Growing Vegetables Indoors Over the Winter: Not So Simple!

Don’t believe it when magazine articles and blogs promote growing vegetables indoors as something the average home gardener could do: it’s not easy, but instead very difficult. Photo: Kang Starr

As I write this in mid-fall, I’ve just leafed through yet another magazine article about easy it is to grow vegetables and herbs indoors over the winter. Pretty clearly, the writer never tried it. It was essentially nonsense: beautifully illustrated nonsense, but nonsense just the same.

Growing vegetables (and herbs) indoors is not easy, especially if by that you mean growing vegetables to full maturity. It’s damn hard! A challenge even for expert gardeners. And it’s expensive to boot! By the time you install the equipment necessary to really grow vegetables indoors, we’re talking $40 head lettuce plants. Ouch! 

Now, I’m not talking here about starting seeds indoors you’ll be planting outdoors later—that’s easy enough —, but rather vegetables you can really grow from seed to full maturity in your home during the dark days of fall and winter. The grocery list would ideally include tomatoes, peppers, lettuce, celery and others: the same veggies you normally grow outdoors during the summer. Is that even possible?

My answer is a very timid yes, but it isn’t going to be easy.

Fighting Mother Nature

The important thing to understand is that by forcing vegetables to grow under indoor conditions in the off-season, you’re fighting Mother Nature every step of the way. It’s like trying to raise fish on dry land and thinking you can do so just by spraying them regularly with water. Vegetables abhor short days, low light and dry air and so grow poorly, weakly and produce less. Insects and diseases, many that scarcely ever attack them outdoors, quickly move in: there’s nothing they like better plants suffering from severe trauma.

If growing vegetables indoors had been easy, we would have known about it long ago. Humans have been growing vegetables outdoors for at least 2,500 years. They were living in huts and log houses at the time, often right next to the vegetable garden, yet they never succeeded in growing vegetables indoors. I think it’s telling that a hundred generations of vegetable gardeners exclusively grew their vegetables outdoors.

One thing that 2,500 years of vegetable gardening has taught us all is that you get the best results when you give the plant what it wants. That works every time. Vegetables like growing outdoors in full sun (or nearly full sun) with plentiful moving air, regular rains, high atmospheric humidity and rich soil. And growing plants indoors—again, in fall and winter, when light is exceedingly rare and the air is desert dry—means putting plants in an environment where they don’t get what they want. It’s practically like plant torture.

Of course, I’m sure some readers will say, “What about those commercial greenhouses that grow tomatoes and peppers under glass?” Yeah, that works … but only because the greenhouse staff practically bends over backward to make the greenhouse environment as much like outdoor conditions as possible. They invest millions in making that happen, controlling every little aspect of care. I’m not sure you can turn your living room or basement into a reasonable facsimile of an outdoor vegetable garden with the kind of budget you’ll likely want to invest in it.

Lack of Light

The main limiting factor in growing vegetables indoors in the winter is light. Meeting the plants’ other needs is fairly simple. We already heat our homes and vegetables need about the same temperature as people. Watering is easy to organize (just don’t forget!), humidifiers are widely available to bring atmospheric humidity up and there is a wide range of soils, fertilizers, pots, etc. you can use. But where are you to get the intense sun that vegetables prefer?

That’s not a problem in the summer outdoors or even indoors in front of a large south-facing window at that season, but in autumn and winter, with their short, gray days and the sun’s reduced intensity? Just being behind a glass window that isn’t sparkling clean can reduce the light plants receive to half what they would get in summer. By mid-winter, as far as a tomato plant or a lettuce plant is concerned, a windowsill is pretty much as dark as Hades.

From Laidback to Excessive

A truly laidback gardener would simply grow their vegetables outdoors in the summer, the way Ma Nature intended it. But there are ways of growing vegetables indoors over the winter. Let’s look at them one by one, starting with the easiest methods and working towards the difficult (and expensive) ones.

1. Sprouts

Many vegetables and cereals are a snap to sprout as sprouts and the only equipment you need is a Mason jar and a piece of plastic mosquito screen. Plus, the technique is certainly simply enough.

Just pour about 1 or 2 tablespoons of seeds into the jar. Cover the opening with a piece of mosquito screen and hold it in place with the metal screw band of the lid (you won’t need the flat part of the lid). Now cover the seeds with 2 inches (5 cm) of cool water and soak overnight. In the morning, drain, then pour in more cool water, swish the seeds around to rinse them well, then drain again. From now on, twice a day, pour in enough cool water to cover the seeds, shake a bit, then drain well. Your sprouts will be ready in about 5 to 10 days (each type has its own schedule). You’ll know they’re ready when there are roots visible, but the first leaves (cotyledons) aren’t yet fully developed.

No light at all is needed at first, but after two or three days, a bit of natural sunlight will give greener sprouts with a stronger taste. You’ll have to experiment a bit on that level: some people find paler sprouts tastier than green ones.

Keep several sprouting jars going with various seeds at various stages of maturity so you’ll have something to harvest daily.

Why are sprouts so easy to grow? Because you harvest them at a very young stage, when they’re still living off the energy stored in the seed and before the lack of intense light harms them … and before anything has time to go wrong! 

