Espoma - there are two versions of this acidifier product making the rounds. One has a fertilizer + acidifier and the other is just a soil acidifier. If you want to strictly lower the soil pH to prevent iron chlorosis on the leaves then use the one without a fertilizer. Only use a fertilizer in Spring as these shrubs are not hungry plants like roses (in future years, they can even feed off the decomposing mulch and your soil's minerals).

I would select acidifying products based on price. You can also research how much 'garden sulfur' goes for. Or aluminum sulfate (but do not use by rhodies and azaleas). Or iron-chelated liquids products. These amendments usually do not have temperature restrictions. I have added them with temps well above 100F.

I would not use fertilizers in the hot summer months.

Pine needles and pine bark mulch may lower pH of the top one centimeter(s) of the soil only ;o)) ... that is... not much to write home about... so use the other products for acidifying purposes per label directions but, maintain any type of mulch for mulching purposes year around..

Newly purchased shrubs usually have some of those round fertilizer pellets still around so it is usually not necessary to fertilize until Spring of 2020.

There are not temperature restrictions to using soil acidifiers. I would apply now, then 8 weeks later, then spring and fall thereafter. It takes a while to lower soil ph so good to start now.

Mulch really doesn’t lower pH, so use soil acidified as you planned. You may find that the rhodies struggle in clay soil since that is my experience. I learned thatI should plant a bit high and bring the mulch up over the root ball when planting rhodies in clay because hey prefer loose organic soil which the mulch will create as it breaks down and is added to over time.

You will also need to continue to acidify the soil as time goes on. Altering a soil pH is only a temporary issue as the soil will naturally tend to buffer any changes and revert back to the native pH....especially a clay-based soil.

There is also a limit as to how much you can change it. If you have a soil with an alkaline pH - greater than 7.5 - it may be an exercise in futility attempting to grow acid loving plants.

And mulch has NO effect on altering soil pH....even a very acidic mulch.

Iron chelates will not alter pH and you will need to overapply the aluminum sulfate for it to have any significant effect and that is very risky with regards to developing aluminum toxicity. Especially with rhododedrons or azaleas, which are extremely sensitive to it. Agricultural sulfur is really your best bet but should be applied at least 6 months before any planting.

Peter, I have a limelight (live near Bloomfield/Birmingham/Troy). What is your watering schedule like right now? We just got a good rain but for three weeks it was so dry. My limelight receives no fertilizing on my part and I do no soil amendments as the color of the blooms don't change.

An established limelight will need little to no supplemental water, even in summer.

For a newer plant, a good weekly watering should do the trick.

I watered between two and three times a week the first year and then only in times of extreme heat and drought. I am with guyground, water well this summer.

Peter, not sure if you are nearby to one of their retail locations but English Gardens is having a hydrangea workshop this Saturday.

pH is an exponential function ... so mulch will NEVER change such.. short of millennia ... and tons and tons of material... but it looks nice.. and smells nice ...

in our ground freeze MI ... do not FERT after sept ... you need your plants slowing down.. to go into total dormancy ... not getting all drugged up on uppers ....

soil amending would be a different issue ... doubt there would be a fall application issue ...

so make sure you get the right iponema ...

that said.. its fert content is so ridiculously low ... it probably wouldnt matter anyway .. but why risk it ...

i used to use garden sulphur... back in the day ... and then lost interest in high maintenance plants/girlfriends ... lol ..

ken

Aurora, I prefer Bordine's as I live less than a mile from one. I don't have the free time for a seminar, and why bother when I can ask questions here and get replies from all the garden all-stars?

I planted a bunch of trees and shrubs this year, been watering most of them about twice a week. I hate my clay soil, there seems like such a fine line between over and underwatering.

PS this heat wave is gonna suck!

Peter, I just checked my limelight after your post and I have some yellowing leaves myself. I am going to assume the heat is getting to them a little. Or the heavy spring rains?

If you are ever in Troy there is an interesting nursery called Telly's. From what I understand, they have a selection of Japanese maples that are not usually found elsewhere. I also like Bordine's as well as Ray Wiegand's (a bit of a drive but their inventory spans acres as they do a lot of wholesale business).

My hydrangeas have had yellowing of the inner leaves all summer. They are looking a bit leggy. The flowers are finally starting to come along, though. From my understanding, it could be not enough acidity or possibly overwatering. I am not too worried about it though.

Some hydrangea paniculatas tend to "show their feet" due to heat stress in the summer. The leaves down near the base turn yellow, including the leaf veins and fall. But not a complete defoliation... just a bit near the bottom. All you can do to help is keep them well mulched (no rocks mulch though) up to the drip line and maintain the soil as evenly moist as you can. Water only the soil when a finger inserted to a depth of 4" feels dry or almost dry. Try to get the soil moist to a depth of 8" when you water.Start with 1 to 1.5 gallons of water per plant and tweak as needed for your soil (do not count the mulch in those 8"). If there is a heat wave declared, you could use a chair or umbrella to shield the leaves from the sun or use other "objects" to block drying winds.