# Hoop houses and other cover **2026-10-08.** A companion to [plant-conditions.md](plant-conditions.md). A hoop house — a high tunnel — is **a second site inside the farm**, with its own climate. It is also the place where fieldmesh's sensors pay off fastest, because a closed tunnel on a sunny day can cook a crop in an afternoon, and an open one on a clear night can freeze it. [structures-list.csv](../data/structures-list.csv) lists ten kinds of cover, from floating row cover to heated greenhouses, and the livestock versions: hoop barns and mobile poultry houses. ## What a high tunnel changes | dimension | effect | how sure | | --- | --- | --- | | season | adds roughly **two to four weeks** at each end | the figure extension services give | | winter nights | warmer, by an amount that varies by tunnel, cover and night; a row cover inside adds about another 1.5 degrees on average, more on the coldest nights | **measure it** — see below | | rain | none: **everything must be irrigated** | physics | | wind | cut | physics | | light | most, not all, gets through the film; diffused | by film | | heat by day | trapped — overheating within hours if the sides stay shut | the main risk | | soil salts | build up, because no rain leaches them | measurable: the soil survey's EC, a soil test, or an EC-reading probe | | pests and disease | fewer rain-splashed leaf diseases; more mites, aphids and powdery mildew | | | pollination | bees are shut out; crops that need them need a hive inside (bumble bees are the usual greenhouse pollinator) or hand pollination | | **Cost-share.** NRCS pays for high tunnels through EQIP, as conservation practice 325, "High Tunnel System", offered in every state; payment caps are set by each state. ## What the matcher says `plant_match.py --cover high-tunnel` matches a site as a crop under a tunnel sees it, changed only as far as is defensible: the season lengthened by two weeks at each end, rainfall dropped (irrigated), and the winter low left as it is outside unless a measured gain is given (`--winter-gain-f`). Only what is grown under cover is judged — the first run happily put bur oak in a hoop house. At McAllister Farm, of the 253 plants that are grown under cover, **193 have no USDA PLANTS characteristics** — tomato, lettuce, spinach, peppers, potato, beans, peas, ranunculus, anemone, lisianthus among them. Only a handful change verdict (eggplant, claytonia, blueberry, rosemary). The machinery is right; the crops tunnels exist for are exactly the ones PLANTS does not cover. Since then the DSSAT crop models cover tomato, pepper, cabbage and the beans in the open ([site-match-tennessee.md](site-match-tennessee.md)); running them under a tunnel's measured climate is the natural next step once a tunnel is instrumented. ## Measure the tunnel instead The figures above are general. What a grower needs is *their* tunnel's, and fieldmesh already has everything needed to measure it: an air temperature and humidity sensor inside, one outside, a soil probe inside. | question | measured as | | --- | --- | | how much warmer on winter nights | the inside-minus-outside nightly minimum, by month and by outside minimum — it shrinks on clear, still nights | | how much longer a season | inside frost dates against outside, from the same pair | | how often it overheats | hours above a crop's limit, and how fast it climbs after sunrise with the sides shut | | whether salt is building | soil EC over the seasons, against outside | | disease pressure | hours of high humidity and condensation | The first three are what `--winter-gain-f` and the season extension should come from once a tunnel is instrumented, and `modules/advise/tunnel_gain.py` computes them from two `time,value` series (inside air, outside air): python3 modules/advise/tunnel_gain.py inside.csv outside.csv --limit-c 35 It bins each night's gain by how cold the outside night was, hands `plant_match.py` the 10th percentile of the gain on the coldest nights (below −5 °C, or below 0 °C if a winter had none) — so the figure errs cold, which is the safe side for a frost verdict — and reports the inside and outside frost-free seasons and the hours above the crop's limit. **Tested against the virtual farm, not yet against a tunnel.** sim/physics.py now has a `Tunnel`: inside air relaxing toward the outside plus trapped sun by day and the soil's stored heat by night, a night gain that falls from 3 °C on a mild night to 1 °C on a clear night at −5 °C, and sides that go up at 27 °C. A simulated year, sampled hourly the way a logger would, gives back: | outside night | nights | inside warmer by (median) | | --- | ---: | ---: | | below −5 °C | 111 | +1.1 °C | | −5 to 0 °C | 54 | +1.7 °C | | 0 to 5 °C | 50 | +2.7 °C | | above 5 °C | 151 | +3.1 °C | — the gain the physics was given, recovered without being told it, with `--winter-gain-f 2.0` for the matcher and a frost-free season 23 days longer inside. The same tunnel with the sides never opened spends 507 hours above 35 °C; vented, none. These numbers are the model's, not a tunnel's: what the test proves is that the tool reads a gain correctly, and what it cannot prove is what a real tunnel's gain is. The first instrumented tunnel replaces the table. (The Harrow Bend scenario's own hoop-house sensor read a flat outside + 6 °C until 2026-10-09; it now reads this model, and the simulator's tests all pass with it.) **Alarms first, automation later.** Overheating and freezing are the fastest failures on a farm, so a tunnel is the strongest case for layer 1's alerting. Opening and closing roll-up sides by motor is a *command*, and v0.1 defers commands until a season of evidence on the observation path — deliberately, because commands carry the liability. A tunnel is likely the first place a farmer will ask for them. ## Siting a tunnel The site profile already carries what siting needs: slope and drainage from the soil survey (a tunnel on a wet or steep spot is a tunnel full of water or sliding), day length and solar radiation by month (winter light decides what will grow in January), and the wind and snow a frame has to bear — the last two not yet in the profile. ## Animals under cover Hoop barns — the same frame with a fabric roof and deep bedding — house finishing hogs, cattle on winter feed, sheep and goats at a fraction of a barn's cost, and the bedding becomes compost: the fertilizer list's manure, already composting. Mobile poultry houses follow cattle across pasture, which is one of the combinations on the interactions list. Both have the tunnel's main risk, heat; the site profile's heat-stress estimate applies.