Greenhouse Yield Calculator UK — Annual Harvest Estimate
Waldenhaus · Free tools · 02 — Yield
Estimate your annual harvest.
Pick a NORDIC size and the crops you'd grow — we'll estimate annual harvest in kilograms and supermarket-equivalent value. Based on realistic UK home-growing yields with active venting and reasonable care.
8×6 · 5.2 m²
8×10 · 7.8 m²
8×13 · 10.4 m²
8×16 · 13.0 m²
8×20 · 15.6 m²
Estimated annual harvest
~85 kg
≈ £340 supermarket-equivalent value per year
Crop-by-crop breakdown
Estimates are based on UK averaged growing data with NORDIC's 4 mm twin-wall CrystalLight polycarbonate, screw-fixed glazing, and active venting. Actual results vary by season, exposure, varieties chosen, and care intensity. Supermarket-equivalent uses £4/kg average across mixed crops at typical UK retail.
— How it's calculated
How the yield calculator works
The calculator uses three inputs: greenhouse size, dominant crop, and grower experience. It allocates 70% of the floor area to actual growing space (the remaining 30% covers paths, staging, and seedling stations), then applies crop-specific yield rates per square metre.
Typical UK home-grower yields per square metre with active venting and reasonable care: tomatoes 8–10 kg/m², cucumbers 8–12 kg/m², peppers 3–4 kg/m², leafy greens 2–3 kg/m² (cut-and-come-again), herbs 1–2 kg/m². The experience multiplier — 0.65× for beginner year-one, 1.0× intermediate, 1.4× experienced — reflects the real-world spread between someone learning from scratch and someone with four years of crop rotation, variety selection, and pest management dialled in.
How realistic are these numbers?
They're conservative middle-of-the-road UK figures. A skilled grower with optimised indeterminate tomato varieties on cordon training can hit 15+ kg/m² — Charles Dowding's no-dig approach regularly exceeds these baselines. A first-season beginner working with garden-centre plug plants and minimal feeding usually lands at 50–65% of intermediate yields.
The supermarket-equivalent value uses £4/kg averaged across mixed crops at typical UK retail. Tomatoes alone retail at £5–8/kg in 2026, peppers £6–8/kg, cucumbers £3–4/kg each (about £4/kg by weight). The blended £4/kg is a defensible mid-point. Organic pricing (£6/kg+) and farmers' market prices push this higher; supermarket basic ranges push it lower.
Payback isn't the whole story
The "payback in X years" figure is useful for framing but doesn't capture the full economics. A NORDIC greenhouse is engineered for a 30+ year service life. The frame holds up because the 45×45 mm Swedish pine from sustainably-managed forests cross-section is twice the timber mass of comparable kits, the joints use 1.2 mm galvanised steel (not aluminium that work-hardens and cracks), and the screw-fixed CrystalLight panels don't blow out in storms the way spring W-clip glazing does.
Across 15 years of typical use, a £1,299 NORDIC-L pays back in vegetables roughly 5× over. Across 30 years (the realistic design life with re-treatment every 2–3 years), 10× over. That doesn't count the seasonal extension — your tomato season runs Mar–Oct instead of June–Sept outdoor, doubling the cropping window — nor the variety access (you can grow heritage varieties unavailable in supermarkets) nor the food security against supply shocks.
What the calculator doesn't show
Three things the numbers can't capture:
- Quality: a tomato picked at full ripeness 30 minutes before eating doesn't compare to a supermarket tomato picked green 14 days earlier and gas-ripened. The £4/kg figure understates the experiential value.
- Seasonal extension: outdoor tomato season in the UK runs roughly mid-July to early September. In a NORDIC, you start harvesting late May (with heated propagation) or early-mid June (cold start), and continue through October. Doubles or triples the productive window for the same plants.
- Year-round growing: leafy greens, herbs, overwintered brassicas, and propagation for spring all extend value into months when nothing grows outdoors. The calculator estimates seasonal yields; year-round growing adds 30–50% more value on top.
— Questions, answered
Frequently asked questions
Why are tomato yields lower in the calculator than I've seen elsewhere?
Many online sources quote yields per plant rather than per square metre. A well-managed indeterminate tomato plant produces 5–8 kg over the season, but it takes ~0.8 m² of space (with vertical training). 5 kg per 0.8 m² = ~6 kg/m². Our 8–10 kg/m² figure for tomatoes assumes dense planting with strict staking. Beginner first-year tends toward 4–6 kg/m²; experienced growers reach 12 kg/m²+.
Do these yields assume heating?
No — the baseline assumes a cold greenhouse with passive solar gain through the 4 mm CrystalLight polycarbonate (which transmits ~85% light and insulates ~33% better than single glass). With heated propagation (electric mat from January) you can shift season-start forward 4–6 weeks, increasing total yield by 15–25%. Active heating through winter (paraffin or electric) extends growing further but adds operating cost.
How do these compare to allotment / outdoor yields?
Per square metre, a well-managed greenhouse produces 2–3× more than the equivalent outdoor space for heat-loving crops (tomatoes, peppers, cucumbers). For cool-season crops (leafy greens, brassicas, peas), the advantage is smaller — maybe 1.3× — but the season is twice as long. The £4/kg supermarket-equivalent value applies equally; a greenhouse just compresses more harvest into less space.
What's the real ongoing cost?
NORDIC kit cost (£999–£1,549) is the main investment. Ongoing: re-treatment every 2–3 years (~£40 of wood preservative, 2 hours of labour), occasional polycarbonate cleaning (£0), and modest electricity for propagation mats (~£15/season). No annual replacement parts. See our full cost breakdown for the 10-year total.
Does the yield change if I grow organically?
Yields are roughly comparable to conventional home growing — UK home gardens are typically lower-input than commercial farms regardless of "organic" label. The supermarket-equivalent value goes UP if you compare to organic retail prices (£5–8/kg). So organic home-growing has higher financial value, just not higher yields.
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