Solarization of our whole hoophouse

 

Solarization plastic spread across our hoophouse. Next we weighted down the edges with small buckets of rocks. Photo Ken Bezilla

I wrote in August 2019 about Solarization and Crop Choices to Fight Nematodes. Previously we solarized part of a bed in our hoophouse, or one or two beds. I’ve written before about our first efforts at solarization to fight root knot nematodes in our hoophouse. Back then we shoveled soil on the plastic edges to make a good seal between the plastic and the soil. Later we developed a good technique of pushing the plastic edges down into soil using spades, which gives a much better seal, and if you work both sides of the bed at the same time you can avoid wrinkles.

Solarizing a single bed in 2019 using a spade to push the plastic edge into the soil..
Photo Pam Dawling

This summer we decided to solarize the whole hoophouse. We hope to make progress on reducing fungal diseases in our winter crops, drawing down the weed seed bank, and killing lots of nematodes. We plan to solarize for the whole of August (4 weeks). Here’s the story so far.

Solarization

Solarization is a method of killing pests, diseases and weed seeds near the surface of the soil by covering the soil with clear plastic in hot weather. Nematodes are only active in warm weather, and we have not had problems with them outdoors, but of course, it’s warmer in the hoophouse!

In my Book Review: The Organic No-Till Farming Revolution: High Production Methods for Small-Scale Farmers, Andrew Mefferd, I wrote a little about solarizing:

“Solarization uses clear plastic (old hoophouse plastic is ideal). In a summer hoophouse, solarization can be as quick as 24 hours, Andrew says. When we’ve done this, one of our goals was to kill nematodes and fungal diseases, not just weeds, so we waited a few weeks. Outdoors it takes several weeks. You can see when the weeds are dead. Bryan O’Hara poked a thermometer probe through solarization plastic and found a 50F degree (28C) difference between the outside air and the soil immediately under the plastic; a 10F (6C) difference at 1″(2.5 cm) deep and little temperature gain lower than that. Solarization does not kill all the soil life!”

Preparation for Solarizing

Last time we changed the plastic, we saved our old hoophouse plastic in one large sheet, for just this option of solarizing the whole hoophouse. Unfortunately, someone used it for some other purpose, and we ended up having to buy new plastic to carry out our plan. Ouch! Label your old plastic very thoroughly! We bought 4 mil Tufflite Nursery Clear plastic from Nolts Greenhouse Supplies, Ephrata, PA (only rated for one year outdoors), thinner than the 6mil we buy for covering the frame. Be aware that shipping can be a big part of the cost, unless you are ordering lots of things.

Clearing hoophouse tomatoes and sunn hemp cover crop.
Photo Pam Dawling

We pulled up our tomatoes and cucumbers at the end of July, a week earlier than usual. The squash had already gone. I was sad to say goodbye to the bell peppers as they were the best we’ve had in years. Usually we keep the peppers until October and do our winter crop planning so that the pepper area is the last planted in winter crops, but we made that sacrifice! For several years our peppers didn’t do well, as the salinity of our soil had got too high. We now do salt wash-downs in September and March. This year they were spectacular! Big plants, huge peppers!

Lady Bell peppers ripening on 7 July.
Photo Pam Dawling

We decided to keep the big shadecloth in place for the solarizing day, expecting it to be very hot. It wasn’t, but it was a wise precaution. We planned to remove the shadecloth the next day, but it was raining and we need the shadecloth to be dry to pack it away. So we waited a couple of days for our little monsoon season to pass. Normally we leave the shadecloth in place until mid-September or so, but this year we want maximum heating for the solarization.

We are leaving the drip tape in place so we can water the soil and keep it alive below the hot zone. If we had thought of it in time, we might have spread compost on the beds before spreading the plastic and killed the weed seeds that have landed on the compost pile while we ignored it since early April. We were stretched thin and got behind with the mowing, and we know grass and spiny amaranth seeded somewhat on to the pile. We did have it partly covered with a tarp.

Unrolling the Plastic

Unrolling plastic to solarize the hoophouse.
Photo Pam Dawling

We bought plastic 32’x100’ which was just right for the footprint of our 30’x 96’ gothic hoophouse. We unrolled it down the center bed (it was folded in several concertina folds from each edge to the middle). We gradually unpacked the folds and pulled the plastic out to the edges. It is important to get as smooth and tight a fit as possible (few airgaps between soil and plastic).

