I have a mini greenhouse I just bought yesterday 3/15/18 and put kale seedlings, sugar snap seedlings and lavendar seedlings in there. I have a thermostat reading 38 degrees inside. Is this too bad for the seedlings? What should I do? Should I find some small space heater? here is the greenhouse I bought. https://www.amazon.com/gp/product/B0757B8T3K/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
Kale is a cool weather crop that can be planted outdoors about a month before last frost date (which is around Mother's Day). It will probably be o.k. in there until you could put it out in mid-April.
Here is our page on kale: http://extension.umd.edu/hgic/plants/leafy-greens
Here is our page on peas: http://extension.umd.edu/hgic/plants/green-peas
Mid-March is an o.k. time to plant out the peas if you have a garden space ready to accept them.
This calendar will tell you the timing of planting seeds or seedlings in our area: http://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/not_update...
Lavender should be brought into the house. It normally would be dormant right now and we have more cold weather coming. It should not be planted outside until around Mother's Day. Make sure the area where you plant it is well-drained. Once established, it can take dry conditions.
It doesn't always grow very well here because our winters tend to freeze and thaw in cycles.