How do I grow a basil plant tall?

Question

In my workplace we have a competition on who can grow their basil plant the tallest in 9 weeks. I know next to nothing about gardening, so I would appreciate tips. The plants are store bought, so already "grown up" (mine is 14 cm).

Here are my questions and musings so far:

• The pot it came in is quite small. Could I benefit from replanting it in a larger pot?
• Should I put a lamp over it and cover the sides in something dark, forcing it upwards?
• Do I need a special lamp or is any lamp ok, including LED?
• I suppose I should tie it up to a stick to help it stabilize?
• Should I use fertilizer or some nutrition other than just water?
• Could I benefit from hanging it upside-down, with a lamp underneath, to make gravity stretch it?
• I read about someone growing marijuana saying that you can make a plant grow larger by pruning the lower leaves. Is this true?
• Can I stretch the plant somehow? Perhaps if I combine hanging it upside down and tying a small weight to it? (I like this idea :)

And also the basics:

• How much should I water it? (I think basil should be watered from below)
• How much sun and warmth does it need?
• If I use a lamp, should I turn it off X hours each day?
• How strong should the lamp be?

Answer 1

If all you want is a tall plant, and it doesn't matter whether its bushy, well grown and attractive, put it in low light levels - it'll suffer what's known as etiolation, meaning the stems gets longer and weaker and paler, and the spaces between the leaves are greater up the stem. It won't look at all well, but it will be taller.

Other methods - turn it out of its pot, gently - if there are roots coiling round or you can see roots hanging at the bottom, by all means put it in a larger pot, but only a pot the next size up, not an enormous one. Use good potting compost, and water well. Watering after that should be when the surface of the compost feels a little dry to the touch, at which point, give it a good water, but don't allow it to stand in any water collected in a tray or outer pot after 30 minutes (empty it out). You can add a higher nitrogen feed to it when you water (once a week, twice a week at a push, diluted correctly). In the UK, that would be something like Baby Bio houseplant food, or Phostrogen, but look for the NPK readout on the carton or bottle - the N should be the highest number for what you want.

Removing lower leaves as it grows might very well help it to become taller, but so will good light levels from above - as you suggested, a grow light placed above at the optimum distance will encourage growth towards that light. You can check which light you need and the distance by Googling - hash growers are experts at this, and there's lots of info on the web. The distance between plant and grow light varies according to the plant, but its usually around 10 inches between the top leaves and the light. It would mean some financial investment in a proper grow light - I think there's one on the market that comes on a frame so you don't have to set up your own supports from the ceiling or on struts, but how useful it is, I don't know. Basil is a mediterranean plant, and likes warm conditions, so don't keep it somewhere it gets below 60 deg. F at night. As for whether it needs some hours of darkness, to be honest, I've no idea whether this particular plant does or doesn't, but I would not have it lit for 24 hours, I'd give it an 8 hour rest overnight.

As for the idea of 'stretching' the plant with a weight, well, I haven't laughed so much in ages, thanks for that, but no, it ain't gonna work, so ditch that idea.

Answer 2

another thing you can do, is keep denuding the stem of leaves. If the plant has only 1 baby set of leaves on top of the stem, it will put all it's energy into pushing another set out. I wouldn't combine this method with etoliation, because the plant at that point probably won't get enough light to feed itself let alone grow.

If you get ANY flower spikes, cut below the first set of true leaves underneath the spike or you'll just grow another spike (which will only grow a few more inches or cm.

Basil that you denude from the bottom up gets tall woody and leggy very quickly, which is why when growing basil for kitchen use, you usually harvest by cutting above the bottom set of healthy leaves, this pushes two new stems up and allows the plant to get bushy instead of tall and leggy. You want to do the opposite which is supporting a single stem that grows quickly, so keep the stem denuded and only leave 2 opposing set of leaves at the top so it will keep pushing higher.