We designated one person to take their sandals off and walk on top of the plastic, while the rest of us gathered small buckets and put some rocks in them, to anchor the edges. This all went very smoothly and took less time than we expected. We used about one bucket of rocks every 20’ down the length. We rolled our painters’ pole that we use for our SnoBrum in the plastic across the west doorway, the direction the strongest winds come from, for add extra security in preventing wind getting under that edge of the plastic. We did not bury the plastic edges in the soil, as that seemed difficult and we figured a large area would suffer less edge cooling/heat escape than a single bed.

Closing Up the Hoophouse for a Month

We closed the doors and windows and relaxed into enjoying a summer month off from harvesting in the hoophouse. We have made a list of infrastructure repairs, landscape care and, of course, the winter crop planning to do in t he next month. And we’ll be irrigating maybe twice a week and checking the soil thermometer periodically. It showed 80F last week, before we solarized.

Hoophouse solarization at Dripping Springs Garden, Arkansas.
Photo Pam Dawling

More Resources on Solarizing

eOrganic’s Organic Vegetable Production Systems Topics list offers publications on plant disease management, weed management and management of soil-borne pathogens using Anaerobic Soil Disinfestation. Here’s a 2025 webinar about On-farm Anaerobic Soil Disinfestation for the Management of Soilborne Pathogens in High Tunnel Production Systems:

 

https://www.youtube.com/watch?v=2pEf26ae6XI

The University of California Solarization site and their Small and Organic Farm Advisor have good information, including some in Spanish and Hmong

More Resources on Nematodes

I’ve written here before about our struggles with root knot nematodes in our hoophouse, and you can read everything I know about nematodes in the Year-Round Hoophouse.

My article on nematodes in Growing for Market  in November 2014 describes our discovery of the beasties and our first attempts to deal with them. My most thorough blogpost about nematodes was for Mother Earth News  Managing Nematodes in the Hoophouse. It’s free for MEN members.

There is info on dealing with nematodes from Garry Ross in Hawaii, where nematodes are a fact of daily life, in my post Cold weather, snow, thinking about nematodes from February 2015.

Planting winter hoophouse crops

Our first hoophouse radishes germinated three days after sowing. We sowed Cherry Belle and White Icicle. We would have sowed Easter Egg if we’d had enough seed left after the outdoor fall sowings.
Photo Pam Dawling

We’ve already prepared our first bed in the hoophouse and sowed our first few crops (spinach, radishes, scallions, tatsoi, Bulls Blood beets and cress). We spread the bed prep out over 5 days and the sowings over 2 days. I’ve written lots about our fall hoophouse planting, so I’ll give you links, mention a few updates and stick to photos otherwise.

Mid-October photo of September-sown tatsoi and August-sown Tokyo bekana. Fast-growing crops make good use of small windows of time.
Photo Pam Dawling
  • Hoophouse Winter Schedule Tweaks and Improvements (pack more crops in, get higher yields, reduce or spread the workload). One change we made was to sow some early catch crops in areas that weren’t needed for all-winter crops until later. We mostly used tatsoi and Tokyo bekana, both fast–growing leafy greens. We intended to grow some early beets too, but the seed didn’t germinate. A new crop last winter was cress, Creasy Greens Upland Cress and Belle Isle Upland Cress from Southern Exposure. They take 50 days to maturity (in spring). We had two good intentions we did not manage to follow through on. One was to let some of the cress flower, to feed beneficial insects. And I think we got too impatient. The other was to notice which one of the two kinds we prefer and just grow that one. We didn’t manage to keep good enough records on that, so this winter we are obliged to repeat the experiment, with more good intentions!
Belle Isle Upland Cress from Southern Exposure Seed Exchange
  • Using all the space in the winter hoophouse (filler crops for random spaces, fast-growing catch crops, radish sowing dates for seamless harvests.)
  • Fall hoophouse bed prep and shadecloth removal (packing away the giant piece of shadecloth until May, spreading compost, broadforking and raking the beds, direct sowing the first bed, sowing seeds in an outdoor nursery bed to transplant into the hoophouse a few weeks later). This post includes a step-by-step guide to hoophouse fall bed prep. Our soil is improving each year, becoming easier to broadfork and rake. That counters the aging process of our human bodies! One change we made last year was to measure and pin down the drip tapes 12” (30 cm) apart, and use the drip tape as a guide to making furrows (drills). This is easier than using the row marker rake, as we used to do.

