Organic Farmer Network: Network Discussion Summary

Topic: Greenhouses

Mark tells about growing flowers in the greenhouse: “Although we've been reading about the hoophouses for several years now, it has been our experience in the heated greenhouse that had us itching to have more space. One half of our big greenhouse is on-the-floor growing beds, created on top of the landscape fabric with 1" by 10" cedar boards pinned into place with rebar pins and filled with topsoil. We have grown lisianthus, 'cheerfulness' stocks, 'Potomac' snapdragons, salad greens, celosia, and zinnias in these beds. WOW! Our first crop of lisianthus several years ago, planted March 1, flowered at 3' tall in mid-June, gorgeous; stocks planted from seed in early October and transplanted to the beds in early November bloom for our first markets in early April, and mix well with tulips and daffodils from outdoors; snaps planted on the same time schedule as stocks bloomed for us in early May, giving us a huge amount of blooms for Mother's Day. Last year we grew crops for fall in these beds--we planted Chief celosia in late July in flats and transplanted to the beds in August, with incredible stems by late September, and did the same with zinnias. Although the zinnias were useful to mix with our late outdoor lilies, they got a bad case of powdery mildew and were pretty leggy. Celosia loves the heat! And it is very hot in there--midsummer temps are often 120 degrees in there even with the big fan on, no shade cloth, no roll-up sides. For these over-wintering crops of cuts, we do not heat the house unless we feel indoor temperatures will fall below the mid-teens inside: all the crops are covered with row-cover as well.

But now, since we are beginning to sow the first rudbeckias, etc, we will be heating the greenhouse (ours is wood heated) and try to keep evening temps at 50 degrees minimum. This often requires me sleeping up there to load wood at about 2 a.m. Builds character!!”

Paul has problems with slugs and mice in greenhouse: “Every year at this time [late February] we experience major problems with slugs and mice in our greenhouse. We set baited slug traps and many mice traps, which help to some extent, but are not 100% (or anywhere close to!) effective. I find baiting the mousetraps with squash or melon seed works well. What do you use and what have you found to be the most effective?”

Ken replies: “Our seeding flats are up on benches ( I use 55 gallon drums full of water for bench legs) and we have never had a problem with slugs. Mice occasionally, I use regular old mousetraps and peanut butter, with good success, but they sure can hurt you quick if you don't get rid of them (mice, not the traps)”

Paul talks about germination mats: “We also use germination mats in our greenhouse. They work really well. We leave the greenhouse cool, about 50- 53 degrees, and set the temperature on the mats to most effective germination temperature for the majority of the crops we are seeding at that time. We have four 8' by 22" mats, and we can put 9 flats (1020 size) on a mat. We leave them on long enough to get good germination, then move them off onto other benching and put other flats on the mats to get the seeds up and growing. This system works really well for us. We've had the mats since 1993 and have never had to replace them so far!”

Ellen has to replace snow damaged greenhouse and touts Atlas greenhouse supplier “Atlas has been a dream to deal with - wonderfully kind helpful people, a great product, and good prices. Bought another 24x96 house from Atlas, arriving this week,(paid on Friday, shipped on Tuesday!!!!) and so we need to demolish the flattened greenhouse and rebuild in the same place. The site has had a gh for 16 years, once had plastic with gravel on top, and now the weeds sure come through the floor… I've ordered ground cover and am considering just covering the whole mess, including the gravel, and either adding new gravel on top, or just walking on the ground cover. Any ideas?”

Ken responds: “I have landscape fabric on top of gravel. That way we can sweep it out periodically and don't have soil mix and tracked in dirt filling up the gravel and growing weeds. Have had the same fabric down for 8 years and it's doing fine.

Mark responds: “Our large greenhouse also has the fabric on top of gravel. Jay Fulbright suggested this when we were building it, since he has spent so much money in labor hours weeding his gravel-over-fabric houses. (And he has lots of houses). I'm pretty happy with being able to sweep the floor, no weeds. Hopefully the fabric will wear well--this will be our 5th season in this one.”

Ellen asks about using pressure-treated lumber in greenhouses and bench construction.

