Shade Gardening forum: Advice on soil amendments for shade bed with acid-loving plants (Zone 5B)

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Upstate New York (Zone 5b)
sah67
Mar 31, 2018 6:54 PM CST
We're planning a new shade bed under a large Pin Oak in our Zone 5B backyard. When we bought our house last spring, the area was overgrown with weeds, brush, and landscape fabric (ugh!), but we cleaned it up enough to plant a few things, including a Rhododendron 'Nova Zembla', a few Bleeding Hearts, a Smooth Hydrangea and some Columbine. We had a lot of other projects to get too though, so we weren't able to turn our full attention to it until this year.

It's about a 250 sq ft. space and we're envision turning it into a 'wild'-looking, shaded woodland area, and plan to add several more Rhodo's/Azaleas, Tiarella, Hosta, Astilbe, Fothergilla, Asarum, ferns, etc.

We're going to be sheet-mulching the whole area in a few weeks to make sure we have a nice clean area in which to plant later this spring, and having tested the soil last week, we know that it's already slightly acidic (about 6.2 or 6.3), but most of the plants we have in mind really like an acidic soil, so we were wondering if we need to amend to get the pH any lower?

As part of the sheet mulching process, we're going to add shredded pine bark mulch as the top layer, which may help some, and we were also thinking about adding some HollyTone, just to give some of the Rhodos/Azaleas and other acid-lovers a boost when they go in, but I'm a bit confused about the proper application. The Espoma instructions say to broadcast the product widely across the new planting bed, but should we instead be spot-applying the HollyTone to the planting holes for each plant, and not cover the whole bed?

We've also seen some conflicting advice about timing of application of the HollyTone, with some sources saying that it's best applied when planting new Rhodos/Azaleas, etc., but others saying it's best applied right after they're done flowering...perhaps that's only for established plants though?

Is HollyTone even the right idea, or should we being using a true soil acidifier like Sulfur? Or should we even just hold off on amending now until we get a sense how well everything "takes".

The Nova Zembla we planted last spring is doing reasonably well without any amendments other than compost at planting, and it has shown some growth and increased flower bud development this spring...so maybe we're overthinking things!

Any feedback would be greatly appreciated...thanks!
Name: Cindy
Hobart, IN zone 5
aka CindyMzone5
Celebrating Gardening: 2015 Plant Identifier
Shadegardener
Apr 1, 2018 7:28 AM CST
sah - Sounds like a fun new project. The pH seems perfect for acid-lovers. Any rhodies and azaleas you plant will already have flower bud formation started last year. So you should be okay to use the Epsoma when you plant. Next year, you can fertilize after blooming. And because they're shallow-rooted, top-dressing with peat moss would be beneficial both as a pH-modifier and to keep the roots from drying out. I wouldn't use the shredded wood mulch on top. You can also top-dress with compost under the layer of peat moss. The main thing with planting under an established tree is to find pockets of decent soil under it and to provide adequate moisture. The tree roots will dominate in taking up moisture and sometimes the tree canopy can somewhat inhibit rain from reaching your new plants. Keep the sheet mulching shallow around the tree trunk and on top of tree roots as it's not a good thing to build up the soil level around them.
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize that we can't eat money. Cree proverb
Hurst, TX (Zone 8a)
Dog Lover Region: Texas
luis_pr
Apr 2, 2018 11:23 AM CST
I apply organic materials (compost, etc) to the whole bed but I only amend for acidity near the acid loving plants. Basically, under the drip line plus a foot or more. If the shrubs that you have, have been pruned a lot, their roots may extend longer than the shrub so adding amendments further away makes sense then too. I use whichever amendment I happen to have handy in Spring and Fall. That usually means either Espoma's products, greensand, garden sulfur, aluminum sulfate (keep this one away from rhodies and azaleas but a/s is ok near hydrangeas, either bigleaf or smooth hydrangea), iron-chelated liquids, etc. I just apply when they all have leafed out and I have the time to add fertilizer and amendments. Being so specific as to exactly when to amend is too much for my schedule and does not hurt if you are off. Consider that the plants will typically develop iron chlorosis signs if you are "late" amending so let them tell you to hurry it up then. If they do not "complain", I live them alone in the Fall. I already know that if I do nothing in Spring, I will "hear" about it.
[Last edited by luis_pr - Jun 21, 2018 12:38 PM (+)]
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Name: Virginia
Charleston, SC (Zone 8b)
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scvirginia
Jun 20, 2018 11:43 AM CST
I wonder if you really need to amend at all to lower the pH? I think all the plants you listed will be fine in the neutral to slightly acid range, and I think a lot of ferns prefer neutral to slightly alkaline.

I'm bone-lazy, so take this with a pillar of salt, but I think I'd see how things go before trying to change the soil pH.

Your plant selection sounds great.

Virginia

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