Limelight Hydrangea Trees— It’s September in Rochester New York, the same climate as Toronto. We had an unusually hot weekend in the 80s F. Returning home from a trip I found my limelight trees had entirely yellowed in the interior. They were newly planted this June and have had a strong summer with good growth and beautiful blooms. Now I fear they will die off. 2 inches down is moist soil as we now have had rain. If the trees need iron should I fertilize this time of year?
What your Hydrangeas are suffering from is stress related to lack of moisture and unseasonably high temperatures for this time of year. This stress will make the leaves turn yellow and drop, but that being said, rest assured your plants are not dead. Water them well over the next few weeks and continue doing so until the ground freezes. 20 minutes / twice a week with a drip irrigation system or soaker hose is ideal. Remember that “Hydra” means water, which aptly describes these thirsty occupants in your garden.
Now is not the time to fertilize as this might spur the plants into producing new growth right before they head into dormancy. This new growth will not have time to harden off and would likely succumb during the winter. Early spring when the weather has warmed up and the ground is workable is the time to start thinking about feeding them.
A general all purpose fertilizer of 10-10-10, either chemical or organic, should be sufficient – follow manufacturers instructions exactly as recommended. If it is a fast release fertilizer, then apply in March/early April, again in May and lastly in July (3 times). Apply to the soil around the plant at the dripline. For a slow release fertilizer, one application is all that is required in April. Apply around the plant and then scratch or fork it into the top layer of soil and then water well.
Iron should be applied twice during the growing season in order to keep the leaves green and healthy looking. This can be done in April and July.
Top dressing around each plant with a well rotted manure, compost or worm castings will improve the overall heath and structure of your soil. Mulching will also help with moisture retention and keep weeds in check.
Although your plants are new, you should consider a light pruning in the late winter or very early spring. Do this only to remove any dead, damaged, diseased or crossing branches. Once your plants are more established, you can prune for size and shape.
Good luck.