Ken responds: “It is my understanding that the treated wood in greenhouses issue applies to new construction. If they are going to require us to take out old stuff, I haven't been informed of it. I haven't built any benches in several years, don't anticipate doing so as I have enough and am not expanding in that way, my old ones are treated. (BTW- I used all metal framing in the new house I just put up, primarily because of the treated wood issue.) There is a new treated lumber on the market called ACQ. It has no arsenic or chromium, the 2 blacklisted treatments. I asked Marty and Amelia [from Quality Certification Services] about it… Marty said probably OK. Amelia said not sure, wait and see. The way my benches are built, they have welded wire on top of the framing so there is no actual contact between plants or flats and the wood. Doesn't look like an issue to me, but we know what we are dealing with here- the guvment, so who knows.”

Cathy responds: “Pressure treated lumber - I checked at my local lumber yard yesterday and they said that Cox Lumber makes the "new- non-toxic" PT lumber. They said it runs 20-30% more in cost. It's called Natural Select. They suggested that you do a search for CoxLumber.com”

Paul responds: “We have some benching with welded wire on it. Benches are 6-foot long with 1 cross piece. After 10 years, it's really sagging and makes for very uneven watering. We also have benching with snow fencing on it. I believe the fencing is made out of cedar. Really rot resistant and is holding up really well after 11 or 12 years.

I tried getting the new pressure treated lumber here. None of the lumber yards (I went to 5 in both Glasgow and Bowling Green) are carrying it. They all told me that they couldn't get it until supplies of pt lumber had been used up. Some companies are using a type of poly lumber for fencing. Looks good and durable. That might be a good alternative. Our understanding is that these requirements only apply to new construction.”

Mark responds: “An added note to a previous discussion about greenhouse benches: we used galvanized metal pipe pieces that were pounded into the ground though the landscape fabric, with the same type of pipe bolted to the uprights horizontally to hold up 'hog panel' that serves as the bench. If you need to support a lot of pots, the metal hog panel may not be appropriate because the openings are a bit wide, but for flats it works well. An added advantage for us is that we have created growing boxes below the benches that can be used after the main spring propagation period, and the hog panel acts as floral netting. We grew dynamite celosias, lisianthus, and zinnias this way late last season in a very hot greenhouse, making use of otherwise wasted space. I think it's possible we're seeing no mice problems because of the pipe bench supports.”

Paul tells about erecting a new greenhouse in the winter: “We've been trying to erect a new greenhouse and working in the mud is exhausting. We were able to get 1 layer of poly over the bows this week. It took a whole day just getting ready to put the poly on. First I laid ground cloth on the West side and hauled in gravel so that we wouldn't be standing and kneeling in 3"of water. Then I hauled wheelbarrows full of gravel down to the front of the greenhouse so that we could carry the poly to it. Then I laid out boards so we could walk with out sinking in to our knees in mud. Then I laid out 10' wide ground cloth so that we could roll out the poly without getting it covered with mud. Then I laid down boards and ground cloth from side to side so that we could walk around the structure. And anytime you stepped off into the mud you instantly sank in. Alison had left early for work so that she could leave early to help put the poly on. Just before she got home at 3 PM, it started to mist.

I had brought the poly into the house so that it would warm up and be easier to handle. We unrolled it and cut it to size in our front yard where there is still grass and no mud. Then we loaded it in the pickup truck and drove as close as we could to the greenhouse. Then the fun started! We have put poly on 20 x 96-foot hoophouses by ourselves more than once, so we thought we could handle a 30 x 48. HAHAHA! The light mist on the bows and poly acted like glue. We pulled and pulled and pulled and finally pulled the poly up and over about 75 percent of the way and it wasn't going any further when a breeze came out of the north east, picked up most of the poly and dropped it back down almost exactly where we needed it! Then it was a race to attach it in a few places with some wiggle wire before the wind decided to blow it into the next county!

Before we started erecting the greenhouse, we had a dozer in to excavate the pad that the greenhouse is on. We wound up doing more fill on the northwest end and more excavating on the southeast side. So the ground on the NW is pretty loosie-goosie, if you know what I mean! I had put down 4 x 8 sheets of plywood on the South end so that Alison could climb up and attach the poly. (I know better than to be up on a step-ladder in these conditions!) And I had this GREAT idea that I could drive the IH 784 and she could ride the bucket and attach the poly on the north end. Being the slick talker that I am (and having 51% say in our household), it was easy to convince her that this was a good idea.

