too much lime???????

8 years ago

Hi,

I've tried a new soilless mix this spring for my new roses. This is the highly acidic peat moss, bark fines and perlite version. So a lot of my roses ended up getting powdery mildew, because I didn't know that I had to add lime. Duh. :) Anyway, most of them are doing well since I applied lime (calcium carbonate). But some (about 4 out of 18 new roses) have persistent powdery mildew, and I wonder if I have over-limed. Can over-liming cause powdery mildew? I don't know how much lime I've added, because each rose has been different....but maybe 2 cups/plant for the ones that didn't get better. Should I keep adding lime? Or do you think I've over-limed. Sigh. Or maybe they're fine...but I just need to apply milk/water mixture to the leaves?

Thanks....I'm STILL (after all these years) learning. :)

Carol

Featured Answer

rhizo_1 (North AL) zone 7

8 years ago

What on earth does lime have to do with powdery mildew? By any chance do you mean lime sulfur?

IF a potting medium is excessively acid, then the appropriate remedy of a lime amendment would be in teaspoons or tablespoons, not cups. I am assuming that you are growing the roses in containers, right?

Homemade mixes often require the addition of lime but the commercial products are already pH adjusted.

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Comments (6)

rosecanadian
Original Author
8 years ago
This was mixed for me by a company, but it wasn't pH adjusted. Yes, I'm growing them in large containers.

I was just wondering if excess lime might cause pm.

Thanks,

Carol
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Moses, Pitt PA, cold W & warm/humid S z6
8 years ago
last modified: 8 years ago
Rosecanadian,

I do not know if excess lime promotes powdery mildew, but I do know that some varieties are more susceptible to it, of them, some are extremely so. Also, a powdery mildew outbreak can be a dickens to turn around, worse than black spot in that regard. Still, black spot is more a constant issue for me, compared to the very specific window of opportunity powdery mildew needs here, namely: cool nights, hot days, along with dry foliage...fall and spring (mostly fall), not usually summer.

I would just follow a regular powdery mildew spray program, water your roses faithfully, as I am sure you do, and in time, the lime amended soil will adjust as it it is flushed by your watering.

You may try giving a few Miracid feedings to the affected roses, then see what unfolds.

How's your Grand Dame doing this year?

Moses
rosecanadian thanked Moses, Pitt PA, cold W & warm/humid S z6
rosecanadian
Original Author
8 years ago
Moses - you're probably right...the affected ones are: Dolly Parton (known for pm), Lucille Ball (always gets pm for me), and a few others that don't have a tag and no blooms yet. I think I fixed the pm problem that the roses were having with the acidic soilless mixture. The rest are probably just known for it. And we do have cool nights here as we're close to the mountains. Thanks for helping me with this. I fogot about them being prone to pm.

My Grande Dame is doing very well. No flowers yet, but the bush has a wonderful shape to it and there are many buds. :)

Thanks, Moses.

Carol
Embothrium
8 years ago
last modified: 8 years ago
the pm problem that the roses were having with the acidic soilless mixture

The only relationship between soil medium and mildew incidence that I am aware of would be a coarse mixture drying out frequently, with the associated recurring chronic dryness at the root encouraging mildew.

What foliage mildew spores like is genetically susceptible plants with drought stressed roots and damp - not wet - foliage. So the rain-less yet eventually dewy and foggy summers of the Pacific coast for instance are probably just about ideal for them.

And you can actually reduce the amount of mildew on plants by hosing them down - in the morning.
rosecanadian thanked Embothrium
rosecanadian
Original Author
8 years ago
Thanks! I'll try the hosing down in the am.

Carol