📌 Quick Summary (TL;DR): Warming Cold Greenhouse Soil
- 🌡️ The Core Problem: In early spring, the top layer of dirt in a high tunnel or greenhouse might feel warm, but just a few inches down, it’s ice-cold. Planting tender tomatoes in cold soil will severely stunt their roots.
- 💡 The Bag Hack: Dig your planting holes a week or two early. Scoop the excavated soil into black plastic grocery bags and leave them in the sun. Use this sun-baked soil to backfill when you finally plant!
- ⚠️ The “Seedling Shuffle”: Lugging heavy cell trays in and out of the greenhouse for hardening off is backbreaking work. Many growers opt to set up a mini cold-frame *inside* the greenhouse with frost blankets and a small space heater for frosty nights.
Tiffany (Julia) wrote:
I also lay it down outside, right along the foundation line, so the soil there warms up too…
But at night, that outside dirt is gonna cool down fast under just one layer of plastic. Now, a double layer with an air gap might work…
Wouldn’t it be better to dig a shallow trench around the outside perimeter, drop in some 2-inch (5 cm) rigid foam board, and bury it? Just thinking out loud here, making me want to try it, even though my foundation is concrete covered with dirt. My only worry is field mice. Wouldn’t that foam board just turn into a luxury winter condo for them?
Hey everyone! Well, I couldn’t stand looking at my 20-inch (50 cm) leggy indoor monsters anymore, so I hauled them out to the greenhouse today. I laid down a plastic pallet on the center bed, popped some hoops over it, and threw on a double layer: a frost blanket on the bottom, and clear poly on top. Plugged in a tiny space heater for the night.Yesterday, on the other end of the bed (also under plastic), I direct-sowed some radishes and arugula. Even though we had a hard freeze last night (ice on the pond!), they didn’t freeze. I also kicked the aster and cabbage seed trays out there. Set them up on upturned crates so they aren’t sitting directly on the freezing dirt. We’ll see how they handle the night! 🙂
Nessi (Nelya) wrote:
My lower back is absolutely screaming…
Nelya, that’s exactly why I refuse to lug them back and forth. My back can’t take it, plus the garden paths are icy in the mornings, it’s a total slip hazard!
Tomorrow I’m starting greenhouse prep for the tomatoes. First, I’ll turn the beds, then dig the planting holes. Here is my trick: I scoop the soil from the holes into black plastic grocery bags and just leave them sitting on the greenhouse paths.
This does three things: the beds warm up naturally, the open holes allow heat to reach deeper into the ground, and the dirt in the bags absolutely bakes in the sun. When it’s time to plant, I use that hot bagged soil to backfill around the roots!
Aleksan9ra (Ludmila) wrote:
This does three things: the beds warm up naturally, the open holes allow heat to reach deeper into the ground…
Ludmila, I think that’s a brilliant idea!
I actually had something similar happen by accident. Last fall, I pre-dug my planting holes and stuck empty 5-liter (1.3-gallon) water jugs into them. Come spring, I was absolutely thrilled with the results!
But in bags out on the pathway? That dirt will bake in just one day, and it’ll act as a thermal mass, radiating heat back out at night. You don’t even need that many bags, heavy-duty black trash bags work best.
Ludmila’s “soil in a bag” hack is brilliant for cold-climate gardeners! Tomato roots suffer severe transplant shock if placed in soil colder than 60°F (15°C). Pre-heating the backfill soil acts like a warm blanket for the root ball.Regarding Valery’s foam board idea, his fears are 100% justified. Never bury unprotected polystyrene foam around a greenhouse. Field mice and voles will immediately tunnel into it to build winter nests, eventually finding their way inside to eat your seedlings!
