SEATTLE — One of the most popular shrubs in Northwest gardens is Hydrangea. There are quite a number of varieties to choose from and new incredibly beautiful ones are showing up at nurseries every day
Most of the older Hydrangeas in Northwest gardens are Hydrangea macrophylla or the mop head and lace cap Hydrangeas. These Hydrangeas bloom on growth that occurred last summer. Try to resist the urge to whack your shrub down 2/3rds of the way to the ground. The plant will respond by sending up gazillions of sprouts, and it won't bloom because flowers occur only on growth that occurred last season, exactly what is removed when you cut your hydrangea back hard.
This type of Hydrangea does best when you thin them out by symmetrically cutting about a third of the stems to the ground or to where they connect to another branch near the ground. On the remaining stems, cut the top growth to a healthy bud just below where last year's flowers occurred. You'll get a taller, more elegant looking plant and although you'll get fewer blooms, the ones you get will be bigger and better than ever. This kind of Hydrangeas do best in morning sun or bright shade, and appreciate regular watering in dry weather.
There is, however a newly introduced variety of Hydrangea macrophylla that bloom on new and old wood. Hydrangeas in the ‘Endless Summer Collection’ bloom both on current and older season wood, resulting in a significantly longer blooming season. Mophead varieties offered in the ‘Endless Summer Collection’ are fairly trouble free. While they will still bloom in late summer, they'll bloom earlier and more prolifically if you thin them as recommended for the older style mop heads and lace caps.
Oak leaf Hydrangeas (Hydrangea quercifolia) have leaves that look like the ones on oak trees. These Hydrangeas are native to the Southeastern U.S. and can take more sun than the mop heads can. The white cone shaped flowers fade to pink in the fall. The foliage in fall turn spectacular colors. Prune by thinning out the tallest stems as recommended above.
If you want Hydrangeas that bloom beautifully even if they are cut back practically to the ground. Hydrangea arborescens (smooth Hydrangea) is native to the eastern United States and is hardy to about –30 degrees. Left unpruned, it can reach over 10 feet tall. The most popular variety is ‘Annabelle’ which produces enormous, snow white 12 inch sphere-shaped flowers. The Invincibelle and the new Incrediball series take full-sun and bloom heavily with pink or white flowers.
The other kind of Hydrangea that will bloom in summer, even after being cut back hard in spring, is Hydrangea paniculata (hardy hydrangea). Hailing from Japan and China, these sun-loving Hydrangeas are usually grown as trees, but they can also be cut back practically to the ground if need be. The best-known Hydrangea paniculata is ‘Grandiflora,’ commonly known as ‘PeeGee.’ Hardy to at least –30 degrees, its capable of reaching 15 feet tall and produces gazillions of 8-inch snowball shaped flowers that start snow white before fading to soft pink.
A smaller growing paniculata is ‘Limelight’ which grows only to about 6 feet tall, and features green cone-shaped flowers that turn pink as they age. Although paniculata Hydrangeas will bloom reliably even if you cut them back, only resort to such hard pruning every few years. If you cut back severely on a yearly basis, the stems may become weak and require staking to hold up the flower heads.
Another incredibly attractive dwarf variety of Hydrangea is mountain Hydrangea (Hydrangea serrata) These compact growers are hardier than standard varieties of Hydrangea, and most feature long lasting, attractive lace-cap flowers and colorful foliage. A new favorite of mine is 'Kiyosumi.' The new foliage emerges burgundy gradually turning green infused with reddish purple. The captivating lace-cap type flowers are white, edged in red, before finally fading to rich pink. These hydrangeas can be planted in full sun and still look great even after our mid-July high temperatures.
Finally Hydrangea aspera is a species native across southern China, to Taiwan. It is a large, erect deciduous shrub growing to 10 feet tall and wide, with wide, oval leaves. The flowers are typically borne in large flat heads in late summer, and are in variable shades of pale blue and pink, fringed by white or pale pink sterile florets.
Changing the color of Hydrangea flowers:
You may have heard that you can change the color of Hydrangea flowers by changing the pH (measure of alkalinity) of the soil. It is true that the flowers of some kinds of hydrangeas turn bluer in acid soils and pinker or redder in soils that are more alkaline, but there is more to it.
First of all, it doesn't work on all types of Hydrangeas. Altering soil pH only changes the color of the flowers of Hydrangea macrophylla (bigleaf hydrangea) and Hydrangea serrata (mountain hydrangea). The flowers on hydrangeas species such as H. arborescens (smooth hydrangea), H. paniculata (Panicled hydrangea) and H. quercifolia (oak leaf hydrangea) go through natural color changes as the season progresses, but adding soil amendments to change the pH will have absolutely no effect on the color of the flowers.
Changing the color of big leaf and mountain hydrangea flowers, it isn't entirely dependent on the pH of the soil. Color is actually determined by the amount and availability of aluminum in the soil. In acidic soil with a pH of between 4.5 and 5.5, aluminum is easily absorbed resulting in bluer flowers, while the opposite is true in alkaline soils (pH 6 or above) resulting in pinker flowers. The chemical that is most often used to attain blue Hydrangea flowers is aluminum sulfate (the ingredients in bluing agent) because it adds aluminum while acidifying the soil. Follow the directions carefully. Aluminum is a common element in soil, but it's not a plant nutrient. If you use too much, it could harm your hydrangea. Aluminum sulfate should only be applied to plants that are at least 2 years old. Always water your hydrangea well an hour before treatment. Generally one application per year, applied in March, is sufficient to turn most big leaf and mountain hydrangea flowers brilliant blue.
Due to our acid soils in western Washington, it's easy to turn flowers blue. Turning them pink or red is a slow process that can take a couple of years to work. To achieve rosier flowers, spread 1/2 cup of garden lime per 10 square feet around your hydrangea every spring and fall. Take care to avoid applying lime around rhododendrons, azaleas, camellias or other plants that require acid soil. Feeding with a fertilizer high in phosphorus has also been shown to reduce aluminum uptake, so for redder flowers, feed only with organic fertilizers that contain more phosphorus than nitrogen (2nd number on the bag is higher than the first).
Finally, since there is generally some aluminum in most western Washington soils, especially if you've been using bluing agent around your big leaf or mountain hydrangeas in the past, you might want to give an old time gardener's trick a try. Cut up orange, grapefruit, lemon and lime peels into small pieces and bury them just outside the drip line of your hydrangeas. Citrus peel contains sulfur, magnesium, calcium, and other nutrients that enhance healthy plant growth while increasing acidity in the soil. Do it as often as possible year round and the flowers on your hydrangea should stay sparkling blue. Best of all, think how healthy and buff you'll be after eating all of that extra fruit and vitamin C!
Here are a few of my favorite Hydrangeas.
Hydrangea arborescens 'Invincible Wee White - White flowers
Hydrangea arborescens 'Incrediball Blush' - Pink- big flowers
Hydrangea macrophylla 'Miss Saori' - red or blue small flowers
Hydrangea macrophyyla 'Sol' Red or blue small flowers
Hydrangea macrophylla 'Sabrina''' - sister of 'Miss Saori'
Hydrangea arborescense 'Invincible II; Big pink flowers.
Hydrangea macrophylla 'Wedding Gown' White, flat round flowers
Hydrangea macrophylla 'Let's Dance Diva' - Blue lace cap flowers
Hydrangea macrophylla 'Spike' - beautiful blue
Hydrangea quercifolia 'Little Honey' - golden foliage
Segment Producer Suzie Wiley. Watch New Day Northwest at 11 a.m. weekdays on KING 5 and streaming live on KING5.com. Contact New Day.