Are my new planting beds too hot to plant anything? - Ask Extension
This past weekend I had landscapers install new planting beds using Leafgro and topsoil. When I dug into them to plant my first plants, I found that ...
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Are my new planting beds too hot to plant anything? #870161
Asked May 26, 2024, 2:39 PM EDT
This past weekend I had landscapers install new planting beds using Leafgro and topsoil. When I dug into them to plant my first plants, I found that the compost was still really "hot" -- steaming, to be exact. When I used a laser surface thermometer, it was reading between 95 and 98 degrees, but when I held a handful of the bed mix it felt a lot hotter than that. I'm really afraid that my dahlia tubers will cook like potatoes in this stuff. I've planted 4 already, and I think I'm going to stop and set the other 16 aside for after I receive your feedback.
It's supposed to rain tomorrow and cool down into the 70's by Tuesday, but the soil may still be cooking even if the ambient temps are milder. It feels like heat from a chemical reaction, not just from the sun (although it's really hot outside today too. I think it's 86).
How long does it take for compost to cool down? It is mixed with soil, but I'm guessing that they may have used a higher ratio of LeafGro than is desirable.
Is there anything I can do to cool this soil down or stop whatever chemical reaction is happening with the LeafGro?
I was hoping to plant my zinnia seedlings in these beds too. They're about 4-6" tall and ready to be planted---but I think they'll cook too, despite the fact that zinnias like full sun. The soil just seems too hot.
I know that at some point the soil will normalize, but I have no idea how long it will take. I'm hoping you will.
Can you please let me know what my options are?
Thanks!
Anne Arundel County Maryland
Expert Response
Hi-
The Leafgro was likely immature and/or stored in too deep piles. We expect the soil/compost mix to have cooled considerably by now, especially if the beds are <8-in. high.
Soil temperatures in your area are around 70 degrees F. If the soil temps read <80 degrees F. in your beds it is safe to plant.
Jon
The Leafgro was likely immature and/or stored in too deep piles. We expect the soil/compost mix to have cooled considerably by now, especially if the beds are <8-in. high.
Soil temperatures in your area are around 70 degrees F. If the soil temps read <80 degrees F. in your beds it is safe to plant.
Jon
The new beds were filled 18” deep with the soil/Leafgro mixture. I measured the temperature again after I sent you the first message and the reading was 117 during the afternoon. It was actually hotter the deeper I dug. I’m about to go out and dig again now that it rained and see if it made a difference.
Wow... are you smelling ammonia, hydrogen sulfide, or other odors?
With 18-in. deep beds it could take a week or more for the temperature to come down to an acceptable level.
The Leafgro will continue to decompose. You could accelerate the process some by driving a garden fork into the beds and rocking it back and forth, lifting the fork out and moving to the next 1-ft. section.
The pH of this hot mix may be a bit high but that too will decline to an acceptable level. As long as there are no off-smells, you could plant once the temps drop.
Jon
With 18-in. deep beds it could take a week or more for the temperature to come down to an acceptable level.
The Leafgro will continue to decompose. You could accelerate the process some by driving a garden fork into the beds and rocking it back and forth, lifting the fork out and moving to the next 1-ft. section.
The pH of this hot mix may be a bit high but that too will decline to an acceptable level. As long as there are no off-smells, you could plant once the temps drop.
Jon
Thank god I don’t smell any strange smells! Just a normal rich soil smell—but despite the rain last night and cooler temps today, my new bed that has total/all day sun exposure is still 123 degrees. I used a soil thermometer this time. I tried watering it deeply, but that only reduced it by 10 degrees.
It’s strange—some areas are 120-123 degrees 6” deep and other parts of the new area are only 100 or 95. I checked some of my regular/old bed and soil temp is between 78-80…so soil is pretty warm today anyway.
I’ll try you “mixing around” suggestion and hope to try again to plant in a week, I guess. The zinnia seedlings I’ve been growing since late March are ready now though ♀️
Sent from my iPhone
Sent from my iPhone
On May 28, 2024, at 1:17 PM, Ask Extension <<personal data hidden>> wrote:
Hi- don't water the beds unless they fry out. Aim for the pore space to be 50% air and 50% water (soil stays moist but not wet) to accelerate decomposition. Good luck!
Jon
Jon
What does “fry out” mean? The soil is extremely dry very far down (at least a foot) despite the thunderstorm last night. Today I watered one spot for about 3 minutes, waited 20 minutes, then turned over the soil. It was wet on top but dry below that. I think the mulch soaked up a lot of the water.
I’ve scraped off all the mulch and put it in a wheelbarrow for now. I’m going to dig up and turn over the bed and break up any compost clumps I find. This should help break up any compost-only layers. The workmen didn’t mix it very well, it seems.
I pulled up the 4 tubers and their sprouts were brown and soft. It looks like they’re probably not viable anymore.
I feel like this soil needs a good drenching to get it started off because right now it seems like, despite the rain last night and my watering this morning, it’s really dry. I picked this mix because of it’m drains well, but I do need it to hold SOME moisture. Should I mix in some vermiculite? I have a huge bag of it.
Sorry- "dry out."
You are doing the right things-
Mixing in the vermiculite at 10-20% of the total volume would be fine.
Jon
You are doing the right things-
- moving the mulch aside will help more air and water get into the soil mix they brought.
- watering to moisten the entire 18-in. depth of the soil mix.
- breaking up compost clumps and aerating the beds.
Mixing in the vermiculite at 10-20% of the total volume would be fine.
Jon
