Best Base for Greenhouse?

I'm about to order my first green house. I've settled on a wooden frame greenhouse with toughened glass, because it can get pretty windy where we live.

It'll be 6x10ish and i'll need to prepare a level base for them to install on.

The area of garden i've chosen is currently turf, so can install pretty much any base.

I think for the frame support i'm looking at pathing slabs, but the question is for inside the greenhouse am i better to just pave it all? Or pave a rectangle, and put gravel in the middle to allow better drainage? Or indeed am i better for something like tomatos digging a trench into the ground , lining with weed barrier, refilling with compost and effectively planting striaght into the ground?

Any thoughts and advice are well recieved.





  • sotongeoffsotongeoff Posts: 9,806

    I can only tell you what I have-paving down the middle-gravel on the remaining soil-removable staging

    I have never grown direct into the soil as it means replacing frequently to stop a build up of diseases-much prefer to grow in pots.

    I suppose it-all depends on what you are going to use it for -will it be heated?

    There are penty of greenhouse growers on here who will possibly weigh in with thoughts

  • Gary HobsonGary Hobson Posts: 1,892

    I can only tell you what I have - fully paved. Mine is mounted on heavy 3'x2' concrete slabs. You do need to ensure that the ground beneath is stable and won't compact. If you are situating the greenhouse on the site of an old lawn, then that is more likely to be compact and stable, than if it was on recently cultivated soil.

  • I have a 12ft x 8ft greenhouse, i dug out the area to a dept of 2 ft, put in a 6inch layer of hardcore to allow good drainage , then poured a rectangular area of concrete 6inches deep and 8inches wide around the edge, i then laid a single row of full size concrete blocks on edge and fitted my greenhouse base to that, i have a central path made from slabs (2 wide)   18inch x 18inch down through the centre, i then filled in the remaining area with a mixture of well rotted manure, topsoil, weeded garden soil and sharp sand, 

    I do plant directly into it, it drains really well, i will need to top it up yearly but i do use the soil from the greenhouse in pots when im potting things on, so it will be rotated.

    It was a lot of work but i will certainly do it again when i fit my next greenhouse later this year.


  • AtillaAtilla Posts: 1,493

    Paving is better in a 6X10 greenhouse. Soil keeps the greenhouse damp in winter which encourages mould on plants ,and, in spring and summer allows all manner of things to crawl in and eat what is in your greenhouse.

  • Zoomer44Zoomer44 Posts: 2,902

    My GH is mounted on paving. Inside it's paved on one side, with a gravel path down the centre and a bed to the other side. There's ample room at the top and near the door to have plants growing in buckets either side of the bed on the paving. 

    The paved side means I can have a potting bench the length of the GH, which stands on a hard surface and can store pots underneath. At the height of the growing season the bench houses pots of low growing veg like chillies, peppers and aubergines.

    I grow direct in the bed and the soil does need to be changed although I also grow in bottomless pots so just change the top few inches. Never had a problem with pests getting into the GH through the bed but as blairs pointed out GH does get damp over winter, hadn't realised it was the soil causing the damp and this could be a problem if your GH is made from wood.

  • I was a complete novice but reasonable at DIY, I ordered a 12' by 10' GH and then started on the ground prep. My GH stands on paving slabs which are 2' square. It has gravel that is 3-4" deep on the inside with a paving slab 'path' down the middle. Having studied numerous  laying paving slab vids on the net, acquired the necessary tools, I started laying the slabs.. It looks so easy on the videos to mix up a dry sand/cement mix then lay the slabs on it, trust me it is not!!! If I was to do it again, I'd dig the trench a foot wide roughly level,  and then fill with some hardcore, following that I'd pour self leveling concrete into the trench and let it dry.. Using slabs seemed like a good idea, but it was a hell of a lot of work! I did ask a few builders/paving firms how much it would cost just to lay the slabs, worked out about 500+ hence why I did it myself. I grow everything in big pots in the greenhouse, easier to change soil if there is a problem.

  • I would use the paving slabs for the path for you. A dwarf wall of on edge concrete walling blocks, or bricks if you prefer, would increase the head height and volume (growing space) of your greenhouse. You could use pressure treated timber, or sleepers, instead if you accept a shorter life. A completely solid floor inside has something to recommend it giving freedom from slugs, snails, worms etc. and can keep the humidity down in winter, but I would use very coarse sand. It drains well, it will wick away excess water from pots by proper contact with the compost in the pots, something gravel does very poorly. If you want to grow plants in the ground then you treat it like the garden, accepting it may need refreshing from time to time, or treating for bugs or diseases. Grow bags or large pots or raised beds, on a concrete base sort of give you the best (or worst?) of both systems.

  • I have a 2.2m x 4.4m green house and I would recommend pouring a single concrete base exactly the same size as your green house so you don't get a ledge whihc can let in damp through standing water, expecially important as you are going for wooden frame.It is a fair bit of work but it is easy enough to do, dig out at least 20cm and fill with hard core. Get your wooden frame set up to pour a base at least 15cm deep. Hire a cement mixer, get a couple of big strong mates round, and  mix and pour the concrete base.

