Hydrangea How-To: Part 1

Hydrangeas are plants that seem to come in and out of fashion in these parts. Down South, they are used fairly consistently in the home landscape. Perhaps they haven't been used as frequently in our region because our choices of most cultivars and varieties are somewhat limited when one shops locally. Here is an instance where mail order definitely broadens the choice of what we can use.

How I envy those folks who only live a few hours drive south of our region! They can grow the macrophyllas and they can count on a yearly show. In our region, they bloom more consistently in that rim of areas around the lakes that have a zone 6a rating. Those of us in zone 5b might see a fairly regular show, and then again, we might not. We might have to be a bit disappointed every three or so years when our winters get a bit harsh, or if cold temperatures return after the initial spring warm-up. Folks living in zone 5a have an even tougher time growing the macrophyllas.

The H. macrophylla cultivars include those that one can alter the color of the flowers by adding a soil acidifier or sweetener. In some of the catalogs, these plants are referred to as pH indicators. While that is a term used somewhat loosely, it is true that some of the macrophyllas will give a general indication of the relative acidity or alkalinity of soil by their color. However, not all of these hydrangeas will alter in color dramatically, if at all.

H. macrophylla comes in two main forms. The Hortensias, or "mopheads", are the forms we see that have the rounded flower heads that resemble a ball of flowers. The Normalis, or "lacecaps", are those flattened heads with large outer flowers, the male flowers on the outer edges, and with the tiny inner, or fertile flowers.

Three of the hardier mopheads include 'Nikko Blue', with rounded flower heads that tend towards the color blue. In more alkaline soils, 'Nikko Blue' will be more pinkish in hue. In more acidic soil, it will be more to the true blue in color. 'Glowing Embers' is a pink form. It is called "red" in many catalogs, but it is actually a deep pink. It is very difficult to change to blue, and will always retain most of its pink coloration. 'All Summer Beauty' is a mophead that tends to be blue, but can be changed to a more pinkish tone, which will most likely be the case in most of our area if we do not acidify the soil.

JUST IN! An exciting new introduction of H. macrophylla is 'Endless Summer', a mophead or hortensia for more northerly gardens. I have read several favorable reports, including from Monrovia Nurseries and Gardens Of The North Nursery. What's all the fuss about? Well, this is one plant that really delivers in the more northern or border areas for the macrophyllas. Unlike its brethren, this blooms on both old AND new wood! This means that even with winter die-back, this hydrangea, which is root-hardy in our area, will send up new buds on current year growth! 'Endless Summer' changes the rules about successfully growing H. macrophylla. The bushes respond well to pH alteration, so it is possible to change the color of flowerets from pink to blue or vice-versa. It grows about 3 to 5 feet tall with a similar spread. Removing spent blooms encourages rebloom as well. According to the information from Monrovia, if the new growth is removed by 1/2 in the spring, more blooms will result. 'Endless Summer' will bloom from April or May right up to frost in our region. Like most other hydrangeas, morning sun is welcome, but afternoon or dappled shade is best for this plant. It appreciates a humus-rich, well-drained yet moisture-retentive soil.

The lacecaps are hardier in this region. They are fully hardy into zone 6, but some of them show more vigor and hardiness into zone 5 than the mopheads. 'Blue Wave' is a lacecap that has blue flowers, or the tendency to be blue. In our region, alkalinity is generally the norm, and this is one plant that will tend to take on more pinkish tones unless grown in an acidic soil. 'Pink Lacecap' is the counterpart of 'Blue Wave', and as its name implies, has more definite pink flowers. It is also one of the hardier lacecaps. 'Lemon Wave' has variegated leaves, green and yellow, with blue flowers. Any branches that display solid green foliage need to be removed, as the plant might tend to revert.

If you are growing one of the macrophyllas that can have its color altered by adjusting the pH of the soil, be very cautious about what you use to alter the acidity or sweeten the soil. Try to use a non-aluminum sulfate acidifier to alter acidity. Most of the soils in our region are alkaline already, but if you need to sweeten the soil, use lime or wood ashes to increase alkalinity. Also add copious amounts of organic material and compost to the growing site. Hydrangeas of all types need to grow in soils high in organic material. If your soil is heavy clay or sandy without an abundance of organic material, the lime or acidifier can harm the soil and the plants growing in it. Avoid aluminum sulfate to acidify the soil as it leaves heavy metal traces. I personally use sulfur to acidify my soil.

It often takes a long time to see the effects of what you have used to alter the color of the hydrangeas. If you alter the soil pH in the spring, it may take up to four months for the effects to show up in the flowers. Fall application will show the effects the following growing season. Even then, be aware that it is not unusual for a plant to sport different colors at the same time while it is responding to the change in pH. Above all else, please follow the recommended rates for using these products. Also be sure to apply at the correct application intervals! If you think that if a little is good so a lot must be better, think again! These hydrangeas will not respond any more quickly by more intense dosing of these agents. These products can harm the plants if used incorrectly.

Just a footnote on the subject of pH: Another thing I have been hearing about is to use coffee grounds and pine needles to make soil more acidic. I do not know if this will work, but I have heard from several gardeners who swear by it. I intend to try this with my 'Nikko Blue' hydrangea, as I refuse to use aluminum sulfate in my garden.

When pruning any of the macrophyllas, be aware that they are plants that bloom on old wood. Any growth this year will produce the buds for next year's flowers. This is why they are so iffy in our region. They sometimes fail to bloom if their buds are killed by the cold. You want to give them every chance to perform, so don't stack the deck against them by improper pruning. Try not to prune them at all, but if you do, prune them no later than the middle of July. Don't prune them any other time of year.

Because of our variable climate, plant the macrophyllas in a protected spot. Don't let them dry out and provide some afternoon shade. They appreciate dappled shade, so keep that in mind. Some people wrap their macrophyllas in late fall to protect the buds, but I don't. My 'Nikko Blue' is in a protected spot, and in truth, does get hit by cold some years. However, more often than not, I do get a good flower show consistently because it is in a protected area.