I don't know the best option - floor or no floor - but if you do put in a floor be certain to have a teeny tiny slope on it so that it will drain properly and not leave puddles that will become green and slippery. It would be worth spending a bit of time and getting it right. Sliuppery floors are scary, time-consuming and dangerous.

I just have gravel in mine but I wished it had some insulation under it.

Mine does not get muddy or slippery, but I think if it did have another layer of flooring it would help keep it warmer in the winter.

Even though mine does not get muddy it does get ground water through it under the gravel and you can definitely tell the difference after lots of rain.

I think cardboard would only harbor insects, mice and such.

I fight weeds in mine also, when I start to lose the battle I get some weed killer and put a stop to it. it does keep the pest population down if you keep it as weed free as possible.

This is the ideal greenhouse for my place. Maybe one day...

It takes advantage of the earth's natural (constant) temperature.

Here is a link that might be useful: Earth heated greenhouse.

I've had more arguments about this than on any other subject here. Since I've worked professionally in greenhouses for over 40 years I have great belief in my own opinions. Concrete is an abomination, pavers are for fancy not for real biology; gravel ruins drainage and leads to serious soil compaction and weed problems. Nothing gets muddy and also weedy. The floor should be living! 6" sawdust is excellent, and other mulch is good, even straw. this will capture nutrients, moderate humidity, encourage earthworms which are the key to drainage, over time will create tops soil and can be easily cleaned and weeded Much of my greenhouse is in beds, the aisles soak up the organic matter I put down and soften the ground for walking..

sand_mueller,

Thanks, I'm a lot smarter now.

Johnny

sand Mueller, I don't entirely agree with your opinion on gravel. I do not grow in the ground in mine. I would rather have a solid dry walk area.
I keep everything in containers in mine so I can move things as needed.

It all depends on how the greenhouse is used.

I seldom get enough rain at any given time for the ground beneath my greenhouse to get very muddy for very long at all, so we have left the ground in its natural state. At one point we had thick black plastic over it, but I didn't like the way it looked and it was slippery when wet so I took it out. Later on, I put down cardboard to smother out the weeds, and then lots of mulch on top of it. Of course, the cardboard decomposed long ago, and most of the mulch is now compost. Occasionally I add a new layer of straw or hay on top of the older mulch. Nothing in my greenhouse grows in the ground (except the weeds). Everything in it is in containers of one sort or another. There was a time when I thought I wanted gravel, but I know it is better to just use mulch and let it decompose to enrich the soil, so we never did get gravel to put in there. I always try to choose whatever method improves the soil in whatever I am doing at our place. I do have weeds spring up in there occasionally, but it probably would be a bad sign if they didn't......

In the rare year we have heavy spring rain that leaves the ground inside the greenhouse muddy, I just put down a couple of boards to form a walkway down the middle of the greenhouse.

Tree, If you are going to grow in the ground, I don't know that you'd want that gravel in there. If you're going to grow in containers, it isn't necessarily imperative that you remove the gravel, but I do agree with Sand Mueller that the gravel will compact the ground beneath it. I have enough trouble with compacted clay soil as it is, so I don't like to use any technique that causes more compaction.

Dawn

I tend to agree with you, sand_mueller. I am glad you posted.

The pebbles was the only place I had to put it. At this time
I don't want to grow in the ground but in the future I can dig it out. Im just trying to get it ready for my seedlings come spring.
Thanks all
Tree

I used both pavers and gravel in my greenhouse, both on pathways that will never be planted in. I think the pavers help moderate the temperatures. During the middle of a sunny afternoon, the pavers are quite warm. After sundown they stay warm for a while. We don't heat our greenhouse so that is important to us. The in ground beds don't get mulched because I have a bit of problem with damping off. But someone on another gardening site said that sphagnum peat moss will help with that so I will use some next time I start some seeds in there. The gravel gives me some place to walk that isn't muddy after I water the beds. I don't care if it compacts the ground. It's a permanent pathway.

Mulberry, that is what I will do if I ever decide to grow in the ground. I can rake the gravel back to a permanent walkway. I have weed barrier under my gravel so it isn't being pushed down through the dirt.

I do not get standing water in mine with gravel over clay. It set on a slope so the ground moisture just travel through its natural coarse through the dirt underneath. It's amazing how much water runs out of a hill here. these hills dry out fast but the low areas still get moisture for awhile.

If I ever decide to plant in the ground inside the greenhouse, I'll have to move the greenhouse inside one of the fenced garden plots in order to keep our cats out. That first year, or maybe the second year, we built raised beds along one side and I was going to grow stuff in them in winter, but the cats thought I was building them a nice warm kitty cat outhouse with big, deep beds of enriched soil. That put a halt to me growing anything in there. We moved those beds to the big garden, one wheelbarrow load of soil at a time. The cats don't bother the plants or the soil in containers in the greenhouse, but they wouldn't leave the raised beds alone.

Our greenhouse is sort of at the bottom of a slope because our neighbor's land to the south of the greenhouse is higher than our land, and that would be an issue almost anywhere on our property as their rain runoff mostly all runs downhill towards us. So, a little water stands there by the greenhouse (more outside of it than inside of it) when we have heavy rain, but we don't have heavy rain very often. Our clay soil doesn't drain quickly but we are always so rain-starved that I don't mind having a little standing water. It beats tripping over the cracks in the ground when no rain is falling.

Before we built the greenhouse, its site was a weedy mess, so the greenhouse sure was an improvement over what was there before. I always thought I'd have a paver or gravel walkway in there but we never got around to putting in that walkway and I discovered it works fine with just plain old soil under mulch. I was out in the greenhouse for a while yesterday and today and it is like walking into spring in the middle of winter. I really didn't want to leave it and come back into the house.

Dawn

With a 20-tree orchard and a 1/3 acre garden to mulch, we just don't have enough extra mulch to put in the greenhouse. I'm a bit reluctant to anyway because mice do get in there occasionally and I don't want them to have anything to hide under in my veggie beds. Our cats are able to get into the garden and they try to slip into the greenhouse with me, but I've about got them trained not to...and when they do I run them right back out.

We had three days of sun in a row. It was a balmy 70 in there yesterday while it was 45 outside and breezy. Today though it is cloudy again. I covered the veggie beds with sheets last evening and didn't even bother to uncover them today. I filled several 5 gallon buckets with water. Hope that helps some.

I have concrete lower block sides with insulating plastic panels above, regular plastic roofing for a roof, old clay tiles for the middle walkway and small river rock on both sides. Its 30 years old. Obviously, I don't have problems with weeds, and it is heated, with an old and very large Navy surplus sink. Its winter storage for all the landscaping clay pots we put out in the summer, plus rigged shelving and grow lights up high on one side to start seeds. Waist high shelving on both sides of the walkway. Both doors have screen and glass. Wouldn't change a thing. Good place for our pet daddy longlegs to spend the winter.