I am sure that the ruts the tires made will come in handy some day. Perhaps we can bring in a laser level and grade for a rice paddy and use the ruts for flood irrigation. Or if we are attacked and can't fend them off with duct tape, we can use them as anti-tank ditches. Or perhaps we can turn this into an agri-tourism non-farm, seed them with cubic-zirconium and convince people this is a diamond mine!!! The possibilities are endless, and with the snow we had last night on top of all this mud, I'll be able to spend the day thinking of the many different things I can do with them.”

Ellen shares their story of erecting their replacement greenhouse, written by Hana Newcomb, her farm partner: Click Here for Hana's Greenhouse Raising Story

Rosie and Tom tell their greenhouse construction story: “Our last greenhouse install (also Atlas, a hoop) was scary. We've got tomatoes in the field in late September for winter season, plan is to put the greenhouse up after having planted, since we're so organized you know. Early freeze warning comes out, so the greenhouse has to get up that afternoon or byebye Sungolds (I think we had the short stake poles and the layout done already). We got the hoops up and had one side of plastic up (not the lee side) and the front came in with about 35 mph and literally a 25 degree drop in temp and blew the plastic to the other side for us. We (about 5 of us) scrambled to the other side to catch the plastic before it took off and just huddled about 20 feet apart while the cold rain came down and the wind blew. We couldn't let go to get the wood, nails and hammers so we just kind of held on and shivered. The image that came to mind of more than one of us was that if the wind picked up anymore, the plastic would go horizontal with us hanging on; it wasn't too far from it. Finally, after about 10 minutes it let up and the rain petered out. We finished up the side and the help left, leaving us to finish the ends in the dark.

Without the excitement, they're pretty easy to put up.

Ellen wants to know about fertilizing in greenhouses: “Do you fertilize in the greenhouse, with what and how? I've only been using fish/seaweed mix from Johnny's put through watering hoses using Syphnex - imperfect at best.”

Nicolas responds: “I don't have much experience with greenhouse growing other than this year. I added lots of compost with kelp meal, green sand and gypsum. It seemed to be working fine. I am already seeding my 3rd crop of arugula since December 2002.”

Ken responds: “What to put in the mix and how to fertilize has been an ongoing exploration for years. I use a peat, vermiculite, perlite mix and add various amendments before filling trays and if I get it right, I don't need to do any thing else. My experience with fish/seaweed fertilization has been inconsistent, sometimes effective, sometimes it seems to have no effect and plants just stop. We all know tough little plants do well when they go to the field, but when you are selling them, folks want them green. This year I am mixing in about 20% worm castings of rabbit manure origin, plus feather meal (13% N), ashes, and granular kelp. Things are growing great, but a bit too lush, so I have cut back on the feather meal. Earlier, I was using a double handful of feather meal per 3 cu ft bag soil mix, plus 5 gal bucket of worm castings. Have cut back to single handful of feather meal, will be a couple weeks before I can tell if that is enough N. You make good compost, I would think if you save some for an extra year, let it get really aged, but not leached, and used it at about 20% or so, that would be all you need, forget the fish emulsion.”

Cathy responds: “We use the same potting soil that Ken does, Fafard #2 potting mix which they make up for us without the starter solution and the wetting agent (certification no-no's). Over the years we have settled on a couple of additions to boost the mix- we add worm castings (enough to make up 10% of the volume), 2 cups of rock phosphate (even though I don't see how it would have any effect) and 1 cup of blood meal. The blood meal has proven to be enough to really make a difference in health of transplants. Crops like onions/ leeks that stay in the greenhouse for a longer time might get a soak mid-term in a solution of fish-emulsion and water ( 1/2cup fish per 3 gallons of H20). I have a large sink that I keep this mixed up in, because right before I go to the field with our transplants, they get soaked in the same solution. I figure one last heavy drink will carry the plants through any transplant shock. I don't know if it is excessive, but it seems to work for us.”

Charlie responds: “I make up most of the potting mix with the following formula: To a 30 quart bag of Fafard mix (just peat moss and perlite) I add 10 quarts compost, 1 1/2 cups of equal amounts of blood meal, rock phosphate, and greensand mixed together, and 1/4 cup lime. This is usually enough fertility to carry the plants to the transplant stage, but if more is needed I will foliar feed with "Sea-Plus," a fish emulsion and seaweed mixture… The NPK is 3-2-2... I use the "Sea-Plus" religiously to water in when transplanting. A good source for the "Sea-Plus" is Pinetree -- $21.95 a gallon including shipping.”

