First you need to understand that it isn't really a greenhouse, it is just a tray with a lid on it. So unlike a greenhouse it traps both heat and moisture and it prevents any air circulation. Conditions that are potentially lethal to both seeds and plants IF they germinate. Many discussions here about those problems.

Second, since you mixed all sorts of different seeds, each with different germination times and temp requirements, your germination will be very sporadic and over a prolonged period of time. For best results in the future only do 1 or 2 types of seeds in each tray and do them in individual cell packs or containers so they can be removed as they germinate.

Third, since I live in zone 9, the temperature of the mix never really drops below 70 degrees isn't accurate. There is little correlation between air temp and soil temp and it is soil temp that matters. Most seeds need soil temp between 75 and 90 degrees and the air temp just can't supply that. Soil temp will always be 10-15 degrees cooler than air temp. So you need to add bottom heat to bring the soil up to germination temps. Lots of discussions and a FAQ here on how to do that.

Fourth, soil temp problems are compounded by the use of deeper containers such as the pots. It only takes 1" of soil to germinate seeds. And as you discovered with the baggie method, not even that much. Deeper containers with more soil that the 1" can't get warm enough for germination. So the tray and cover deal can work but you need to use shallow containers in it with only a bit of soil and bottom heat.

All the other problems with the Jiffy pots I'll skip for now since you are already using them but there are many discussions about them you'll want to review for future reference.

Right now, given what you have described, bottom heat of some source it going to be about all you can do. That and some patience and avoiding overwatering should solve most of your problems.

Hope this helps.

Dave

May I ask where you have been keeping this jiffy greenhouse? I have a sneaking suspicion since you mention your zone and the temperature that you might have it outside in the sun. Tell me I'm wrong! :)

Lol, yes sleepy, I have been following the instructions that came with the jiffy greenhouse, one of which is to keep out of direct sunlight. I keep it on my front porch which is warm, but gets no sunlight.

Dave, I am aware that the pots should be moved once the seedlings emerge. I have already moved all of the germinated pots into a sunny window, or transplanted the larger seedlings. I was unaware, however, that the soil temperature could be that much lower than the air temperature. It's about 9:30 right now, and it's about 77 degrees outside, so I suppose that soil temp could very well be an issue. Thank you for your help.

Well, out of direct sunlight is good! What type of seeds are they, that you are waiting to sprout? That might help to know if they are slow germinators, or particularly prefer bottom heat, etc.

I would add just one other comment. I have found (and read) that potting mixes with fertilizer in them can sometimes inhibit germination. Just a thought if you used different soil in the greenhouse than in the baggie.

The seed starting mix that I had doesn't say anything about fertilizer. it just says 100% organic.

And I am still currently waiting on some 4 o'clocks, zinnia, and Dahlia. I have had some zinnia and 4 o'clocks sprout already, but I have yet to see any dahlia seedlings...

Are the seeds dead if the it was left in direct sunlight for a few days?