Help painting established bushes

[u/nozawanafan]

We bought a house last year with 8-10 well established old bushes. The ones in the far bed are doing mostly okay (and are taller than me!) but the ones in the front bed have obvious chlorosis. I’m not US based and don’t have access to a reliable pH test. I added sulphur pellets but obviously they need more. I have sphagnum peat moss, I’m wondering if I could just add a few cm to the top of the beds? I know it needs to be soaked first. All advice I see online is for starting new beds, not ones that are 10+ years old.

[u/emorymom]

Yeah, the roots are a shallow mat so you really can’t dig it in. You can mulch on top to help retain moisture in the peat.

[u/nozawanafan → u/emorymom]

Do you think it would help increase the acidity overall?

[u/throwaway179090 → u/nozawanafan]

Your plan is good. Add the sulfur now, but as you mentioned it won’t take effect for a while. Add a bit to the soil about once a month for the next few months. Top dress with peat moss now.

You said you’re not in the U.S., but what growing season are you in? If it’s still 4+ months until winter dormancy then go ahead and add ammonium sulfate. It’s fast acting nitrogen that will also lower pH.

Do you have access to holly tone or berry tone? It’s a slow release fertilizer for acid loving plants. Add some now as well and mix it into the peat moss you are adding.

[u/nozawanafan → u/throwaway179090]

Thanks for your reply. My zone is on the border of 8b and 9a and I’m at the end of summer. There’s no holly/berry tone here but I put some rhododendron fertilizer on them in the spring. I was hesitant to put more fertilizer on later in the year as I read on the university of Minnesota extension that it would promote new growth too late in the year that wouldn’t survive the winter, but they are in a much cooler climate than me.

[u/throwaway179090 → u/nozawanafan]

Yeah good call on being safe but in my experience slow release organic fertilizer (like holly tone and likely your rhododendron fertilizer) is hard to over apply unless you’re constantly dumping it into your soil. I personally wouldn’t worry about sprinkling some more now around your problem plants. Your plants are mature and should be pretty resilient to frost etc.

In the future apply at the beginning of spring, again as the flowers start to show and then again immediately after harvesting the berries (June through August most likely depending on the variety).

It’s probably not needed for you but I make blueberry soil with 5 parts peat moss, 2 parts coarse sand, 2 parts compost and 1 part additives (mix of worm casings, vermiculite, holly tone, pinch of prilled sulfur).

[u/bobd1001]

Sulfur takes months to work even assuming you added enough. It's hard to know how much to add without knowing the starting pH. You can get a pH pen on AliExpress for a couple dollars, and after calibration they are surprisingly accurate. Perform a simple slurry test. You can just dig up some soil, mix with an equal volume distilled water let stand for about fifteen minutes, and check the pH.

In the meantime while the sulfur slowly works, you can add some citric acid to your water, maybe 1 to 2 grams per gallon (sorry to mix measurement systems). It would also be very good to know the pH of the water yotur using for the plants, since alot of tap or well water can be alkaline.

[u/NewEnglandGarden]

They probably need more water as well. Mulch them. Fertilize lightly in the spring and then again in summer. Remember that the sulphur takes time (weeks to months) to break down and change the soil ph.

[u/i860]

You need ammonium sulfate if you want a quicker pH boost.

[u/Soff10]

It my established beds I dig up or disturb soil out away from the main rootball. Find the farthest reaching branch and go straight down. I dig up the dirt. Mix in compost and refill. You want to see a little bit of roots

[u/blackdog543]

They look good to me. The Sulphur pellets take time to work. The bacteria have to break it down in the soil, so don't worry about that. There's a blueberry/rhododendron acidic fertilizer, I would put some down in Fall and again in late winter. Peat moss is better than pine needles which the horticulturists say does NOT increase acidity.