Oakleaf Hydrangea with discoloured leaves

I apologize if these photos are too large; the last ones I sent were too small so I have a few things to learn.

Today I'm writing with a question another member in my garden club has regarding her Hydrangea quercifolia.

Here is what she tells me:

~ The plant has always exhibited this brown spotted pattern since it was placed in our yard three years ago.

~ I transplanted it to a shadier location in May 0f 2015 but the leaves still exhibit the spotting.

~ That summer (2015), it bloomed profusely but not this year.

~ This year it sent out a "sucker".

~ Our soil is quite sandy but the plant receives water from a buried, irrigation line.
I think the watering is adequate as the leaves are supple and not brittle at their tip ends.

Many thanks if any of you can suggest what is wrong and what she can do about this problem.

 

Could spider mites cause the premature reddening of the leaves?

 

In my experience Hydrangea quercifolia is a pretty tough plant that will stand up to a variety of garden conditions. This looks like it might be a nutrient imbalance, not mites; however, it looks like the plant is otherwise vigorous, so I'd be careful not to make any drastic changes to the soil.

I would ask the following questions:

• How deep is the mulch around the neck of the hydrangea?
  Do the plants around the hydrangea ever show signs of water stress?
• Are other plants around it similarly off colour or undersized?
• What plants/crops have been grown there previously?
• What fertilizers have been used in the area?
• Have herbicides been used?

It looks to me like a nutrient deficiency.

 

Normally redning of plant foliage is the first indicator of a phosphorus deficiency. You could try top dressing the soil around your hydrangea with bone meal, if its not a dificiency the bone meal shouldnt hurt it at all. Good luck!

 

Yes, I immediately thought of phosphorus (P) deficiency, too. However, it is pretty rarely encountered in garden soils locally. Even in very sandy soils, the organic matter present will usually retain P and make it available to plant roots. Cold weather can sometimes trigger localized P deficiency in tissue (exhibited as purple tips in some evergreen species of Viburnum, for example), but this usually clears up quickly with the onset of warmer weather. The reverse (an excess of P in soil) is often true, however, from years of fertilizer (including bone-meal) applications, as P is an element that tends to build up in the soil. (See this article for an interesting discussion on soil phosphorus.) Excessive soil acidity can sometimes cause a deficiency of P in plants, but I would start with a soil test for pH, before any fertilizers or other corrective measures were applied.

 

Actually, what is considered a problem here; the spotted pattern on the leaves as the description seems to suggest, or the "discoloured" leaves as the tittle of the thread seems to suggest?

 

The adjectives 'spotted' and 'discoloured' both are attempts to describe abnormal colouring on the hydrangea leaves. See the photos on the first post.

My friend doesn't think spider mites are the cause but she has been spraying with a Safer product just in case. Of course she wouldn't see an
improvement in this year's leaves. It doesn't look to be a disease problem either.

Other possibilities mentioned by Douglas Justice have also been ruled out . . .

• How deep is the mulch around the neck of the hydrangea? (minimal)
• Do the plants around the hydrangea ever show signs of water stress? (none - irrigation system in place)
• Are other plants around it similarly off colour or undersized? (no)
• What plants/crops have been grown there previously? (the subdivision was developed about 4 years ago)
• What fertilizers have been used in the area? (minimal - dolomite lime on the lawn)
• Have herbicides been used? (none)

A nutrient deficiency does seem to be the most likely explanation. Though a lack of phosphorus causes reddening of leaves it is not usually lacking in our soils as Douglas notes. Still, other causes of phosphorus deficiency Linda Chalker-Scott mentions in her article do not seem to be in play, ie. environmental stresses such as cold temperature, high light intensity, insect damage, and drought. So, perhaps the soil is too acid and/or sandy.

My friend plans to have a proper soil analysis done next spring. I will let you know the results.

Thank you for your thoughts and suggestions.