Cathy adds: “I have been using "Alaska Fish Emulsion" for the last few years with a N value of 5%. We soak flats of plants in a solution made of 1/2 cup of Alaska for three gallons of water, just before transplanting.”

Nicolas adds: “I also soak my transplant in fish emulsion. I combine Fertrell #1 and #3. #1 is 4--1-1 and #3 is liquid kelp.”

Marks questions producing hanging baskets in greenhouse: “Something we've experimented with several times now that I'm not at all sure is worth it is hanging baskets...I always like having that layer of plants up where nothing else is growing in the greenhouse, especially for the color, but the profit margin is slim and hauling them to market takes too much room! We're slowly selling off the zonal and ivy geraniums and impatiens baskets at each market. I was particularly happy to find attractive biodegradeable baskets from Hummert's in St. Louis--plastic pots are YUCKY. However, we are trying to simply make $10 over expenses with the baskets, and it's a slow selling item. When you can take in almost $1400 on a Saturday morning from greenhouse snaps, sweet williams, and a few lilies, hauling baskets around seems like too much trouble. Any ideas out there for using vertical space in the greenhouse?

Speaking of which, the growing beds beneath our greenhouse benches are being planted to celosias as the benches are emptied; the early stocks replaced with sunflowers for bouquets on a 5-row, 2" in-row spacing. How are the rest of you using your greenhouse/hoophouse spaces for the summer?”

Alison responds: “We agree with the problem of transporting baskets. Is there some way to rig some conduit in your transport vehicle so they can hang there like in the greenhouse? Taking up vertical space rather than shelf/floor space? We are only doing wave petunia baskets, have sold out once, but potted up some more last week.”

Tim wants to know about the type greenhouse Cathy uses.

Cathy responds: “Michael and I designed and built the greenhouse. The basic design came from an old (1978) Rodale Press - The Solar Greenhouse Book by James C. McCullagh. The white portion is Hebel Block (lightweight, high R value, aerated concrete) the rest is framed with yellowpine from a local saw mill. The windows were recycled sliding glass door panels. I don't see why the design couldn't be expanded - you might need some center support post (???) Try to find the book first, real good info on Passive solar stuff.”

Ken adds: “Ditto Cathy's recommendation on the book. My first greenhouse, built in 1985 was a similar design, using the same book as a reference. Performed well from a heat collection standpoint, temp never went below 38 when 5 degrees outside, (would probably have heated my house had it been connected) but I was not pleased with the light admittance for plant growth. That and the high cost per square ft for construction led me to choose plastic covered quonset type structures for subsequent houses. If you do choose to build this type structure it could be adapted to any size you want. I have seen similar built at about 60x150 ft.”

Charlie needs greenhouse heater advice: “I am considering getting a new greenhouse heater, and would appreciate some advice. This is for my small 10 by 16 greenhouse where I do my starts. I have been using a kerosene heater, like the ones you use Rosie, but I would like to switch to something else that doesn't have the fumes. In years past, I have turned the kerosene one on only when I am not in the greenhouse, usually at night when temps get low. But this year, I am going to expand my seedling and transplant production, and need something to give a more even heat, and something I would rather be around. Are there heaters any of you are using that you would recommend?”

Ken responds: “ http://www.littlegreenhouse.com/accessory/heaters2.shtml
The above site is the greenhouse division of Aarons Creek Farms, a large nursery operation in Southside Va. They sell electric and gas heaters. On the site is a calculater to help figure the BTU's needed to keep any size greenhouse any number of degrees above outside temp. Most folks use gas heaters in greenhouses. Modine is a very common and well thought of heater brand. Your size greenhouse would use a very small gas heater. To give you a rough ballpark, my transplant house is 28X45, double poly covered. My heater is 125,000 BTU's rated to keep the inside temp up to 50 degrees above outside. Think about the minimum inside temp you want and a worst case scenario of how could it might get at the time of year you want that minimum temp. Gas is probably cheaper in the long run than heating with electricity, though more expensive to set it up. You will like having a system set up and a thermostat to control it.”