I have four cold frames that I made using plastic storage bins and two more that use glass with the thermal mass of bricks and stone. These are experimental and so far I’m seeing some clear differences in the results.
The seeds started in the thermal mass cold frames are thriving and growing much more quickly than the others. While not the exact same varieties, there are tomatoes and peppers started in both the plastic frames and the glass-brick frames.
There is one cold frame in particular (Cold Frame 4) where the seeds are ESPECIALLY slow coming up. I have only spotted one seedling in here so far:
Compare with Cold Frame 3, started on the same day:
And the big difference is with Cold Frames 5 & 6 which have the advantage of thermal mass keeping them warm at night. These were started a couple of weeks AFTER Cold Frame 4 but are growing much faster:
I have a couple of ideas about why the seeds in Cold Frame 4 aren’t coming up, or aren’t coming up as fast as all of the others.
The thermal mass surrounding Cold Frame 5 and 6 are certainly helping keep the seeds and seedlings in there warmer at night. In the desert environment here it gets a lot colder at night than it is during the day. (Why? Humidity in the air keeps the temperature more stable. You’re welcome.)
But the other plastic cold frames are also doing better than poor Cold Frame 4, which is the lower container below:
I’m guessing that perhaps the height on the other bins is somehow allowing for more warm air to accumulate, keeping those seedlings warmer at night too.
Or, perhaps when the plastic cold frames were next to the house #4 took on too much water one night and washed all the seeds out of the pots. It’s possible!
In any case, it’s a good learning experience. Next time I will go with thermal mass all the way. And perhaps for the time being I’ll go out and pile up some bricks next to Cold Frame 4 and see if that helps.
This episode of geeking out in the garden has come to a close! More garden geekery next time!