    Open soil nees replacing, you will get diseases, damp and fungal problems which are hard to eradicate. A concrete based GH is easy to keep clean and didiease free. Use big Square pots so you maximise space.


    Good luck! 


  • Thanks for all the advice.

    In the end i managed to source some reclaimed council slab for a couple of quid each, so as per the green house manufacturers advice i layed these on a dry mix of sand/cement. I decided against leaving open earth inside the greenhouse and will just pot everything inside, to try and avoid disease/slugs  a bit. 

    The green house has been up a couple of weeks and i'm already enjoying having it image I've started off with mu hardy annual flower seeds already. So plenty going on in there, veg will get module sown this week like carrots, lettuce beetroot etc. image

  • Matty2Matty2 Posts: 4,820

    I have a  concrete block which was laid at same time as house extension went up (buildrs didit as a favour). My GH is 8ft x 6ft, It was my choice but I think I shouls have had some sort of soakaway grid down the middle. The block is about a foot wider with about 2 - 2ft 6ins plinth at the front that enables me to easily put pots in and out and gives me somewhere to sit in warmer weather (well that's the idea)

    In my previous house I inherited and ancient one which was on fence posts, with slabs down middle. I did not find that arrangement at all suitable when you put in growbags and pots etc. It made movement around very difficult

  • figratfigrat Posts: 1,619

    I had a concreted area already, so the 8'x6' gh went on that. With the help of a friend, we put  fresh concrete down to bed the base in, and drilled a couple of holes on the base near floor level so that excess water could drain out. We used the same system when I put up another 4'x2' lean to next to it.

    I have staging in there, but have moved one section outside - it's very useful to have a spare potting area! I use those long gravel trays in both greenhouses, and find it's a great way to keep big pots of toms, cucumbers etc watered.

  • We have a concrete base on our greenhouse 6' x 4' but have plastic floor tiles on top to allow draingage underneath, plus they look better than grey concrete. We got them at  I must say I am really pleased with them

  • I am buying a 8x6 greenhouse in a week or so  do i realy need to buy the greenhouse base  or can i fix it to concrete slabs

  • I have a soil base in one of my greenhouses but I rarely grow anything direct into it.

    I buy reusable woven plastic supermarket bags, 42cm x 20cm x 30cm and fill them with a mix os soil and compost.  Then when they season is over I tip the contents onto the flower beds and start again with frest next year.

    I've found concrete/slabs to be too hot in the summer and harbour slugs underneath them.  With a soil floor the excess water drains away.

  • I have just purchased a 6x6 Pelram Harmony Greenhouse. I thought long and hard about how to do the base as I was building on uneven grass. I came up with an idea that I had seen used before and that is to forget about the ground for the moment as that would take too long to level out. Instead I purchased some M10 studding and some M10 nuts along with a bag of post fix cement. I will cut the studding into 12 inch lengths and put a but on the end and cement them in place.So now I have threaded posts in the ground. I fix a M10 but to each post and lay the base on top. I then adjust each but until the base is level. I then put a locking nut on top to hold the base in place. Then build the greenhouse that is now secure and level and any alterations to the ground can be done after to tidy up and make good.

  • LynLyn Posts: 8,059

    Sounds good but I have no idea what m10 studding is!

    Gardening on the wild, windy west side of Dartmoor. 
  • hogweedhogweed Central ScotlandPosts: 2,477

    My greenhouse sits on a concrete slab. No gaps for weeds/seeds to germinate and easy to keep clean and swept.

    'Optimism is the faith that leads to achievement' - Helen Keller
  • M10 studding is threaded rod that you can get from B and Q and they also do the m10 nuts.

  • HamHam Posts: 1

    I will be putting up an aluminium 8' x 6' GH with a solid concrete base. How do I ensure proper drainage? I've heard of a 'sponge like' material that can be placed between the frame and the concrete to allow drainage. Any help appreciated.

  • Trench dug the area of the greenhouse. Block on its side around the footing. timber shims at either side of screw hole to level it then the gap mortared up. Soiled up to the blocks inside and out paving slabs laid on top of soil at each side in the greenhouse and central passageway sunk below that.

    That's not a recommendation:

    Timber shims rot.

    The soil settles so

    Blocks at footing move,, gastropods get in by the dozen 

    Slabs are off level making all the staiging off level making watering into trays uneven resulting in a a disproportionate number of infant mortalities .Nothing is plumb square or level. I didnt install it.

    The hardstanding (reclaimed bricks) around the greenhouse is nowhere near flat and  a far from ideal surface to work off steps with glass panels and fiddle clips

    Once it's installed it's always much more of a faff, more expensive and more labour-intensive effecting repairs and sorting things out than doing a good job in the first place in a vacant space.

    When I come to replace the greenhouse with a bigger one duct in utilities then get some concrete guys to vibrate in MOT1 then shutter in poured concrete.  I'll fabricate a base to give 2degress runoff for rainwater if that is not designed into the guttering or the guttering angle is not adjusable.

    One feature I'll use again is storage heater bricks for the central passageway for thermal mass to stabilise the day/night temperatures. 

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