The 13x15x9 ft. GH that I am restoring in North FL had a hard dirt floor which drained reasonably well when open to the weather (GH glass panes broken out). I had some old 8x16x2 inch pavers (concrete with little rocks mixed in), so I simply laid them on the dirt, totally covering the floor area. They have remained level for many months. I have since learned that I need a weed barrier so I am now taking the pavers out.
After reading many posts here on greenhouse floors, using pavers for walkways and gravel under benches, etc. I think I would like to cover the entire floor with pavers.
When I reinstall them, can I just use online instructions I have found for installing a dry-laid walkway (essentially, sand tamped down to 1 inch), or is a greenhouse different? Charley's Greenhouse recommends
3/8 inch spacing between pavers. Does that sound okay? Thanks. T-L
3/8ths of an inch isn't that much, follow what the greenhouse instructions say. Lay the weed barrier down, put a good three inch layer of sand over that, and then set your pavers down on the sand. Don't forget to sweep builders sand into the cracks after you lay the sand foundation and set the pavers in. Sweeping the sand into the cracks fills up the cracks with sand, which you then sprinkle with a fine mist of water. If the sand settles, sweep more sand into the cracks to finish filling up the cracks and resprinkle the pavers to set the sand. madgardener
You might consider leaving the walkways just a bit higher than the rest of the greenhouse. The walkways tend to get compacted with use (and therefore resist drainage), so starting with them higher will force water to run to the uncompacted areas. Otherwise, the walkways will sink a bit over time and water will collect there. You don't want to leave a step up to the walkways, just tilt the pavers on the side so they slope away. How much higher depends on the soil underneath and how much it is likely to compact. My first greenhouse with a loam floor compacted around 3". However, this was with just a woven poly weed block, so the compaction was basically caused by foot traffic. The pavers will spread the load out over a larger area, so the compaction should be smaller.
Two other possibilities: (1) you can take up the pavers and add more sand under them if you do get compaction, thereby raising the walkways, or (2) you can add a fairly thick layer of coarse sand for drainage under the pavers when you install them initially. I would recommend 6" for good flow. Of course that means you have to take out some of the underlying soil (unless it's really sandy) or else you may have to step up to get into the greenhouse.
Putting sand on top of the weed barrier certainly won't deter weeds. Whatever weeds there are will surely take root in the sand.
Forget the weed barrier.
Put down 3-4" of sand. Level the sand. Soak the sand good with water so it settles. Put pavers on top of sand. I would but pavers up to one another and not worry about filling the cracks. Whatever water you may have will find its own way through the cracks.
One problem you should watch for is ants and other burrowers which may undermine your handiwork. I've reworked patios "damaged" by ants.
But Charley's does not say where to put the weed barrier. The Charley's text suggests that it is to go under all of the "loose floor material," but I thought perhaps the weed barrier could go between gravel and sand, to keep the sand from going down into the gravel.
Early in this project, I reported that I had put down pavers without a weed barrier, was getting weeds, and asked about using Round-Up in a GH. I believe the advice I got was take up the pavers and start over, with a weed barrier. Charley's Greenhouse says, "Before laying down a loose floor material it is important to remember the weed barrier to prevent weeds taking over. ...." It seems that GHs are art, not science, and that "best practices" are yet to be determined. Thanks for all help. T-L
Last summer I worked in a nursery which had hoop greenhouses. Their floor consisted of pea gravel over weed barrier. I doubt whether they had sand beneath the weed barrier. I still saw weeds.
Since you are using pavers, maybe weeds won't be much of a problem except around the edges where walls meet floor. If I were to have my own GH, I would consider screen doors and screens over all openings. I would also resign myself to pulling weeds.
You're going to do just fine with your GH. As you tweak it to suit your needs, you will make it more workable. Have fun!
You don't say how large your greenhouse is or what size slabs(Pavers) you are going to use. Why not sand to level then weed barrier then slabs. I would be more inclined to lay weed barrier, then just lay a 1 1/2 to 2inch layer of cement to make the path, and the same depth of gravel under the benches. What ever you do you will always have a few weeds but the pull easily enough. and some plants will love the atmosphere under the bench.
If drainage is your main concern then forget everything and just use the gravel. I would use Rice Rock - a very fine gravel that you could walk on barefoot. Not as comfortable as sand, but still walkable. Put it down around
4" to 6" and when you get weeds just spray with Round Up.
Greenhouses have weeds. No matter what you put under foot, you are going to be working with growing media. You will spill some, some will wash out of the pots/cells, organic material (leaves, cuttings) will collect in inaccessable places and compost. All these things support weed growth. The only thing you can do is remain vigilant and try to address weed problems early, before they become established.
Weed barriers prevent leaves from coming up through. They do not prevent roots from going down through them. If you get a weed growing on top of a weed barrier, it will put roots through it, after which it becomes very difficult to deal with, since removing all the roots damages the weed barrier. Removing only some of the roots allows the weed to re-grow. Get the weed before it puts down a significant root structure.
Use of Glyphosate in an active greenhouse is difficult since you have to avoid drift. If you have to use it, it's best to use it when there are no plants there. Greenhouses do accumulate crud. You should schedule some time during the year to empty the house and give a thorough cleaning.
There is a rule of thumb that seeds will only germinate if they are buried less than seven times their maximum dimension. (This applies to the field, where temperature fluctuations are large and may not really apply to greenhouses). Since you are not disturbing the soil in the greenhouse, you may get an initial flush of weeds from sand as the upper layer of seeds germinates, after which you will only get weed seeds that are brought in from outside (unless your indoor weeds go to seed).
I use a propane torch to kill weeds in the field to form stale seedbeds for direct seeding things like carrots. This is difficult inside the greenhouse if you have something like a woven poly ground cover floor (although you might be able to wet the floor first and minimize damage, I wouldn't count on it). With pavers, you might get away with it. However, using a torch inside a greenhouse presents other problems such as avoiding flammable coverings and carbon monoxide if the greenhouse isn't well ventilated. Glyphosate might be easier.
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