Hydrangeas 101

Man, oh, man do we love hydrangeas. We swoon over their big blowsy flowers, plant them in the dozens, and cuss them out when they don't do what we think they should. I get so many hydrangea questions, that hardly a day goes by without one. So, I teach Hydrangeas 101 as a walk and talk and as a class at The Morton Arboretum so you, fair gardener, can go to the independent garden center, buy them, plant them, and know what to expect.

It is spring, and our fancies turn to pruning as we get outside and soak in the precious sunlight after a long, cold, winter. It's a good time to review the different types of hydrangeas and what the heck to do (or not do) with them when it comes to spring clean up.

Hydrangea arborescens 'Annabelle'

Annabelle Hydrangeas (Hydrangea arborescens)

Notes: This is the classic, old-fashioned hydrangea that everyone knows and loves. It originated from Anna, IL and a chance find by two sisters who propagated it. It was introduced in 1962 to the nursery trade. It is crazy easy to grow and extremely hardy. People will tell you to plant it in full sun - don't do it! You have to water the snot out of it if it's in too much sun and who has time or the money in the budget for that?

Flowers: Blooms in late June, early July. Large rounded mophead flowers that start green, turn white, go back to green, then dry out and become papery. Usually we leave the dried flowers on the plant for winter interest and deadhead them in the spring. Best flowering occurs in part shade. Blooms on new wood.

Habit: Upright, loose and billowy. Stems will slowly colonize.

Fall color: None appreciable.

Bark: Smooth reddish-brown on old stems, green on new.

Size: 4 to 5 feet high and wide, although they will slowly spread. If cut back each spring, they will grow about 3 feet in a season. Once they reach about 5 feet, they don’t get taller.

Sun: Part shade to full shade.

Soil: Average to moist

Pruning: Deadhead in the spring. If you want the plants to be shorter, cut them back to a couple inches of soil level in March. However, you will create younger, weaker stems, so flowers may flop more.

Cultivars: Incrediball – bigger stems, bigger flowers. Incrediball Blush – pale pink flowers. Invincibelle Spirit – pale pink flowers.

Hydrangea macrophylla 'Endless Summer'

Big-leaf Hydrangeas (Hydrangea macrophylla)

Notes: This is the one that confuses everyone. I don't even bother growing it because the performance tends to be so disappointing. It's also the highest maintenance. You see how little that Endless Summer flowers in the picture? And that's a good year. LEAVE THE STEMS UP ALL WINTER. Just because some landscaper or homeowner got it into their heads that they should be cut to the ground every fall, doesn't mean that's the correct way to prune it. Loosen up, people! Also, this is a shade lover. If you want to watch it wilt and enjoy a huge water bill, plant it in full sun. No, don't really. Stick it in half a day of morning sun where it's truly happy.

Flowers: Blooms beginning in June, then through the summer into October. Large mophead or lacecap flowers that change color depending on soil acidity. They will be pink in Illinois soils unless you add an acid fertilizer, then you can turn them lavender or blue.  Add a cupful of fertilizer around the roots in early spring and again in September. Deadhead faded blooms as they tend to shatter once they go papery. Deadheading also promotes new bud formation, although it’s not essential to keep it flowering all summer. Best flowering occurs on old wood, although there are many cultivars that flower on both old and new wood.

Habit: Rounded

Fall color: Reddish-purple

Bark: Dark reddish-brown.

Size: About 3 feet high and wide, growing 2 to 3 feet in a season. These will not get much taller than about 3 feet.

Sun: Part shade to full shade.

Soil: Average to moist

Pruning: Leave stems up all winter for less winter damage and cut the dead bits off when they start budding out in the spring. Cold damage starts at the tips of the stems and works its way down, so the more stem you have, the better chance at living tissue when we come out of winter. This type of hydrangea will have dormant flower buds held on the stems all through winter, so protection from winter wind (our winter winds generally come from the northwest) is commonly recommended. For those cultivars that only bloom on old wood, you may get lots of great foliage, but no flowers because the buds were all winter-killed. For these, consider treating them as you would a hybrid tea rose. When the ground is truly frozen in December, do a mound of mulch around the crown up about a foot. Pull the mulch away in March when we start warming up.

Cultivars: Lots! When looking at this type of hydrangea, you need to think about how it blooms. The Let’s Dance, Bloomstruck, Endless Summer, and Endless Revolution cultivars all bloom on old and new wood. The Cityline and Lemon Daddy cultivars bloom on old wood. 

 Hydrangea paniculata 'Limelight'

 

Hydrangea paniculata 'Pinky Winky'

Panicle Hydrangeas (Hydrangea paniculata)

Notes: This is your most drought tolerant, sun-loving hydrangea. This one goes in full sun. It has smaller leaves and can handle it just fine. Most are large. See that top photo? That's about a seven foot Limelight. The most breeding work has been done to get them smaller and get showier pink shades as the blossoms fade.

