Growing Greens Indoors

Indoor greens: I think I’ve finally figured out to do it (at my house, anyway)

I’ve puttered around trying to grow things indoors over the winter for years, but I’ve only managed “worth-it” harvests in the last 12 months or so. This could get long…but here’s what I can now harvest about once a week or ten days:

TL; DR – What do you recommend?

I suggest you get two, 2′ wide three-bulb light setups, each with an 8.5 gallon underbed tote underneath. Fill the tote about 6″ deep with the best potting soil you can afford. Sow thickly with a mix of brassica greens (kale, mustard, red cabbage, tatsoi). After about a month, you can harvest by the handful with scissors, leaving the stalks to regrow. They’ll be ready to harvest again in about 10 days. If you plan it right, you can harvest each tub every ten days for a continuous harvest. Each time you harvest, fertilize with your choice of fertilizer.

The long version: What worked

I finally figured out that all of these things are absolutely necessary to grow meaningful food indoors.

  • Growing the right things
  • Lots of light
  • Deep soil
  • Fertilizer

What to grow indoors

For me, it’s all greens. Microgreens (grown just until they have their seed leaves), baby greens (a few true leaves), full-sized lettuce, and some almost full-sized chard and kale. I’ve given up growing anything that fruits or sets a large root (like carrots) – they just need more light and space than I can give them. Those things also would produce a fraction of the food per square foot compared to greens. For my mini-greens setup, it takes them about a month to come to size – then I can harvest about half a pound a week per 2’x1.5′ box. Cut-and-come-again, they just keep cranking out leaves until the soil fertility runs out. Good varieties:

  • Kale
  • Tatsoi
  • Mustard greens
  • Lettuce
  • Red cabbage
  • Collards
  • Chard and beets (takes longer)
  • Spinach (takes much longer)
  • Cilantro

You can go nuts over at Johnny’s Seeds microgreens area (definitely try the Mild Micro Mix), or you can just dump all your old seeds into a jar and spread the seeds thickly. Also check your local feed store for seeds sold by the ounce. You can usually get most of the things on the list above for a dollar or two per ounce. Just don’t buy by the standard garden packet or you’ll go broke.

How much seed do you need? Hmm…maybe a tablespoon of seed per square foot? I confess, I have a hard time restraining myself on these seeds so I don’t really measure. I also use more seed for microgreens and less if I’m letting the plants get a little bigger. But I can say I’ve bought maybe 8 ounces of seed over the last couple years and I haven’t run out yet.

Lots of light

I have a sunroom with a wall of windows on the south side of my house that is designed to capture sun in the winter and shade from the sun in the summer. I’d been assuming that once the leaves fell, this would get enough light to grow things. This year I realized that’s not really true, especially when it’s cloudy. And it’s Michigan, so it’s cloudy a lot in the winter. I’ve tried both T5 fluorescent setups and a couple kinds of LEDs. What seems to matter the most is not the kind of bulb, but the number of bulbs and the kind of fixture they are in.

This two-tier cart setup (plus a similar one-tier version; 24″ wide and 2 bulbs per fixture) from Gardener’s Supply has been my workhorse for years now. I bought it to start seedlings, but now I use it year-round for microgreens, mini greens, and full-sized lettuce. In addition to great bulbs and reflectors, it has a wicking mat setup that the THE BEST for keeping things watered perfectly from beneath. It’s the only “self-watering” setup I’ve ever owned that has actually worked. I pour about a gallon of water into the tray once a week, and everything stays really, really happy.

This Agrobrite T5 (24″, 4 bulbs) with great built-in reflection is probably the best light I own. (Shop around; prices vary a lot). Greens absolutely thrive under this light. It uses the same bulbs as the fixtures above, so I only have to keep one kind of replacement bulb on hand. Bulbs last a couple years, but not “10,000 hours” as advertised.

The Agrobrite has an amazingly reflective fixture. This planter is close to 20 years old but you can still find find similar things.
Monios T8 LEDs. There are many brands of this style light; I don’t see much difference among them.

I’ve started adding in much cheaper LED lights (Monios T8 LEDs, both 2′ and 4′ in full-spectrum and cool 6500K versions). These are very convenient and modular. You can hang them horizontally or vertically; you can screw their clips into wood or use the attached hooks; you can daisy-chain them in lots of configurations. They are sufficient as supplemental light, or as primary lights if you put them close enough together (like, 6″ apart).

Whatever you buy, BE SURE it includes reflectors. Having some sort of reflection increases their light output by at least 5x (as measured by my light meter phone app – “Korona”). Since mine didn’t come with reflectors, I’ve been improvising with aluminum foil, aluminum flashing, and mylar reflective sheeting. It’s more expensive and uglier, but it really helps. The really wild thing is that I learned this reflection setup (below) actually reflects more sunlight around to the back of this vertical planter than the LED lights produce. Mind. Blown.

Greenstalk planter, Monios T8 LED lights, Mylar reflective sheeting, and curved wire trellis. The Mylar reflects more light (sun coming through the windows) than the LEDs produce!

Deep Dirt

Unless you are growing microgreens, you really need a lot of dirt to grow food in pots. One head of lettuce needs a pot at least 4″x4″x6″. I really like growing lettuce in clear plastic “shoe boxes” – two or three heads per box. Three boxes fix perfectly under a 2′ grow light. I’ve also just discovered, thanks to my neighbor’s excellent discard pile, that these Hefty 8.5 gallon under-bed boxes are absolutely perfect for growing baby greens. Again, they fit perfectly under the 2′ grow lights, and they are sturdy enough to move when full. I didn’t even drill drainage in these – I can see the water level and not over-water them. And at about $10 each, they are a steal compared to most flower pots. Whatever you get, make sure it’s at least 6″ deep.