    Our hoophouse with shadecloth for growing summer crops. Photo Pam Dawling. We have now sewed the two pieces together, to avoid the gaping hot spot in the middle!
  • Hoophouse fall bed prep (includes an appreciation of spiders and a video of spider “ballooning”)
  • Sowing hoophouse winter crops (more details on bed prep tools and techniques, including the row marker rake if you want to use that, and links to posts about winter lettuce varieties we used in 2017/2018.)
  • Planning and Growing Winter Hoophouse Vegetables (hoophouse crop map, many links to other posts including a video and three slideshows, crop rotations, choosing winter hoophouse crops, posts about specific crops (with all the details), back up plans in case something goes wrong, and harvesting.)

    Mid-October emergency back-up seedlings for the hoophouse.
    Photo Pam Dawling. We needed to compensate for poor germination that year.
  • Preparing your hoophouse for fall and winter (includes one of my slideshows, and a more detailed discussion of lettuce types and sowing dates, information about salt build-up and our wash-down strategy in a 3-slide mini slide show, when we close and open the doors and windows, and a Be-Prepared Winter Kit list)
  • Planning winter hoophouse crops – our step-by-step process for hoophouse crop planning.

    Spinach seedlings (from pre-sprouted seed) emerged on the third day after sowing. here they are on day 4. Photo Pam Dawling
  • Winter hoophouse growing (includes a round-up of earlier posts, and a discussion about the value of crop rotation in the hoophouse, and a list of 20 benefits of having a hoophouse.)
  • Spinach variety trial conclusions This year we are growing Acadia.  Johnny’s do not recommend this variety for late fall or winter sowing, but it did very well in our hoophouse, sown in September, October, November and January.
  • September in the hoophouse: sowing spinach 
Two jars of sprouted spinach seeds and grits to prevent the damp seeds clumping. presprouting spinach seeds for a week in a fridge gets round the impossibility of getting spinach to germinate in hoophouse soil at 80F (27C) as it is September 11.
Photo Pam Dawling
One side of our hoophouse on Sept 10. Three beds with cover crops of buckwheat and sunnhemp (which got bitten down at a young age by Something), and one bed under solarizing plastic in hopes of killing nematodes. Photo Pam Dawling
Zipper spider on the pepper plants in our hoophouse September 10.
Photo Pam Dawling

September in the hoophouse: sowing spinach, replacing bubble foil insulation, removing shadecloth

Two jars of sprouted spinach seeds and grits to prevent the damp seeds clumping.
Photo Pam Dawling

Sowing Spinach

We sow our first hoophouse spinach in the ground around September 7. Because it’s too hot in the hoophouse at this time for spinach seed to germinate, we pre-sprout the seed for a week in the fridge before sowing. This is very easy, much easier than growing beansprouts!

We measure out the amount of seed we’ll need and soak it overnight in a jar of water. We use 1oz (28 g) of seed per 90ft (27.4 m) row. We use a cup measure or a tablespoon that we keep in the spinach seed bucket. 7T = ½ cup. 1T=15 ml. It’s very roughly ½ cup per row. We use Mason jars and replace the flat metal lid with a piece of screen of some kind, metal or plastic, with holes smaller than spinach seeds. The Mason jar lid band holds this in place.

In the morning we drain off the excess water, and set the jar in the fridge on its side. Once a day we rotate the jar to even out the moisture and therefore hopefully the rate of growth of the shoots. After about a week the seeds have grown a short white root 1/8” (3 mm) long and are ready to sow.

Spinach seedlings from pre-sprouted seed in the hoophouse in September.
Photo Pam Dawling

When there is extra moisture with the seeds they can tend to clump together. One solution to this problem is to mix in a dry inert material like corn grits, as in the first photo, to make the seeds easier to sow individually. This year I tried a different approach. I spread out a scrap of rowcover on the ground and spread the seeds out on that to dry the surfaces. This made the seeds easy to sow, but I noticed that several white rootlets were left behind on the rowcover. I don’t know if the rowcover Velcro effect caused this or if it was a higher rate of damage than the grits treatment. It wasn’t a significant amount.

Replacing bubble foil

Beyond time to replace this torn and crumbling bubble foil insulation.
Photo Pam Dawling

We have a 3 ft (1 m) length of a foil and bubble-plastic roll material along the base of the north wall in our hoophouse. The north side is the coldest, and not a lot of direct light comes in there, that low down, so we decided to insulate from radiation losses and also get some light reflection back there. I think it works well, although I have not measured anything to see if my impressions are backed up by reality! We put the hoophouse up in 2003 and we have replaced this “bubble foil” once since. Definitely we left it too long since we last changed it. As well as big rips, we had micro-crumbs of plastic flaking off. Not what we want in our food!!

