At the Master Gardeners State Conference held in Springfield, Illinois a few years back, I attended a session given by Glenn Herold of Illinois Central College related to hydrangeas. It was very interesting and I've referred to the notes from that session several times. I've also noted that along with clematis, hydrangeas seem to generate a lot of questions. These questions range from when to prune to why isn't my blue hydrangea blue or why doesn't my hydrangea bloom? Like clematis, the answer to most of these questions depends on the type hydrangea you have planted.

The most important thing to know about the hydrangea before you purchase is:

1. Are they hardy?
2. Do they bloom on old wood or new?
3. What color is the flower supposed to be?
4. How much light does this type of hydrangea require?

The following is a guide that you can use when you purchase your hydrangea or perhaps it will answer some questions about any problems you are having with your current hydrangeas.

Hydrangea anomala petiolaris (Climbing Hydrangea) attaches by means of holdfasts to rough surfaces and will tolerant shade well. The bark has a winter interest and the flowers originate from old wood so do NOT prune in early spring. You can prune right after it blooms. This hydrangea is slow to get established – perhaps 5 years, but it adapts well.

Hydrangea arborescens (Smooth Hydrangea) is native to much of Illinois. It will grow 3 to 5 feet tall and equally as wide. This hydrangea has white flowers on new growth so you can cut back all the old wood in early spring. It grows best in part shade with morning sun. 'Annabelle' is probably the best known with large showy mophead flowers. Did you know it is named after Anna, Illinois? It has strong stalks to hold up the flowers. 'Grandiflora' is a mophead but not as compact as 'Annabelle', 'Dardom' is a lacecap flower head while 'Hayes Starburst' has double sterile flowers.

Hydrangea heteromalla is a huge plant as can grow to 18 feet tall. It likes full sun to part shade and has lacecap flowers on the previous season's growth (old wood) so do NOT prune in the spring. 'Breitschneideri' is an improved cultivar.

Hydrangea macrophylla (Bigleaf Hydrangea) is basically meant to be grown in Zone 6 or 7 (we are Zone 5) and it blooms on old wood so this means the old wood part of the plant dies back in our climate so you might have greenery (the new wood) the next year but no blooms. I have one of these. It was given to me as a plant from the florist and I planted not knowing the type hydrangea. It is in a fairly sheltered area but I still only get greenery each year. One year I got ONE bloom and rather than the huge blue mophead type flower on the original plant, I had a pink lacecap bloom.

So this brings us to the color you buy and the color you get. The more acid your soil the bluer your blooms. The more alkaline the soil the pinker your blooms. So if the blue plant you purchased isn't blue, you need to add acid. Unfortunately, I've never been successful to getting the acid content high enough for the color to really be a true blue.

However, some new cultivars have been satisfactory in Central Illinois such as 'Endless Summer' which is remontant – meaning will bloom on both new and old wood (prune only after you see what is going to bloom in spring)

Hydrangea paniculata (Panicled Hydrangea) is well adapted to our area and doesn't like too much water. Most plants grow to 10 to 15 feet tall and are best planted in the sun but will tolerate partial sun. This plant has very hardy flowers on new growth but don't prune -just remove the old flowers in early spring. It is the last of the hydrangeas to bloom – August. 'Limelight' (larger flower clusters that are lime green as new flowers - mophead), ' Little Lamb' is a shorter version of Limelight and I've found I have to support my branches or they lie on the ground, 'Pinky Winky' (pink and white on the same panicle), 'Unique' is a large plant with large lacecap flower clusters and was one of the teacher's choices.

Hydrangea quercifolia (Oakleaf Hydrangea) will grow in any light condition as long as it gets enough moisture. Produces on old wood so prune only after it flowers. It has an exfoliating bark and a lovely fall color – but that color is best if the plant is grown in the sun. It grows 8 to 10 feet tall. 'Brido' is a lacecap with large double flowers, 'Harmony' is a mophead with mostly sterile flowers, ' Pee Wee' only grows 3 to 4 feet and the flowers tend to lay down, 'Flemygea' (Snow Queen) has flower clusters held upright and is 6 to 8 feet tall and 6 feet wide but the teacher considered the best of the Oakleaf Hydrangeas.

Hydrangea serrata is similar to H.macrophylla but has a slightly better cold tolerance and sometimes has good fall color. The leaves may have a red tint in the summer. It, too, blooms on the old wood so might die back and not return in our zone.

Other suggestions were to mulch with pine mulch considered the best for this plant. Fertilizers can be used but instructions should be followed but divide by 2. In other words, one-half the strength indicated on the instructions.

Hopefully, this information will prove a helpful guide for the care of your present hydrangeas or help you make the right selection for new plants.

If you have any horticulture questions, call the U of I Extension office 345-7034. Volunteer

Master Gardeners are in the office on Monday and Thursday from 2 to 4 p.m. to answer your questions.

This column is based on information and materials at the University of Illinois Extension office, located at 707 Windsor Road, Suite A., Charleston, 61920; phone 345-7034; or web site: www.extension.uiuc.edu/coles/