By Eleanor Moyer, Clay County Master Gardener Volunteer

I’ve been fortunate to move to a much smaller house recently with a garden ready to

enjoy. The previous owners placed 5 beautifully coiffured mop head Hydrangeas where

they can be enjoyed from the screen porch. So far, so good. On closer inspection I can

see round black dots on the leaves of each shrub which got me searching for

hydrangea help!

Now that October is here, many gardeners want to tidy up the landscape—in the case

of Hydrangea macrophylla (French, Big Leaf, Mophead) this is the absolute wrong thing

to do. These plants are setting flower and leaf buds for next year’s show. If you cut

them back, you cut away the beautiful flowers for next spring. Even if you have

varieties like Endless Summer which bloom on new and old wood, you will prevent the

large spring blooms which develop on old wood and be left with the smaller blooms later

in the summer. But no fear, there are some other tasks that will make next year’s show

more bountiful.

It has been particularly dry. Check the soil down at least two inches. If the soil is dry,

water deeply at the base in the morning. Avoid overhead watering. Hydrangeas need 1

inch of water per week-that’s about 5 gallons. These mopheads tend to wilt in the

afternoon sun, but they may not need water—check the soil first. The roots are shallow

so putting at least 2 to 3 inches of mulch and/or compost will help preserve moisture

and protect against winter weather. Be sure not to pile mulch around the center (crown)

of the plant.

They do not need fertilizer especially any nitrogen. Be careful if you feed lawns near

the plants as hydrangea roots reach past the drip line. If anything potassium (Muriate of

Potash) is beneficial for most shrubs and perennials in the fall. In fact the Royal

Horticulture Society has promoted this application for decades. Naturally a soil test is

the most scientific way to measure.

This is the perfect time to treat your blossoms for color. It takes a while for the soil to

sweeten (flowers turn pink) or become more acidic (flowers turn blue). For blue flowers

the soil must have a pH level less than 5.5. Again, a soil test will determine this level. If

you already have hydrangeas, then the color of your bloom will tell you the acidity of the

soil. If you want the pink blooms to turn blue, then add elemental sulfur. If you want

your blue flowers to turn pink, add agricultural lime. These minerals are readily

available in stores and on line. Just follow the recommended dosages on the labels.

So what about my black spots? These are usually caused by fungal diseases like

Cercospora or Anthracnose. It has been dry, but also humid and overhead watering

may have contributed. The good news is that this will rarely kill a plant, but I know you

want yours to look unblemished, as do I. First clear away all fallen leaves. Dispose of

them in a burn pile or trash. In early spring apply neem oil, a copper-based fungicide or

a preventative treatment like chlorothalonil. If your leaves look scorched around the

edges, the plant probably needs to be watered and mulched. Let’s hope all this will lead

to Hydrangea heaven!