Here’s a trick question: What’s the single most important factor when growing indoors? The answer is, of course, that there’s no single factor that determines success. Plant lighting, temperature, water, potting conditions and nutrients all play an inter-related role. All are crucial. You can’t separate one from the other. You may have perfect light in religiously timed and measured lumens. But if your plants don’t have enough moisture, or they’re exposed to extreme temperature variations, well, all that money you spent on lights is wasted. Likewise, if you put plants out on your sun porch — plenty of light! — but the dead-of-winter sun shines in only six hours each day, your plants will do little but maintain (if that). Worse, if that six hours of sunlight heats the room beyond what the plant can bear — or if it loses a lot of heat through all that glass at night — your plants will be lucky to survive the variations let alone flourish.
Forget the trick questions. Instead, we offer this absolute statement: The most wide-spread misconception concerning indoor plant lighting is that your plants will do fine in a sunny windowsill. “Growing” is the key word here. You may be able to overwinter houseplants or a potted herb or two in a sunny window. But for growth? You need to recreate the complete, concentrated, and long light conditions that plants experience outdoors during the summer. (more…)