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There are few northern gardeners who haven’t at least once wished that they could grow the lovely florist’s hydrangeas in their gardens, the kind with the enormous globular mopheads of pink, blue, or white flowers that are on display for Easter, or that accent the most delightful dried flower arrangements.
We have come a long way with the introduction of the highly popular Annabelle hydrangea, which has brought the white-flowered form into even the coldest northern gardens.
But alas, the wonderful pink and blue bigleaf varieties have remained elusive as ever.
Lovely as they are, the hydrangeas you find at the florists, varieties of the species Hydrangea macrophylla, are not dependable performers in our northern climate, to say the least.
For one thing, the plants are not reliably hardy; they suffer serious dieback after even mild winters, and they are extremely susceptible to frost. Compounding this, they only bloom on the wood of the previous season.
If you expect to enjoy any flowers from this species at all, you must have entire branches, and particularly the terminal buds, survive the winter, and that’s a tall order (pun intended). Simply put, these are not plants for northern gardens.
At least this was the case until a few short years ago.
The plant developers at Bailey Nurseries in the Twin Cities discovered a variety of bigleaf hydrangea that was defying the odds, growing well and blooming wonderfully in a St. Paul neighborhood, in full defiance of the harsh zone 4 winters.
Thus began the story of Endless Summer, the wonderful new introduction that has taken the northern gardening world by storm.
For all its charm and popularity, Endless Summer is somewhat of an enigma among gardeners in the colder zones 3 and 4. Much of this has to do with the fact that northern gardeners are unfamiliar with this species and its quirks and eccentricities.
We have received numerous requests for advice and information on how to plant, grow and care for this unique variety, to consistently deliver the wonderful flowering performance that the species is renowned for.
We aim to please, so without further ado, here are some tips for optimizing the performance of the Endless Summer hydrangea.
Getting To Know Your Endless Summer
The key to understanding Endless Summer is to understand the species itself. As a variety of bigleaf hydrangea, it shares almost all preferences and traits in common.
The flower color is a good example of this. When the plant is grown in acidic soil, the flowers will be a pastel blue or soft bluish-pink combination, while they will be rich pink when grown in more neutral or alkaline soils. This is as true for Endless Summer as for the species itself.
Bigleaf hydrangeas are notoriously sensitive to summer heat, and really like an even, moderate temperature all day long and across their lengthy growing season.
They abhor 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 less than optimally hardy for the northern climate, and they will suffer immensely from early fall frosts and late spring frosts. In these regards, Endless Summer is quite similar to the species and the other popular cultivars of southern gardens.
The big difference is in the way the flower buds are produced. With the species and all prior varieties, flowers are only produced on the wood of the previous season, typically from buds at or near the terminal ends of the stems.
Endless Summer also blooms on these terminal buds but is unique in that it will produce flowers on new wood of the current season as well.
This is actually a bit of a misnomer, from my experience. The truth is that Endless Summer blooms on the buds at the ends of the branches, as well as from buds anywhere along the branches and near the crown, known as basal buds.
It will also produce flowers on genuinely new buds that are formed in the current season, but our growing seasons in the North are generally too short to enjoy this benefit, save perhaps one flush late in the season.
In practice, northerners can expect the terminal buds to die back (unless you’re prepared to do some serious mulching!) and thus not produce flowers, but can expect the buds along the lower branches and the basal buds to produce flowers, followed by possibly one flush of flowers from new growth.
The result is magnificent; continuous flowers from early or mid-summer on to fall, as long as the plant is otherwise happy. And for this plant, the key to happiness lies in proper planting and ongoing care.
Care In Siting And Planting
The proper siting of Endless Summer is critical to its success in the landscape. From a design perspective, depending on the degree of dieback it will experience in your particular location, you can expect the mature height and spread to be somewhere in the range of 2-4’.
This makes it ideal for the average garden, and excellent for use in a foundation planting up against a house or along a fence.
The ideal planting location will receive morning sun and afternoon shade, as all bigleaf hydrangeas dislike the direct rays of the hot afternoon sun.
Take precautions to avoid locating them against a light-colored south or west-facing wall; the reflected sunlight will further exacerbate the problem. A sheltered location is ideal, one that traps snow in winter and provides protection from brisk winter winds.
Plan to prepare a special planting site for these special plants. While they are relatively tolerant of a wide range of soil types and pHs, they will benefit from 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 color.
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.
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 or straw.
First Growing Season Care
Any troubles experienced with Endless Summer are usually caused by the fact that most gardeners don’t appreciate the importance of the first year care of for these wonderful plants.
Above all, gardeners must have realistic expectations of performance in the first few years; this is a long-lived plant that takes 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 subsequent years.
Proper watering of hydrangeas is critical to their success, and this is doubly so in their first year when their roots are very much underdeveloped. The objective should be to keep the soil consistently moist, while never permitting water to stand undrained.
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 with enough frequency.
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 the establishment of a healthy root system.
However, all fertilizing must cease by the end of July at the latest. The plants need to begin the process of shutting down their growth for the coming winter and fertilizing any later than this will encourage them to keep growing.
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, although Endless Summer is somewhat more forgiving. The objective should be to protect the crown and basal buds at all costs while encouraging as many of the buds along the branches as possible to survive.
If you live in an area that receives reliable snow cover, this may be enough to protect the plants over the winter. You would be advised to shovel the early snow onto the plants, mounding as high as possible for maximum protection.
If snow is unreliable in your area, or you live in a Chinook region with dramatic temperature swings and infrequent snow cover, you will want to mound your Endless Summers in late fall with an organic mulch.
Cover them with leaves, peat moss, or straw to a depth of at least 6” – the more the better, and be sure to secure the mulch against the wind with netting or pine boughs.
Timing is crucial here; cover them late enough in the season to ensure that the plant has gone fully dormant but before the coldest temperatures hit. For most of us, this will be sometime in November.
It’s best not to prune Endless Summer 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 typically slow to resume growth in spring, and Endless Summer is no exception.
Many a northern gardener has presumed 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 into gear, remove both the winter mulch and the summer mulch in mid-spring, after all, the 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 Behavior And Care
For those of us (i.e. most 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.
But they are also characteristically slow to get going, so the gardener’s patience is very much a key to success. There will likely be limited flowering in the first few years as the plants set their roots.
This can often be a cause for concern among novice gardeners; after all, they were in glorious bloom when they were first brought home from the garden center! In truth, they were likely forced into bloom ahead of their time and under optimal indoor conditions, and it will be some time yet in your yard before they can repeat this performance!
Because they are slow to emerge in spring, and because the terminal buds probably won’t survive the winters, Endless Summer will likely not commence the season’s bloom until June or even July in northern gardens.
Gardeners will, however, enjoy the repeat blooming 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 color 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 regimen 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, except for spring pruning to remove the dead flower heads. After this, you can begin to deadhead spent flowers, 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’ll get flowers.
Wait to prune in spring until new growth has resumed seeing 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!