Flowers: Blooms in late June, early July. Large conical flowers bloom white, then as petals age, they turn shades of pink to magenta. Flowers then dry, go papery, and hold for winter interest. Usually we leave the dried flowers on the plant for winter interest and deadhead them in the spring. Best flowering occurs in full sun. Blooms on new wood.

Habit: Upright, loose vase shape. Also trained as a tree.

Fall color: Yellow, although Quick Fire turns orange.

Bark: Pale grey

Size: 6 to 8 feet high 5 to 6 feet wide, but there are many shorter cultivars. The large varieties grow about a foot a year. The dwarf cultivars will do between 3 and 6 inches.

Sun: Full sun to part shade.

Soil: Average to well-drained soils.

Pruning: Deadhead dry flowers in spring. To control size, you can prune them in late winter. However, with the explosion of different cultivars, you can typically find one that will get the size you want.

Cultivars: Lots! Vanilla Strawberry, Pinky Winky, Limelight, and Quick Fire all get large. Little Lime, Firelight, Magical Flame, Strawberry Sundae are medium sized. Bobo is the shortest of the bunch at 3 to 4 feet.

Hydrangea quercifolia

Oakleaf Hydrangea (Hydrangea quercifolia)

Notes: Protect this one from bunnies in winter. Just cage it. Trust me. It's one of those bunny candy plants. When left alone, it matures into a stunning layered creature of endless delight. The fall color on these is not to be believed!

Flowers: Blooms in late June, early July.  Huge conical flowers that bloom white and then as petals age, turn rose to magenta before drying out and becoming papery. Usually we leave the dried flowers on the plant for winter interest and deadhead them in the spring. Blooms on old wood.

Habit: Loosely rounded.

Fall color: Reddish-purple. Outstanding!

Bark: Reddish-brown and peeling.

Size: 6 to 8 feet, although there are shorter cultivars. Grows about 6 inches a year.

Sun: Part shade

Soil: Average to well-drained soils.

Pruning: Only if you have to. Because it blooms on old wood and grows slowly, we don’t usually prune oakleaf hydrangeas unless absolutely necessary. Protect this one from rabbits over the winter, as they like to nibble the stems when the shrubs are small.

Cultivars: Many! Ruby Slippers stays about 4 to 5 feet and the petals age to a rich magenta. Alice is a classic large variety. Gatsby Star has double flowers. There are more available.

 

Hydrangea serrata 'Tuff Stuff' (image courtesy of Proven Winners)

Mountain Hydrangea (Hydrangea serrata)

Notes: The newest kid on the hydrangea block, this one has big potential to give you flowers all summer without the hardiness issues of H. macrophylla. I'm the type of plant geek that checks on specimens each year at our public gardens to see how they do. I've been impressed with the Tuff Stuff series as a reliable performer in more open sites. I'm going to continue to monitor it at The Morton Arboretum because a). I'm there all the time. and b). They've planted a lot of it in different areas.

Flowers: Large lacecap flowers beginning in June and blooming into October. These also change color from pink to blue, depending on soil acidity. Deadhead faded blooms as they tend to shatter once they go papery. Deadheading also promotes new bud formation, although it’s not essential to keep it flowering all summer. Blooms on old and new wood.

Habit: Rounded

Fall color: Burgundy

Bark: Dark reddish-brown.

Size: 2 to 3 feet

Sun: Part shade to full shade.

Soil: Average to well-drained soils.

Pruning: Leave stems up all winter for less winter damage and cut the dead bits off when they start budding out in the spring. This type of hydrangea will have dormant flower buds held on the stems all through winter, so protection from winter wind (our winter winds generally come from the northwest) is commonly recommended. This type is the newest hydrangea on the market and is supposed to be hardier than H. macrophylla.

Cultivars: Tuff Stuff – blossoms can change color and is 2 to 3 feet. Tiny Tuff Stuff – blossoms can change color and is just 2 feet. Tuff Stuff Red – blossoms stay a bright cherry pink and is 2 to 3 feet.

(image courtesy of Andrea_44) 

Climbing Hydrangea (Hydrangea anomala ssp. petiolaris and Schizophragma hydrangeoides)

Notes: When allowed, this vine can get huge and eat your house. However, few vines bloom in shade and these do year after year. Prune it to shape it, but let it be its exuberant self and you'll love it for years and years. The bark is truly awesome. Just put it on a very sturdy trellis or let it climb on a wall. It has clinging rootlets, so it will scramble anywhere it can get purchase.  

Flowers: Large white lacecap flowers bloom in July before drying out and becoming papery. Usually we leave the dried flowers on the plant for winter interest and deadhead them in the spring. Blooms on old wood.

Habit: Slow growing climbing vine

Fall color: None

Bark: Reddish-brown and peeling.

Size: around 30 feet, although can be kept smaller with pruning

Sun: part shade to full shade

Soil: Average to well-drained soils.

Pruning: Only to train it. Because it blooms on old wood and grows slowly, we don’t usually prune climbing hydrangeas very much unless they wander off where they aren’t wanted.

Cultivars: Miranda is a yellow variegated leaf. Rosea is a pink flowered Schizophragma hydrangeoides.