I am a member of the Rio Grande Community Farm in Albuquerque, New Mexico. We have a new greenhouse this year and want to operate it organically.
One issue that is pressing at the moment is the type of flooring we install. We want to get this right the first time of course. One suggestion was a layer of crushed gravel. Onother suggestion was bark mulch. Information from individual with experience and the pros and cons of flooring options would be very much appreciated.

Also, information on operating an organic greenhouse in general, reference materials and resources would also be very helpful.

Thanks

Hi, Moonbow and welcome to OG.

I can offer a suggestion for the flooring, having had a greenhouse (except for last year) for a number of years. After leveling the ground (of course) we laid porous weed cloth. Not black plastic - even the kind w/the holes - but a fabric weed barrier. After trying a number of different elements to cover that, we ultimately opted for pea gravel. Nice and small, felt good underfoot and provided great drainage. The drainage being the key. I suppose any other kind of small crushed stone would be fine.

I'm sure there are loads of resource material through a good Googling that could provide a lot of information on running a full-scale organic greenhouse operation.

This one from ATTRA on Organic Greenhouse Vegetable Production may be of particular interest.

Good luck.

Yes, welcome to OG.

We run organic greenhouses, and the keys here are:

(1) an absolutely weedproof fabric. Weeds can go crazy in a greenhouse environment, so take no chances. My favorite (and others') is black, woven polypropylene available at about 6 cents a square foot from greenhouse suppliers. It's foolproof.

(2) For covering that, use whatever is comfortable to walk on. What they call "crusher-run" gravel is my favorite because it packs down and is comfortable to walk on. If you use pea gravel don't make it too deep lest if shift underfood, making it hard to walk.

We use compost tea and worm juice from our vermicompost bins to feed seedlings. If you want organic certification, you'll have to make your own potting mix because the wetting agents in commercial mixes are a big no-no, and I've yet to find OMRI-listed organic potting soils that are worth more than warm spit. Peat, vermculite and compost make a nice mix.

Incidentally, the state inspector once told us it was impossible to run a greenhouse without fungicides and pesticides, and I said "Watch me." He called a few months later to see how we did our first season. I told him we raised about 13,000 seedlings.

"And how many did you lose to pests and diseases,"asked he.

"Six," said I. "I think we'll do better next year."

Good luck!

Oops, almost forgot. You'll find very little of any use on the Internet. I know a fellow who just wrote a book on organic farming,however, due out next March, with a chapter on greenhouse, so if you send your email address to pfossel@thehermitage.com, I'll send you the chapter.

Peter,

Are you the General's gardener?

This is Peter's forté, so I'd heed the words from the horse's mouth on this that there's not a lot (if any) useable info out there on the Internet.

Speaking of heeding your words, Peter...I've never seen (or heard of) "crusher gravel". Doesn't sound like something any Big Box would carry so I'm assuming it can only be found at stone/gravel yards, am I right? Since I'm in the market for a new greenhouse and I've since found other uses for that pea gravel, I'd like to investigate the crusher gravel. Thanks for any direction on this.

Well, thanks for your confidence. Truth is, I just muddle along trying to get things right. "Crusher run" gravel is also known as "bank run" some places. It's comprised of crushed gravel together with stone dust, which, when spread out, moistened, and packed underfoot, becomes quite solid and foot-friendly. Indeed you must order it from a quarry. Tell them the square footage and how deep you want (1-2 inches is good) and they'll calculate how many cu. yds. you need.

George, yes, the general's gardener. What a pleasure.

Peter,

My mother lived in Nashville during the war (WWII). I visited the General's house about 20 years ago, and enjoyed it muchly. Please give him my regards.

As you may know, I'm fairly new to this forum, but understand that you are in the final stages of writing a book. Other than that, I have no info. Please let me know more about that project.

Peter, isn't it tragic when people just assume that chemicals are the only things that work? The State people have college educations and they still rarely look beyond the nonorganic ways of doing things. I do remember you saying this last spring how well your teas had done, and I hope your success spreads far and wide!

gardenz, that crusher gravel is the stuff they use on dirt driveways, and where I am they call it Grade II road gravel. But the word to use when asking for it is "compactable" road gravel. The contents of it reflect the local rocks. Where I am it's granite and local clays. I imagine they have all kinds of names for it. I can go to the rockery and shovel my own, it's extremely cheap.

Around here they call the crushed rock by it's size. 1/2" minus is 1/2" inch and smaller. It has lots of fine stuff and packs well. Easiest to walk on. Next size up is 3/4" minus. Slightly larger with less fine particles. Better for driveways.

I have a question. You said that you are running an "organic greenhouse". Are you running a "solar powered" greenhouse (i.e., no outside heat source)? If so, I would recommend a conrecrete floor (painted either black or dark green) as a thermal mass. That way you wouldn't need any extra (read, expensive) heaters for the greenhouse. You might also look into insulating 3 sides and the top (as you would only need glass on the south side to let the winter sun in). Finally you might want some (prfereably black painted) water filled barrels as but a thermal mass and a source of humidity in the greenhouse.

Now watch the comments fly.

These are sound ideas, espoused by many during the energy crisis 25 years ago (see The Solar Greenhouse Book, James McCullagh, 1978). The problem with insulating three sides, however, is that the south side, with an R-value of 1 or 2 (at the most)loses enough heat at night to more than offset any gains from insulation on the north wall. That is, unless the south wall is also insulated at night (see Thermal Shutters and Shades, W. A. Shurecliff, 1980). This soon makes for a very expensive greenhouse.

As for heat gain from a thermal mass or heat sink, such as a black concrete floor or water-filled drums, these do indeed absorb solar radiation by day and return it as heat by night. BUT, the sun must shine directly on them during its low arc in the winter sky, and any space given over to solar storage is lost to plants (see Keeping Warm, Peter Fossel, 1984).

In a nutshell, you can have a heated greenhouse for raising plants, an unheated house for raising cool-weather crops (see The Four-Season Harvest, Eliot Coleman, 1994). Or you can have a costly passive solar greenhouse that doesn't have enough space or heat from growing much at all. It's one of those "no free lunch" things.

Does the climate or latitude have anything to do with it? Is there any point trying to supplement "bought" heat with solar power? I assume that in my climate, a person would have to heat a greenhouse in order to have much benefit at all in the winter.

While it is true, Pete, that there is no free lunch, it is not true that the sun has to shine directly on ALL the thermal mass in order for it to be effective.

For instance, if the insulated roof of the greenhouse slopes toward the south side and the north side is stocked (floor to ceiling) with black painted 55-gallon drums filled with water, normal convection currents in the water heat it to the tops of the barrels. Even when only the bottom half see any direct sunlight. The process of this convection current allows more of the barrel to store heat and make it all useable as a passive heat source at night.

Also, the "shutters you mentioned need be no more than heavy curtains to be of use. While they won't be as effective as insulated shutters, they will slow down the heat loss.

As for HAVING to have a heat source to grow anything but cool weather plants, you might be right, but a proper design and heat storage system can minimize the expense needed to make the greenhouse work.

My neighbors have been running a small commercial greenhouse for some time now (they closed it last year do to not being able to keep paying the workers - and the family wanted to drop the extra work), but they only needed to heat the place for 10 days over the last 5 years due to a good design and a good heat storage system.