved with copious quantities of peat moss, pine needles and the addition of aluminum sulfate. Otherwise, the flowers will be pink.

Dig a hole at least 2' in diameter and 16” deep, excavating the existing soil and replacing it with the amended organic mixture. Make sure that the site is well-drained, as hydrangeas are relatively intolerant of standing water. To conserve moisture, cover the soil surrounding the plants with a summer mulch of pine needles, shredded bark or bark chips.

First Growing Season Care

Any troubles experienced with these plants are usually caused by the fact that most gardeners underestimate the importance of first year care. First and foremost, Manitoba gardeners must have realistic expectations of performance in the first few years; this is a long-lived plant that takes its precious time to get established. Therefore, the primary objective of the first year is to get the plant settled in its new garden home and to encourage the development of a deep and healthy root system. The abundant flowering will then follow in later years.

Proper watering of hydrangeas is critical to their success, and this is even more important in their first year when their roots are still developing. The objective should be to keep the soil consistently moist, while never permitting water to stand for any length of time. Watering 2-3 times per week is ideal, as opposed to one large dousing every week. And let the plants guide you; if you see the leaves starting to droop or the flowers wilting, take it as a sign that you are not watering them frequently enough.

Fertilization is the other area where gardeners often misunderstand the preferences of this species. Contrary to popular belief, bigleaf hydrangeas should be fertilized with a low-nitrogen, high-phosphorus fertilizer. That means you should look for one with a low first number and a high second number, for example a "10-40-10" composition. Too much nitrogen will result in vigorous vegetative growth but little or no flowering, not to mention inadequate root development. Fertilize often in the first year to promote a healthy root system.

However, all fertilizing must cease by the middle of July, as the plants need to begin the process of shutting down their growth for the coming winter. Keep up the regular watering through into fall, and be sure to give the plants a final thorough watering in late fall after they have gone dormant but before the ground freezes.

First Winter Care

All bigleaf hydrangeas are a challenge to overwinter in Manitoba, although these two varieties are somewhat more forgiving. The objective should be to protect the crown and lower buds at all costs, while encouraging as many of the buds along the branches as possible to survive. The best way to protect them is to plant them in an area that gets reliable snow cover. You can also shovel the early snows onto the plants, mounding as high as possible for maximum protection.

Alternatively, you can cover your bigleaf hydrangeas in late fall with leaves, peat moss or flax straw to a depth of at least 6” - the more the better. Be sure to secure the mulch against wind with netting or pine boughs. Timing is crucial; cover them late enough in the season to ensure that the plant has gone fully dormant but before the coldest temperatures hit. This will usually be some time in early November.

It's best not to prune bigleaf hydrangeas at all during the first growing season, and especially not in late fall, as this may allow the winter chill to penetrate deep into the stems. Leave the flower heads on all winter and then prune them off in spring once active growth has resumed.

Bigleaf hydrangeas are notoriously slow to resume growth in spring. Many gardeners erroneously presume a plant to be dead because it hasn't broken bud in May, but that's not unusual for this species. To encourage the plants to get growing, remove both the winter mulch and the summer mulch in mid spring, after all threat of late spring frosts has passed. This will expose the black soil to be heated naturally by the sun. Be sure to replace the summer mulch as soon as the plants resume their growth. You can also start your fertilization regimen at the same time.

Subsequent Behaviour And Care

For those of us not familiar with growing bigleaf hydrangeas in an outdoor garden setting, it's important to understand how these plants will grow over the course of their lives. They are very long-lived once they are established and happy in their growing location, so they are worth all the effort you can give at the start.

Having patience is very much a key to success. There will likely be limited flowering the first few years as the plants develop their roots. Because they are slow to emerge in spring, and because the terminal buds probably won't survive the winters, they will likely not start blooming until July in Manitoba. We will, however, enjoy a prolonged period of bloom from that point to the end of the season, a time in northern gardens when flowering shrubs are in short supply. Gardeners will also love the length of bloom of the individual flowers; they can hold their colour for three weeks or more before beginning to fade!

For the most part, care in subsequent years is similar to the first few years. Keep up a strict regiment of watering and fertilizing to keep the plants happy. It's best not to prune young plants for the first 2-3 years in your garden other than spring pruning to remove the dead flower heads. After this, you can begin to deadhead spent flowers as they fade, which will help to encourage additional flushes of bloom across the season. Always prune to 1/2" above an active and healthy set of buds.

You'll also have to do some maintenance pruning each spring to remove the dead portions of branches. Don't worry about these dead branch tips or even entire dead branches; as long as the basal buds and lower branch buds survive, you should get flowers. Wait to prune in spring until new growth has resumed to see which buds survived and which didn't; looks can be deceiving!

And that's about it. With extra care and a healthy dose of patience, northern gardeners will learn to enjoy the pleasures of the bigleaf hydrangea in their yards that our southern counterparts have enjoyed for centuries!

This article has been adapted from an article on the Northscaping.com website, and is used with permission from the author.