The accompanying picture is a flat of Genovese Basil, grown indoors, early this season...before it warmed up outside. There are a couple of purple basil seedlings in there, too, that I just threw in for fun.
The rest of this post is going to tell you exactly what you need to do to grow basil indoors all winder long. I have given you way more information than just the basics so if you have any problems you might be able to find the answer here. The process is actually pretty simple.
Instead of planting one or two basil plants, I plant an entire flat, densely seeded and meant to be cut all at once for pesto, preservation, etc. It takes 4-5 weeks and can be done in succession, for a continuing harvest. The basil grown in the picture was grown under a regular fluorescent light fixture, on my back porch. I used a couple of bricks at each end to raise the fixture as the basil grew but that was just what I had available to use. I have also used varying sizes of glass jars...anything to balance the light on to raise the level of light as the plants get taller.
I use the black trays that go under flats of plants (like from a nursery) to plant my seeds. I use new, clean ones and sterilize them with hot water and vinegar. Because I grow food plants for a living, I have access to lots of products that most people don't have handily around the house, so no worries of you don't have one or more of those trays. You can use about any type of planting container, from a dishpan to a clay pot. You just need to make sure that there is good drainage because seedlings will "damp off" if the growing medium stays too moist.
I use a quality organic growing medium that is formulated especially for starting seeds. You can get something similar at most garden centers. I use this type of medium because it gives optimum results.
Do not use any planting medium that has large pieces of bark or uses watering crystals.
Spread your planting medium evenly in the flat. Soak it well, until it is wet all the way to the bottom of your dirt. Some planting mediums have a lot of peat in them and it is hard to get them soaked thoroughly so be patient. I have actually put my planting medium in a bucket with water before putting in the flats. Messy but effective. And,if you do not let the flats dry out completely between watering, once it has soaked up enough of that initial watering to be wet, the soil will readily soak up water from that point forward.
NOTE: Compost is not really necessary for starting seedlings. Some seedlings can actually be harmed in some cases by a soil that is too "rich" or that holds too much moisture. Yes, seeds will sprout in the compost pile sometimes but that is a different scenario entirely. You want to start indoor seeds in a sterile medium to prevent fungal disease and "damping off". Damping off is literally the seedling rotting away at the soil line which obviously kills it. Since growing indoors does not allow for much air flow, this can be a problem. A small fan, blowing gently on the tiny plants works wonders. Of course, you don't need to get nearly that involved if you just pay attention to your plants.
My best system for watering these filled flats is to do it from the bottom, by placing the tray inside another tray what has no drainage holes and filling the lower tray with slightly warm water. I have also placed them in the sink to do this but then I had a big old time farm kitchen sink that the flats fit into nicely. If you are using a smaller container, that could well fit in your sink and it is much easier to do it that way. Obviously, this can be messy but if you are patient and prepared it won't be. The soil just needs to be moist, not soaked, so whatever method you can use to achieve this should be the one you use. DO NOT OVER WATER SEEDLINGS.
Basil seeds are tiny, so you want to spread them evenly across the flat. I would recommend using about
2 tablespoons of seeds. If you buy seeds in the usual quantities available at most local seed sellers, that is probably the entire package. Just make sure they are not clumped up in one spot and are spread evenly. Use the flat of your hand to smooth them. Pat them firmly but gently into the soil. no need to cover at this point.
Take either Saran wrap or some sort of plastic bag and cover the moist, planted flat. Black or dark is fine, doesn't have to be clear because you are going for warmth, not light at this juncture. Place in a warm (not hot) place for 2-3 days or until you see the tiny seedlings start to emerge. As soon as you see at least 50% of your seeds germinating, take off the cover and put under the lights or in a sunny (not direct) window. While flat is covered, check periodically to make sure there is no mold forming...that means your spot is too warm. If that happens, just take the plastic off and let it dry out a bit. You should not need to water during this time if you did it right.
Once your seedlings are up and growing and you have placed them under their light source, you will need to gently water them on a daily basis. You do not want them to dry out but you also do not want their feet to be soggy (remember about damping off). One of the best suggestions I can make about watering them is to use my method. I take a small plastic bottle (a 16 oz soda bottle is perfect and a good way to recycle it) and use a sharp knife or scissors to make a cross hatched cut in the plastic lid. These slits in the cap will allow you to use pressure to squeeze the bottle and create a gentle stream. You can also use the shape of the bottle to your advantage because you can water near the soil line, instead of dousing the tender seedlings and toppling them over. I suggest practicing your technique before you actually water because too much pressure on the bottle can wreak havoc.
As the seedlings get taller, raise the light to accommodate their height. Fluorescent lights are very cool, temperature wise and you can let the seedlings get tall enough to almost touch the bulb before they are harmed. You should not have to raise the light more than 2-3 times during the entire growing process.
If you do not have a light to use, you can obviously do this in a sunny window. The only problem with that is that you will have to turn the flat once or twice a day because the seedlings will "go toward the light". In other words, they will follow the sun and they will not be straight. That doesn't really hurt anything but if the light is not strong enough they will become leggy and fall over on each other.
I also take several of the healthiest seedlings out at about 3 weeks and plant them in a pot for the kitchen window to just pinch off a leaf or two to add to dishes as I am cooking.
The cool thing about basil is that from the moment the seedling emerges, it tastes and smells like basil. No growing into that....they are born BASIL!!! Once they are about 4 weeks old, they should be ready to harvest as baby leaf. Great in salads, a mini batch of pesto, a garnish, whatever.
At 5-6 weeks, they should be cut and used. I just take the scissors and cut them off about 2 inches above the soil line, pull up the stems and screen the dirt. To reuse the dirt, you can sterilize it by putting in a pan in the oven, heat to about 250 degrees for 30 minutes and start all over again. The reason to sterilize is to remove any pathogens or fungus that might have contaminated the dirt unknowingly. Better safe than sorry.
And that my friends, is how you have basil all winter long!!!
