If you’re like me, your houseplants gradualy die of neglect. After bringing home a cactus or a fern, you put it in good spot (a bright one) and it’s happy…for days. Then it yellows; then its leaves drop off.
Common causes: Overwatering, ignoring humidity. Often it’s really the light that’s at fault. Specifically, the wrong amount of light plus the wrong duration, all combined.
Stop Guessing How Much Light Your Plants Need
Light is generaly considered one variable, with most people seeking out a dark corner or a sunny spot. In reality, there is two: intensity (the amount of light hitting the leaf) and duration (how many hours a day the light is on).
Eight hours of very dim light is not more better than two hours of super-bright light, even though many people try to fix weak light by leaving lamp on all night. Not only doesn’t it feed the leaves, but this will also confuse the plant’s internal clock.
Intensity bands help you know how to position your plants properly. Some fern thrive in deep shade (about one hundred foot-candles). Place one of those under a five-thousand-foot-candle grow light that’s super-bright, such as an LED, and its foliage will burn (bleach) right off. That’s just too intense for its delicat leaf structure.
Succulent plants and cacti wants full sun, often well over seven thousand foot-candles. If you put a cactus on your north-facing windowsill, it will stretch and get spindly, looking weak and thin. Hours of day don’t count when each one’s so feeble it doesn’t trigger effective photosynthesis.
And how long? That’s important too, particularly with flowering plants. For example, chrysanthemums and other such short-day plant require long days (and long nights) to tell them it’s time to flower. If grown under 14 hours of artificial light each day, they will grow nice and bushy but not flower. What are they waiting for? Long nights, that’s the trigger.
Conversely, certain plants (tomatoes, for instance, or peppers, which we think of as fruiting plant), are long-day plants that require long days to enable them to pay energy price of fruit set. Why do greenhouse growers leaves lights burning all winter long? They do this to extend the day and keep the plant in production mode.
So what? The bottom line is that guesswork stops here. Unless you have an even-light space indoors (good luck), don’t guess. You may think the room’s corner looks bright to your eye, but that light meter may be reading only two hundred foot-candles on the floor. Your plants are positioned above that; the light will be different up there.
Here is the simple part. Buy an inexpensive light meter app/device. Measure the foot-candles where the canopy is, meaning up off the ground. Then program your timer accordingly. Use long days and high intensity if the plant is a fruiting crop. Use shorter days and lower intensity if it’s a shade lover.
Plants aren’t pets; they’re machines, and exacting ones at that, with particular inputs required from us. No amount of good intention will matter to them. What matters is what’s on their chlorophyll: the photons. When we match the input (intensity) to the output (duration), we cease to fight the plant’s biology. We no longer wonder why the flower never shows up, or the leaves is so thin.
The light isn’t mysterious. It’s math. And when you do the math, it grows. Your next orchid may thrive where your first fern died on the very same window sill, as long as you could of checked the math before the decor.