Thai basil is a must have ingredient for many Thai/Vietnamese dishes and therefore it’s a must have in my kitchen! Thai basil tastes different from the more common Italian basil used in North America, a bit more peppery and some say with notes of licorice or anise. I’m not sure how to describe the taste, but I knew I needed a consistent supply of Thai basil to make my favourite Thai dishes during the restrictions of 2020 (and 2021) and so I set out to see if I could successfully grow Thai basil indoors.
Prior to those restrictions, I sourced my supply of Thai basil from a large Asian grocery store near my home (Toronto is a wonderful city for foodies!) But once we switched to shopping for groceries once a week, at one store, that was a problem. I also didn’t love that when I bought herbs from that store I could only buy a large bundle (meaning half of it ended up in the compost) and that it came packaged on a Styrofoam tray and wrapped in layers of cellophane, creating lots of unnecessary garbage!
Now that I’ve figured out how to grow Thai basil indoors (and outdoors in the summer), I can’t see going back to using store bought. It is so much more convenient, economical, and environmentally friendly (no garbage!) to grow my own.
Growing Thai Basil Indoors
The first thing one needs is some Thai basil plants. I found that three plants were enough for our needs most of the time; that gave me enough leaves to make my favourite Thai recipe at least once every two weeks.
If you are able to buy small That basil plants that could be an easy way to get started. However, they’re difficult to find most of the time, so I grow mine from seed. A package of seeds will cost about the same oreven less than one plant, and will supply all of your needs, and more, for a few years. It’s easiest to find the seeds in late winter and on into spring at garden centres or big box stores, but other online sources can be found through Google if you can’t find any locally.
I’ve come across debates about which is the “true” Thai basil and what variety of seed is authentic. I’m not going to get into that debate because I just don’t know enough about it. I do know that I’ve purchased a couple different brands of seed labelled “Thai basil” and the resulting plant leaves taste like what I buy at the grocery store and what is served at good local Thai restaurants.
Growing Thai Basil From Seed
I usually start my seeds in a 4” pot or small plastic produce tray with holes poked in the bottom. I fill the pot or tray with damp potting soil, sprinkle a few seeds on top (e.g. if I want to grow 4 plants, I will plant no more than 8 seeds), cover with some more potting soil about ¼” deep, press it down lightly so that the seeds and soil are all making contact, and then water it. I then put it somewhere warm, check on it once or twice a day to ensure that the soil stays damp (not wringing wet and never dry), and wait for little sprouts to appear. Sometimes I pop a clear plastic bag over top of the pot to help keep humidity up while the seeds are germinating.
As soon as sprouts appear I make sure the plants are close to a bright light source (more on that in a minute) and I grow them on until they start to look like viable plants. If more plants germinate than I need, this is the point where I need to (ruthlessly) thin out the weakest ones, only leaving the number of plants I want.
Once the plants are large enough (3” tall or so) I carefully repot each of them into their own 4” pot. I use regular potting soil (not garden soil or topsoil. Read why here). I don’t put stones or anything else in the bottom of the pot. My ingredients are just a pot, potting soil and the plant.
Growing Thai Basil Plants
Small plants can grow quite well in 4” pots for several months. If I find that they need to be watered every day then that’s my signal that they need to be moved on to a bigger pot. Note that it’s better to move up pot sizes gradually, rather than put a tiny plant in a large pot—it will not thrive.
Every time I water my Thai basil plants I do so thoroughly. Water until water runs out of the drainage holes at the bottom of the pot (Note: if your pot doesn’t have drainage holes it’s not a pot, it’s a pot cover. Find yourself a pot.). Do not water again until the top 1” or so of soil has dried out. I don’t usually stick my finger in the soil every time—instead I usually lift the pot to feel how heavy it is. If it’s very light the plant needs to be watered. Thai basil is also very good at communicating when it needs water—the leaves wilt really fast. Thankfully, they rehydrate well if you respond with a thorough soaking within a day.
There are not enough hours of sunlight in North America to grow Thai basil well on a window sill. You need to use artificial light, and that night needs to be close to the plant and on for about 16 hours a day.
The good news is that you do NOT need fancy, expensive grow lights. You don’t need full spectrum, high intensity, red light, blue light, yadda, yadda, yadda. Those grow light setups are only really necessary for growing cannabis. All you need to grow basil year round (or start your tomato seedlings or most other things) is a standard, cheap shop light. I used to use regular fluorescent tubes on my plant stand and they worked just fine, but now I have LED shop lights similar to this one*.
The key is to keep the light close to the plants (mine are no more than 12” away from the light) and to have the light on for about 16 hours a day. I have mine set up on a timer.
The potting soil that I usually use has some grains of slow release fertilizer integrated into it. If yours doesn’t, you might want to incorporate some slow release feed (like this one*, or find an organic option if you prefer) into your potting mix when you pot, or repot, your plants.
At some point the plant will eat through all of the nutrients in the soil. It will tell you that it’s hungry through yellowing leaves and less vigorous growth. Once I see this signal, I start to add a small amount of liquid fertilizer to the water about once a week.
Once plants are well established it’s time to put them to use! I use scissors to snip off some stems just above a growing node. On the picture below, I’ve picked this entire large stem, but if this was a small Thai basil plant, the blue lines show where I would make my cuts.
Cutting off the ends of stems likes this helps to keep the plant small and bushy, as new growth will spring up wherever a cut has been made.
You can see that I’m only getting a few sprigs off of each plant. This is why I like to have several plants to harvest from at any one time.
Once I pick leaves for dinner I give the plant some time to reinvigorate itself before picking again. Depending on how hard you cut it back each time, this could be anywhere from a few days to a few weeks. But if you take good care of your Thai basil plants there is no reason that you can’t keep the same ones going from fall to spring, with many delicious meals along the way!
Flower buds will form at the end of stems if you don’t cut them back. I usually pinch them out, as I don’t eat them and they’re taking energy from the plant. But sometimes I let them be, as they’re kind of pretty and that’s a good thing too.
I know this picture is a little hard to look at, as I have a reflective mylar blanket* draped over my light stand to direct more light at the plants, but I’ve used blue arrows to point out the Thai basil flowers.
Can I grow other types of basil indoors like this?
You can, but most Italian basil plants have a much larger growth habit than Thai basil (which tends to be a relatively short plant, even when grown outside in the garden) and space can quickly become a problem when you’re growing plants under lights. If you have a large space and a few shop lights then yes, the same principles apply.
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