No they are not necessary. Simply a convenience to help inexperienced or exceptionally busy growers keep the soil surface from drying out and crusting over.

If you will be gone for long periods of time or unable to mist the soil surface as needed then they can be handy. Otherwise they are't needed.

However you will want to check more than once daily and be sure you plastic cover is well vented so that heat doesn't build up inside. Nothing kills faster than heat trapped inside a plastic tent.

Dave

I find that covers give me better germination for certain tiny flower seeds that need to be left on the surface of the soil, though for 95% of what I grow I don't use them. I suppose that if I were religious about misting the soil for those seeds, I could forget the covers, but misting is work I'd like to avoid. I just keep an inch or so of water in the bottom of the trays and most everything stays moist enough.

ThinMan

The domes to help the seeds germinate, and they also help to keep the fungus gnats out. If you let a fungus gnat get in there and lay eggs, you could end up with an infestation and fungus gnat larvae are known to eat/kill seedlings when they are still relatively small.

One of those tall domes can ensure that your seedlings get to the size so that they are no longer vulnerably to such pests.

Steve - you don't mean to imply that fungus gnats are a given, right? Because they sure aren't. We grow hundreds of plants annually for sale and never have a fungus gnat issue.

Fungus gnats are a symptom of potting mix that is being kept too wet and standing water in the area.

And the standard recommendation is that if one uses a dome it needs to be removed once the plants germinate. It is never left in place over growing plants. That will almost guarantee damp-off and soil fungus problems.

Otherwise, as i said above, their use is strictly optional, a personal choice. But please understand that commercial growers never use them and still mange to germinate and grow plants just fine.

Dave

I generally use them when wanting to get seeds to germinate, as the basement I'm in gets a little on the cool side.

However, this year I was lazy and made the mistake of planting seeds with different germination times. I took the dome off when the first seeds began to germinate, and I still had ones that germinated later.

It's a tool that can be used to make things easier, I think, but it won't make or break the growing process unless you're growing in a very cool area.

You need to avoid covering pots with plastics. The humidity dome are only required for rooting cuttings. Many growers make the mistake of thinking that they need the high humidity conditions for germination; which is an unfortunate myth. The high humidity and lack of fresh ventilation can quickly cause fungus in the soil or growing medium youâÂÂre using and the seeds can rot.

I do use the covers for germination, just to avoid having to mist often to keep the top if the soil moist.. Sugarbee--That's the only reason to use them. If your soil is moist on top so the seed is moist, without them then they will serve no purpose for you.

Steve--Fungus gnats eggs often come in the soil--even good soiless mix can have them--so covering the plants serves no purpose. They are easy to get rid of--simply water the soil with soapy water made with a bit of insecticidal soap. That kills the eggs and larvae so no more gnats

Covers can help heat up the soil if you are placing them in a sunny window.
I do this, but with a hole at the top to make sure they don't get too hot. It does speed up germination. Cover goes off once they sprout.

FOLLOW UP: Hey all thank you so much for all the input! I planted 24 pans of seeds on Sunday afternoon and placed them inside one of my greenhouses but decided I would watch them closely and not put on lids making sure soil was good and moist also no lights on just yet. Door is zipped closed and min/max thermometer is reading 69 degrees. Tues morn I planted 5 more pans. Much to my shock and delight Weds morn I awoke to GERMINATION!!! Cosmos and Zinnias have sprouted as a matter of fact 7 pans had little seeds poking up:) I turned on the lights and they are set for 16 hrs. After 1 hr of lights being on I checked the thermometer and was shocked to see it had risen to 74 degrees.Yikes!! Open the door!! Now that the door is open it is maintaining 73 degrees (awesome) By last night there were 14 pans germinating!! This morning there are 21 pans now in germination. I am so excited to see these little gems. Now onto the next challenge of not over watering and adjusting the light as needed. Looks like I will be transplanting in a couple weeks if things keep going as well as they are. Again thank you all for your valuable input!! One very happy gardener here:)

Glad to hear! :) Part of it all is experimentation. I can't make my basement that hot, so it helps me, but it sounds like you have the perfect setup!