Hello! Experienced gardener here but new to peonies. I bought two Paeonia x suffruticosa 'Godaishu' and put them in large fabric pots at the proper depth for zone 8/Mississippi. They have plenty of ventilation and I use a probe so I'm not tempted to overwater. I think(?) I'm fighting some kind of fungus? One plant has done nothing since it was planted in March, the other puts on some leaves but they wither immediately. I've done a few rounds of copper fungicide in the evening, but it's doing nothing. They get sun until 2pm. And the pots are a generous 20ga. Help! I just need to keep them happy for a year until our t house is built and I can get them in the ground. Are the pots too big?

What kind of soil are they in? We're the roots grafted, did they have growth on them when you potted them? If the soil stays too wet it could rot roots.
I moved a few hundred tree peonies over the last few years, most were in grow bags for at least a year. I did lose some but the vast majority did great. I keep mine in grow bags beneath shade cloth for late summer through fall, zone 8a AL, just think they'd get way too hot otherwise.

Liz—

They were grafted and had some growth on them when I potted them. Soil is A 50/50 mix of compost and regular potting mix. Too moisture retentive?

Planted in March? What is the source of the roots? Quality of roots is really important. Big pots should not be a problem but the contrary. Good luck!

Anyagoro—

White Flower Farm?

I have no experience with this source. Maybe other forum members can tell something.

Liz is going to be your best advisor on growing in grow bags. She has been quite successful.

Just be careful of too much water in the high heat. The roots can rot.

Sorry for the delay—I've found that adding a significant portion of perlite or vermiculite to the soil helps enormously with draining. That much compost mixed with potting soil is still too heavy and will retain too much moisture. Even with 50% potting soil I'd add at least 10-15%/volume (not weight) perlite or vermiculite. Add a temporary shade source if you haven't already and water less frequently, let the soil dry out an inch or more down before adding any water. Cinnamon is an anti fungal that you can safely add to the top of the soil, if fungal growth ins't excessive it'll combat it.
One of the issues with too much water is that the soil loses oxygenation. If the soil starts smelling in any way other than natural soil smell I'd remove the peony and start over with a lighter mix. In bags, if you're moving them at all, it's a compromise between drainage and having soil dense enough to settle around the roots well and stay in place when the bags are moved. The best I've found is using a raised bed mix and perlite or vermeculite, mix is roughly 70-75% to 30-25%, somewhere in that range. Since your grow bags are so large, think you said 20 gallon, doubt if you plan to move them so having the soil tend a bit more light won't be as big of a problem as it is for me.

This is an older pic, have more current ones on my phone, but shows how the peonies are doing in the mix as I described. I'll try to post a pic I took in the spring where I moved all of the tree peonies and Itohs to a different spot, more grouped to make sure all of those get planted this fall. This pic shows other perennials as well. Some of those perennials are just in normal soil, just depends on what I had on hand when I dug those.

Can't find a pic of after the shade cloth was added but this shows what the plants looked like during bloom season this spring. I added weeper hose on a timer since we don't live there yet, haven't seen them since mid May, will be back down there in 2 weeks! All 3 rows on the left side are tree peonies, right are Itohs and herbaceous I want to make sure are planted this year.

Thank you LizB! I'll definitely repot them with a lighter mix. Laura

Laura, you might want to give them even more shade, know you said they have late afternoon shade but if your zone 8 is like mine it's hot as heck before noon. I have my bagged tree peonies under shade cloth 100% of the time, think this batch was 30%. The reduction in air temp is noticeable when I step under the shade cloth and the surface soil temp in the grow bags is much cooler than the soil temp in the surrounding garden. The cooler soil should help with new root growth. This late in the season I wouldn't expect to see any foliage growth in zone 8 in the south. PNW seems to be having a weird spring/summer so all bets are off for gardening there this year.
A lot of places will send woody or tree peonies out in the spring, I've always had a hard time with keeping them alive even before I moved my garden to AL. Necessity forced my hand into keeping a lot of peonies in grow bags for much longer than I'd like—necessity and my of so obsessive need to buy every new one introduced! I still don't have the best method to water them in the bags, the weeper hoses I have seem to only put out a constant and steady flow of water for a few months before they need to be replaced. I have lost a small percentage to rot, a bit too dry is much better than too wet.
The specialty growers actually mark the depth for planting on tree peonies—it is much deeper than for herbaceous. White Flower Farm isn't a specialty grower so you probably had no specific directions. They sell grafted tree peonies, relatively young ones that are probably imported so planting deep is definitely needed so the herbaceous root doesn't start putting out herbaceous growth. The top of the fat part of the root where the stem goes in to the graft should be around 4" below soil level.
The pic below is from today. Heat index still over 100°, actual temp around 94.

All the above advice are right on! At this point in the tree peony's growth phase, it may actually benefit these new tree peonies if you put them in total shade outside where it is cool like under a tree. What they need more right now is cool temps to grow roots, not sun. Being in the shade also helps them not to lose soil moisture so you don't have to constantly water them. It looks like the trees are going dormant so there won't be any growths from now until spring. Do not panic. The important thing to watch out for is that they form buds which will become new growths in spring. I will take a pic of tree peony bud to let you see what this growth bud looks like on a peony tree stem and upload it tomorrow.