Check out that root system!

I’ve also been trying the original Greenstalk vertical planter. There are lots of planters in this stackable style; I picked this one because it holds a whole cubic foot of dirt per tier. You really want that root space. They have a new version called the “Leaf,” which has shallower tiers. This might work for indoor greens just fine. If you get one, definitely get the “mover” wheeled base – you are going to want to rotate this frequently. I had mixed luck with it over the summer, but I think I had too little light and was trying to grow the wrong things – beans and carrots, which didn’t take off as I’d hoped. I’m trying it this fall with kale, tatsoi, lettuce, and chard; we’ll see how it does now that I have lights added to the setup.

What else? Random planters I originally bought for outdoor use, each of which holds maybe 3 cubic feet of soil. They all purport to be self-watering; that’s bunk. The rolling cedar ones I ended up lining with plastic (heavy-duty garbage bags) because they had huge gaps and they leaked when I watered them. But that’s working fine now, and I was able to set up a second tier underneath by suspending two of the LED lights from the bottom and putting a 13 gallon under-bed box on the floor. That bit is new, but it seems to be doing well.

I’ve rigged several LED lights around this setup: two 2′ lights hanging underneath and 4′ lights above and resting on the edge facing in toward the plants to balance the light from the window. The top lights use shower curtain clips on a curtain rod. Note the homemade reflectors.

I also have some random plant pots, window boxes, and such. My rule of thumb is “at least 6″ deep” or “at least 2 gallons.” One or two chard or kale plants can grow to full size in a 2-3 gallon pot.

Chard that I brought in from the garden at the end of the season. The yellow one is going into its second winter.

What kind of soil do you use o grow greens indoors? Something with good drainage and lots of fertility. I tend to go with bagged stuff rather than homemade compost to try to keep the bugs out of my house. Happy Frog is pricey, but good. You can mix your own, but the price ends up being about the same in the end. You’ll want to tend that soil well, because it’s your big recurring expense. To that end…

Yes, you actually need fertilizer

I’m so accustomed to how I handle soil fertility in the garden, it’s been a long time coming around to accepting that I need to buy something called fertilizer and use it regularly. When confined to pots, plants just eat up all the nutrients in soil really fast, and then they just…stop growing. They don’t die, but they don’t thrive, either.

Worm castings are good, but pretty low-powered. I bought some kind of organic granules at a hydroponic shop, but I’m wishing now I’d gotten liquid fertilizer (especially for the Greenstalk). But I have a big bag of it, so I just put it in a shaker bottle and shake some on and water it in each time I harvest greens. I’m not an expert on fertilizer, so I went by what the knowledgeable folks at the store said was good for growing leafies. When I take plants out (e.g., the lettuce goes bitter after about 3 pickings), I do a heavy rejuvenation of the soil by adding vitamins (worm castings and the powdered fertilizer) and minerals (green sand and/or bone meal). After 2-3 rounds, or if the soil seems to be tiring out, I dump it in my garden and start with fresh dirt. That’s really a pain (and expensive), so I’m trying to get better about rebuilding the indoor soil.

Wow, that sounds expensive

Um, yeah. You’re not going to save any money by growing greens indoors. You can cut corners on containers for sure, and on lights if you rig your own stands and reflectors. You might be able to come up with a cheaper way to do the soil, too. Microgreens need almost nothing in the way of soil and light, so start there if you’re looking to economize. I did my setup this way because this is my hobby, and looks were moderately important (most of my lights are in my living room most of the year), and I was willing to pay for that. I don’t expect to make my money back in cash saved at the grocery store – though I’m ramping up enough this year that may be a factor. And, with Covid, access could be an issue. But this setup pays me back in joy every day, and that ain’t nothing.

Published by Emily

I'm an instructional designer and gardener based in Ann Arbor, Michigan. Free moments find me in my garden or the forest, hugging trees and all that jazz.

3 thoughts on “Growing Greens Indoors

  1. Dyna-Gro Foliage-Pro for winter fertigation / foliar feeding. Google “Al’s gritty mix” (originally of Gardenweb fame)… I follow his regimen for my potted woodies. Al is a local guy by the way. Y’all should really repot that poor lemon tree 😉

      1. Hey Emily! Sorry for the late reply, I don’t drop by here too often.

        I just potted up my other (similar vintage) citrus trees into 4.5 gallon pots. Of course you can restrict root volume if you want to keep them on the small side, but they are seedlings and will want to get big. I use the gritty mix, it’s basically a bonsai mix… equal parts by volume of chicken grit, pine bark fines and Turface all screened to a uniform particle size. Citrus will also benefit from some chelated iron a couple of times per year.

        Foliar feeds vary… usually they are safe to use within a day or two of harvest. Foliage Pro can be used on vegetables, but I have only used it on my potted woodies and I only do that during winter. Most of the plant nutrition in the FP regimen comes from the root drench / fertigation at a constant low level of concentration (it’s only 9-3-6 and I use maybe a teaspoon per gallon). Leaves don’t really absorb a lot of nutrients, so it’s more like fertigation with some incidental foliar feeding.

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