Hello! I'm so confused... I've got two hydrangeas planted in the same area, which for all intents and purposes should be exactly the same (same Mop head variety, same soil condition, etc)





The one on the left has been doing pretty decent, while the other's leaves have turned scorched purple with lower overall growth and fewer blooms. Any suggestions as to what could be going on here?

After noticing this happening a couple of years ago I've tried a number of things like supplementing the right one with a balanced chemical fertilizer, superphosphate, and iron. I've also tried anti-fungal sprays, but to no avail.

(BTW, it's just getting to be winter here in New Zealand, so what's pictured here is them pretty much done for the season, expecting them to drop all their leaves soon as usual)

Looks like the one on the right got hit by an early frost or is a variety that normally changes the foliage this way in the Fall. You candecide which by analyzing the weather data for the night when the change happened. The left one is either simply more prepared for cold, is a variety that does not change leaf foliage colors much in the Fall or did not get hit with early frost. Frost can be spotty when overnight temperatures are around 6°C. One plant gets hit and the other ones is missed. Or one side of the plant gets hit and the rest is ok. Color change in the leaves can also something normal for some varieties in the Fall. Think: oakleaf hydrangeas; their leaves should be gorgeous in the Fall. But most mopheads will simply turn the leaves brown though.

Fertilizer - the latest application of a fertilizer should be made three months before your average date of early frost. So for example, if your average date of early frost falls around May 16 then your last application should be done on February 16. If the soil has no nutrient deficiencies, consider fertilizing when necessary. You can stop fertilizing after the plant is established as long as you always maintain 7-10 cms of organic mulch; hydrangeas are not heavy feeders like roses are so they will then feed off the decomposing mulch. Or just fertilize once in Spring.

Superphoshate - not normally needed unless the soil has nutrient deficiencies (for example: growing in sandy soil)

Iron - only needed when growing in alkaline soils. Amend only per product label instructions because some products contain sulfur and too much sulfur can injure the hydrangeas shallow, tiny and fibrous roots (they only grow about 10 cms deep). You can also use garden sulfur, greensand, iron-chelated liquid compounds or iron sulfate. The liquid compounds will more quickly restore back the dark green foliage when the plant leaves develop iron chlorosis but the liquids need to be applied more often than the granular products. If trying to produce blue blooms, iron may help when the soil already has sufficient amounts of aluminum. If not, consider using aluminum sulfate per label directions (but keep a/s away from azaleas and rhododendrons). If you apply too much fertilizer or apply it too late or early, that keeps the plant in "grow mode" and makes it susceptible to frost damage in the Fall or, if you fertilize as soon as the plant breaks dormancy too early, fertilizing could make the plant susceptible to frost damage before your average date of last frost.

Frosts - avoid fertilizing less than three months before your average date of early frost or before your average date of late frost. Frost occurs when temperatures are between 0-6°C and the dew point, winds, etc are appropriate for the formation of frost. If you hear that there is a chance of frost, water the plant deeply, add mulch to maintain 7-10cms of mulch throughout the year and protect the plants with frost cloth or blankets (watch out when using heavy blankets that may bend r break stems though).

Anti-fungal sprays - these products should only be used when you have a fungal problem and identify the fungi causing the problem because their scope of usefulness is when applied to the fungi that the product was designed to deal with only. The most common leaf fungal issues with hydrangeas are powdery mildew and cercospora leaf spot.

What to do - they will go dormant soon so I would do nothing. If the fertilizer makes the plant grow new foliage, the next frost/freeze may kill them and could affect (kill) some stems. Stems that fail to leaf out by November-ish (mid to lat Spring) can be considered dead and can be pruned all the way down).

What else could it be - at other times of the year, it could be caused by nutrient deficiencies in phosphorus.