An office staple remover is the perfect tool for removing the batten tape (old driptape).
Photo Pam Dawling

I pulled off the old stuff, using an office staple remover to extract the old staples. I reused the scrap driptape we had been using as batten tape (still years of life left for it in that role!) My approach to agricultural plastics is to buy the most durable and treat them gently to make them last as long as possible. We had two partial rolls of the bubble foil material in the shed, so I used those, but found myself 14 ft (4 m) short, so we had to buy some more. I don’t know about durability, but the Reflectix product was the sturdiest at the start. How long would this stuff normally last? Two changes in 2003-2019 = 16 years. 8 years is too long! 6 or 7 seems like it might be OK. Ask me in 2025!

A quick crop of Tokyo bekana Asian greens for salad, in front of the new bubble foil.
Photo Pam Dawling

Removing the shadecloth

The 15 year-old shadecloth on our hoophouse is still serving us every summer.
Photo Pam Dawling

In the summer we cover our hoophouse with a large sheet of shadecloth. We pack it away in the second week of September. (It helps if the first bed of winter crops (planted September 6-7) has had a chance to germinate before we make it hotter in there by pulling off the shadecloth.) Our shadecloth is 50% knitted polyethylene. I think 45% would be better than 50%, next time we buy. And I think buying 100 ft (30 m) would be better than just the 96 ft (29 m) length of the hoophouse. See the way the shadecloth pulls away from the ends in the photo.

Our hoophouse in 2008 when the shadecloth was in better condition.
Photo Pam Dawling

We are still using the shadecloth we bought in 2004, 15 years later. It has a few mouse holes that happened in storage, and the fabric is starting to lose its strength and rip. We used to fix  snap-on grommets to the center-line of the shadecloth at the ends and tie with ropes onto the end wall structure. But nowadays the shadecloth is too weak to withstand the firm pull we need to give to get those ends in place. So we get a hot spot at each end of the hoophouse. We’ll need to buy new shadecloth in the next couple of years. Probably we can cut the old piece up into 7 ft (2 m) strips to use over beds of lettuce outdoors. It won’t need much tensile strength for that task.

We use snap-on grommets, big hooks in the baseboard and a long piece of rope, to hold the shadecloth along each long side of the hoophouse.
Photo Pam Dawling

Fall hoophouse bed prep and shadecloth removal

Our hoophouse is covered mid-May to early-September with a large shadecloth.
Photo Twin Oaks Community

Today we’re removing the giant piece of shadecloth that has been over the top of our hoophouse since mid-May. We’ll unclip the ropes, roll them up, then pull the shadecloth off onto the ground, roll and bundle it up. It’s important to store it so mice can’t get into the bundle and make holes. We already have a few of those!

The shadecloth is held on by ropes zig-zagging between snap grommets on the shadecloth and large hooks on the baseboard.
Photo Twin Oaks Community

We’ve just finished preparing the first of our 7 hoophouse beds for the winter greens. Crops grow so fast in the hoophouse, and the organic matter in the soil is consumed at a rapid rate. Every new crop requires a fertility boost. In the fall, we prepare our beds by removing all the summer crops, and spreading four or five wheel­barrows of compost per 4′ × 96′ (1.2 × 29 m) bed. This is a generous 46 gals/100 ft2 (or 680 L/36 m2 bed)or more. A full wheelbarrow generally holds six cubic feet (44 gallons or 170 liters). 1 ft3 = 7.5 US gals. An inch of compost is about 8 ft3/100 ft2, or 60 gals/100 ft2; 20 gals/100 ft2 is 15 tons/acre (8.6 L/m2). Other professional growers use any­where from 12–40 gals/100 ft2 (5–17 L/m2). Some use much more.

There are 3 concerns about using too much compost: high phosphorus levels, raised salt levels and nitrate accumulation. Some growers like to do two years of high compost rates (40 gals/100 ft2, 17 L/m2 or more), then reduce the rate to half that and add fish or kelp, at only 5 oz–8 oz/100 ft2 (15–24 gm/m2) per year. Sustainable alternatives to compost in­clude organic pelleted chicken manure, alfalfa meal, etc.

