Houseplant Light Calculator

It depends on your latitude, and across Canada the spread is much wider than most people expect. On December 21, Abbotsford gets 8h13 of daylight, against 16h13 at the June solstice — a swing of about 8 hours across the year. The far south of Ontario gets just over nine hours in late December while northern British Columbia gets barely six. That difference is why generic houseplant advice written for California does not transfer here.

It depends on the plant, not the room. Low-light plants — snake plant, ZZ, pothos, cast iron plant — generally coast through a Canadian winter on daylight alone if they are near a window. Bright-light plants are the ones that genuinely suffer: fiddle-leaf figs, succulents, citrus and most culinary herbs want something closer to twelve hours, which no Canadian city provides between roughly November and February. If you are going to run one light, run it for those.

No, and this is the most important limitation of any calculator like this one. Day length is exact — it is solar geometry, computed from your latitude and the date. What reaches the leaf is not: it depends on which way the window faces, how close the plant sits to the glass, whether the glazing is coated, and what is outside casting shade. Latitude sets the ceiling on how many hours are even available; it cannot tell you the intensity at the plant. Use the hours here as the budget you have to work with, then judge intensity by the plant.

Top up to the plant's target rather than running the light around the clock. If your city is giving nine hours and a bright-light plant wants twelve, three hours of supplement is the gap — and it is usually easiest to add it in the evening on a timer. Almost all houseplants want a genuine dark period, so continuous light is counterproductive as well as wasteful; anything beyond about sixteen hours total is rarely useful for foliage plants.

Follow the curve rather than the calendar. In Abbotsford daylight falls below ten hours and climbs back above it on a predictable schedule you can read off the month table on this page — start when it drops below your plant's target and stop when it rises back through it. For most of Canada that means switching on somewhere around late October and off around mid-February, which is also roughly when houseplants resume active growth and want more water and feeding again.

South-facing, by a wide margin, and more so the further north you are — at Canadian latitudes the winter sun stays low, so a south window takes a long, slanting beam deep into the room exactly when the days are shortest. East gives gentle morning light that suits calatheas and ferns; west gives harsher afternoon light that suits succulents and citrus; north gives the least and in a Canadian winter is genuinely dim, which is where the low-light list earns its keep. Whatever the aspect, closer to the glass is dramatically brighter than a metre back.

They are computed, not looked up — day length follows from latitude and the day of the year by well-established solar geometry, using the CBM model published by Forsythe and colleagues in Ecological Modelling in 1995. The figures were validated against published sunrise and sunset times before this tool shipped: Toronto at 8h55 and Vancouver at 8h11 on December 21, and Toronto at 15h27 on June 21. City coordinates come from the Environment and Climate Change Canada station that serves each city where one shares its name, and from published place coordinates otherwise.

It changes the light, but not the hours. Day length is the window of time the sun is above the horizon, and that is fixed by geometry no matter the weather. A grey week in Vancouver and a clear week in Calgary can share an identical day length and deliver very different amounts of usable light. Treat the hours here as the maximum available, and remember that a persistently overcast winter is an argument for supplementing even where the day length looks adequate.