Hydrangea

(Question)

We have a south facing garden in Toronto.  At the most south part of the garden there is a Lilac tree, a Rose bush and some large Hosta.  There is also a large tree that provides shade at the south end after the morning sun.  I planted a hydrangea in an area near the lilac.  It was doing OK but now is droopy and wilting.  It gets morning sun but not really any afternoon sun.  Should I move it to where it gets more sun?

(Answer)

Wilting in a plant can be the result of several different causes, but the immediate cause is usually dehydration.  The key is to identify what is causing the water deficiency, and then rectify it.  The light exposure your plant is currently receiving should be fine.

Is your hydrangea receiving enough water?  Hydrangeas are thirsty plants so require frequent watering.  Check the soil around your plant, push the mulch aside and stick your finger about two inches into the soil.  If it is bone dry, then water deeply.  Try to establish a schedule of deep watering that allows for the soil to dry out slightly in between.  New plants will require more watering as their root systems may have transplant shock and they have yet to establish themselves in their new soil home.  If you have not mulched around the plant, I would advise doing so as this will help retain moisture in the soil.

Or is it receiving too much water?  If the soil around a plant has too much water and becomes waterlogged, the plant will drown because the spaces between the soil particles are filled and it cannot take up any oxygen.  Plant roots need enough air in the soil to breathe.  If it is sopping wet, then leave it alone to dry out.  A hydrangea that is standing in water will become stressed and susceptible to root rot.

Both of the above can cause dehydration of the plant.

If the soil around your hydrangea is moist, or if your plant does not recover from the wilt even after watering correctly, then the culprit may be injury to the root system, either mechanically or biologically.

By mechanical injury we mean that the hydrangea may have been injured during the transplant process which can cause severe shock and stress.

Biologically, hydrangea roots that are drought-stressed can become vulnerable to injury by several kinds of fungi, resulting in root rot.  One of them is the Armillaria mellea or Armillaria tabescens fungi, which cause the leaves and the wood to turn brown and, ultimately, death of the plant.  There is no cure for armillaria root rot.  Another possible fungus is Phytophthora nicotiana, which, in addition to wilting, will cause yellow foliage and stunted growth.  Again, there is no cure for phytophthora root rot.

If your hydrangea does have root rot, then be very thorough when you remove and clean up after the death of the plant.  These fungi persist in the soil and planting materials for a long time and cannot really be eradicated.  Throw all diseased plant material and mulch away, do not compost them or move them to another area in your garden.  Sanitize any tools you use.  Do not plant another hydrangea in the same place.