Broadfork from Way Cool Tools.
Photo Way Cool Tools

A few years after we put up our hoophouse,  we noticed that despite our best efforts, we were walking on the edges of the beds and compact­ing them. Initially we simply loosened the edges of the beds with a digging fork. We then noticed that the plants on the edges grew better, and we realized the whole bed width needed loosening. If you have designed your hoophouse to use trac­tor equipment there, that will deal with soil com­paction. We wanted our hoophouse to be free of internal combustion engines and fossil fuels, and the broadfork has provided the solution. Ours is an all-steel broadfork from Way Cool Tools. We do an annual broadforking each fall, before planting our winter greens.

We set nylon twine to mark the bed edges, holding it in place using sod staples. The string alone has not been enough to stop us walking on the bed edges. Loose soil is important because our winter crops grow all the way to the edges of the beds. After spreading compost, we broadfork the beds, then vigorously work the compost into the top of the soil with scuffle hoes and rakes. We learned the hard way the importance of raking the soil to a fine tilth immediately after broadforking — you don’t want to let the broadforked clumps dry out into bricks before you rake! See the photo below and imagine what could happen!

Hoophouse bed broadforked to aerate the soil without inverting.
Photo Pam Dawling

I wrote about our bed prep method and tools, and also our outdoor sowings for transplanting into the hoophouse, with a special focus on suitable lettuce varieties in my post Sowing hoophouse winter crops here in Sept 2017.

We have just started planting our late fall, winter and early spring crops in the hoophouse. We are  pre-sprouting our spinach for a week in a jar in the fridge. Soak the seed overnight, drain it in the morning, fit a mesh lid on the jar, and lay it on its side in the fridge. Once a day, give the jar a quarter turn to tumble the seeds and even out the moisture. If the seeds are a bit wet when you need to sow them, and clumped together, pour them out on a cloth to dry a bit before sowing.

We will sow five crops in our first bed on September 6 and 7– spinach, tatsoi, Bulls Blood beet greens, radishes and scallions. On September 15 we sow lettuces, chard, pak choy, Chinese cabbage, Tokyo Bekana and Yukina Savoy, in an outdoor bed to be transplanted into the hoophouse in a few weeks, after we’ve prepared another bed.

We plant crops closer in the hoophouse than outdoors, and closer to the edges of the beds. We don’t have many weeds in the hoophouse, and the paths are marked off with twine, to keep us from stepping on the beds. We find that the soil does slump and compact some of its own accord, even if we don’t step on the edges (and of course, some feet do find themselves on the bed edges), hence the once-a-year broadforking.

Young spinach plants (and henbit!) in our hoophouse in December. This is our second sowing, not the early September one.
Photo Pam Dawling

Step-by-step guide to hoophouse fall bed prep:

  1. Remove the summer crops to the compost pile,
  2. Spread a generous layer of compost over the whole bed surface.
  3. Gather the soil staples and move the drip tape off to one side or the other,
  4. Broadfork the whole bed, but not all at once. Only broadfork the amount of space you have time to rake immediately, otherwise the warm hoophouse conditions dry out the soil and make it harder to cultivate into a fine tilth, which is the next task. We tackle 1/3 bed each day.
  5. To use a broadfork, go backwards working the width of the bed. Stab the tines into the soil and step on the crossbar, holding the long handles. Step from foot to foot until the crossbar touches the soil, with the tines all the way in, then step off backwards, pulling the handles towards you. This loosens a big area of soil, which hopefully crumbles into chunks. Lift the broadfork and set it back in the soil about 6” (15 cm) back from the first bite. Note: you are not inverting the soil – this is not a “digging over” process. Step on the bar and repeat.
  6. Sometimes we use a rake, breaking the clumps up with the back of the rake, then raking the soil to break up the smaller lumps, and reshape the bed. More often we use a wide stirrup hoe very energetically. This isn’t the job stirrup hoes were designed for (that’s very shallow hoeing), but the sharp hoe blade does a really good job of breaking up clumpy soil.
  7. We’ve found it important to lay the drip tapes back in place in between each day’s work, so that the soil gets irrigated when we run the system and stays damp. We don’t want dead, baked soil.
  8. When the bed is prepared, we measure out the areas for different crops and mark them with flags.
  9. Next we use our row-marker rake (bed prep rake) from Johnny’s Selected Seeds.
  10. After the rowmarking, we deepen the furrows if needed (often it’s not needed), using a pointed hoe, then sow the seeds.

For more on winter hoophouse crops, see

Planning winter hoophouse crops for our step-by-step process for hoophouse crop planning

Cold-tolerant lettuce and the rest, our January 2018 assessment of the varieties we grew that winter and which survived the unusually cold spell we had.