Windowsill strawberries are most tempting in winter, when store berries are pricey and taste like nothing. Winter is also when the plants get the least light. Before you buy a system, two numbers are worth knowing: how many berries one hydroponic plant yields in good conditions, and how much light it needs to get there.
The first number comes from Illinois Extension, which weighed the 2023 harvest of three day-neutral strawberry varieties grown hydroponically. The second comes from Ohio State University’s recommendations and NASA climate data for Kyiv, Ukraine, which sits at about the latitude of Winnipeg.
How much one plant yielded in the Illinois trial
The plants grew in an unheated high tunnel in southern Illinois, in vertical stacks filled with perlite. There was no supplemental light. A drip fertigation system fed them at an EC of about 1.8 mS/cm. Berries were picked 100 times between May 5 and October 18. Marketable yield per plant:
- Monterey: 0.76 lb (345 g), the top yield and the best flavor;
- San Andreas: 0.54 lb (245 g), the largest berries;
- Albion: 0.48 lb (218 g), the smallest and somewhat sour berries.
In berries, that is not a lot. The average Albion berry in this trial weighed about 0.4 oz (11 g), so one plant gave roughly 20 berries over half a year. San Andreas gave about 15 large berries per plant.
The author says plainly that conditions were far from ideal: one shared nutrient solution for every crop in the tunnel, and the hottest months of the year. Fruit quality improved as fall cooled things down, and the plants were still bearing when record keeping stopped. But these plants had plenty of light: southern Illinois from May through October. So 0.5 to 0.75 lb per plant per season is a ceiling for a windowsill, not a floor. Our hydroponic strawberry guide gives the same range.
How much light strawberries need
Plant light is counted in moles of photons per square meter per day, the daily light integral, or DLI. Our PPFD and DLI guide explains what it is and how to measure it.
For strawberries, Ohio State gives these limits: a minimum of 10 to 12 mol per square meter per day, an optimum of 20 to 25, and stress above 30. By their account, the yield of fruiting crops usually rises in a straight line with the total light received over the season. Less light, fewer berries.
How much light a window gets in Kyiv
NASA keeps a sunlight climatology for any point on the planet. We converted the Kyiv numbers to DLI. This is light in the open, under the whole sky:
- December: 4.1 mol/m² per day;
- November and January: 6.0;
- February: 12.0, October: 14.3;
- March: 21.5, September: 26.0;
- April through August: 31.6 to 45.6.
That is still not a windowsill. Glass takes some of the light, the frame and wall cast shade, and a window sees only a slice of sky and gets direct sun a few hours a day. Ohio State estimates that even greenhouse glazing and framing cut 30 to 50% of the light. A windowsill loses at least as much, and exactly how much depends on which way the window faces.
From November through January, even open sky over Kyiv gives 4 to 6 mol, while strawberries need at least 10 to 12. In February and October the open-air figure sits right at the minimum, and a windowsill gets less. From April through August there is light to spare outdoors, and an unshaded south window has a chance of reaching at least the minimum. Only a measurement will tell you whether yours does. So in winter, a windowsill strawberry grows under a lamp, and the window adds only a little.
What grow light you need in winter
If you assume the lamp provides all the light in December, reaching the 12 mol minimum on a 16-hour day takes about 210 µmol/m²/s at leaf level. Reaching the 20 mol optimum takes about 350. For comparison, greenhouses that supplement strawberries usually run 100 to 200 µmol/m²/s, but there the sun supplies the rest.
You can run your own lamp and schedule through our DLI and PPFD calculator. Light should hit the whole leaf canopy of a strawberry plant, so hang the fixture above the plant, not off to the side. Our grow light efficiency guide covers how to pick a fixture.
Variety, system, and pollination
Only day-neutral varieties belong on a windowsill. Short-day varieties usually will not flower under the long day of a grow light. All three Illinois varieties are day-neutral, and their numbers help you choose: Monterey gave the most and tasted best, Albion gave the least. The strawberry guide explains the variety groups and what to do with frigo plants.
For strawberries, pick a system with a substrate and drip irrigation, as in Illinois. We covered why, and how it compares with DWC or Kratky, in our hydroponic system comparison.
And nobody pollinates flowers in an apartment. Without a brush, berries come out misshapen or do not set at all. The strawberry guide covers hand pollination too.
Windowsill strawberries: the takeaways
- In good conditions, a day-neutral hydroponic plant gave 0.48 to 0.76 lb (218 to 345 g) of berries from May through October (Illinois Extension, 2023). Treat that as the windowsill ceiling.
- Strawberries need at least 10 to 12 mol of light per m² per day, ideally 20 to 25 (Ohio State University).
- In Kyiv, from November through January, even open sky gives 4 to 6 mol, and a windowsill gets less.
- In winter you need a lamp at about 210 µmol/m²/s for 16 hours to reach the minimum, and about 350 for the optimum.
- Day-neutral varieties only, and pollinate by hand.