You can read more about growing sprouts in this article: Sprouts: Fresh Home-Grown Greens All Year Long.

2. Microgreens

These are almost the same as sprouts, but you sow the seeds in soil … and harvest them a few days later than sprouts, in about two weeks, when the cotyledons (first leaves) are fully developed. For microgreens, more intense lighting is required or they will etiolate (stretch for the light), as they no longer rely totally on the energy stored in their seed. A place on a sunny window (winter sun does suffice) or under a fluorescent or LED lamp, for example, will be needed.

You can harvest microgreens with scissors, cutting them off at the base, or pull them out of the potting mix and rinse them well to remove any soil particles, as their roots are edible too.

You need to start new cultures every two weeks or so to always have fresh microgreens on hand through the fall, winter and early spring.

You can read more about growing your own microgreens here: Indoor Gardening All Year Long With Microgreens.

3. Salad Greens Under Artificial Light 

Leafy vegetables require less light than fruit-producing vegetables and root vegetables and ripen more rapidly. That means you can grow them indoors without too many complications. However, not in front of a window; at least, not in the fall or winter: there just won’t be enough light to grow healthy leaves. However, with a simple shop-type LED or fluorescent lamp suspended over a table or a shelf, you can grow leafy vegetables anywhere: in the basement, the attic, under a staircase, in a closet, etc.

You’ll need an inexpensive timer to make sure your plants get the light they need each day. I set mine to 14 to 16 hours to encourage a bit of extra growth.

Growing leafy vegetables under lights is certainly simple enough to do. Just fill pots or trays with moist soil (I prefer potting mixes that contain mycorrhizae, i.e. beneficial fungi) and sow the seeds about ½ to 1 inch apart (1–2 cm), barely covering them with mix. You can also use hydroponics and raise them without soil: that works too.

Adjust the height of the lamp so it is about 6 inches (15 cm) above the trays or pots. As the plants grow (and they’ll grow very quickly!), raise the lamp so it remains about 6 inches (15 cm) above the plants themselves.

Water as needed when the soil is dry to the touch, adding a little seaweed fertilizer to the irrigation water when you do.

How you maintain your plants as they grow depends on you, though.

Some gardeners like to grow their vegetables well spaced so each produces a nice individual rosette. If so, transplant the seedlings into individual 4- to 6-inch pots (10–15 cm) when their leaves start to touch. The maturity rate will vary, but, to give you an example, most lettuces will form a beautiful small but ready-to-harvest rosette in 40–60 days.

I prefer to harvest my greens without going through the hassle of transplanting. This close spacing gives a sort of hodgepodge of leaves where the individual plants aren’t too recognizable, but they will be ready to harvest sooner, in about 20 to 30 days, when they are about 6 inches (15 cm) tall. Just cut them about ½ inches (1 cm) from the ground … and let new leaves grow back. This “cut and come again” method normally gives a second harvest, sometimes even a third.

With either method, make successive plantings from early fall right through the winter so you’ll always have fresh salads to harvest right through until the outdoor gardening season begins.

You can grow most leafy vegetables following one or the other of the methods described. If you’re just starting out, I suggest trying mesclun (a mixture of greens): it will give you a bouquet of flavors in little space. Or sow individual varieties, such as lettuce (leaf lettuce grows the fastest), spinach, arugula, beet (for its leaves), etc. You can also grow several herbs this way, notably basil, coriander (cilantro) and parsley, although parsley is very slow growing.

As for root vegetables, the easiest to grow indoors is certainly the spring radish: just follow the method described above. For other root vegetables, use deeper pots, space the plants more carefully … and stick to baby vegetables: baby carrots, baby beets, etc.: they’re faster to mature. It isn’t as easy to grow full-size root vegetables in a pot!

Plus, for the serious gardeners willing to pay a fortune for homemade veggies, there are all kinds of even more specialized lighting systems using LED or fluorescent lights, from AeroGarden type systems with all sorts of sophisticated controls that give you a small quantity of very expensive greens right up to rotating light gardens that slowly spin around a light source, a system so sophisticated it will wow all your friends … but I’ll leave that to the fanatics!

To discover the wide range of possibilities, visit a hydroponics shop. There is certainly a hydroponics shop in your neighborhood.

4. Combine Sun and Artificial Light for Fruiting Vegetables

I’m not a great fan of growing fruiting vegetables (tomatoes, cucumbers, eggplants, beans, etc.) indoors for a winter harvest. They tend to be very tall, very needy plants that grow weakly when they don’t get enough light. Plus, they are slow to mature, taking months, not weeks like leafy vegetables … and the longer you grow a plant under less-than-ideal conditions, the more things are likely to go wrong. But if you insist on trying…

The cheapest way to go is combining natural sunlight and artificial lighting. You could, for example, hang a high intensity LED or fluorescent lamp over plants placed near the brightest window possible, raising the lamp as the plants grow (keep them about 6 inches/15 cm from the top of the plants). I suggest using dwarf varieties of fruiting vegetables, such as those designed for growing in patio pots: small determinate tomatoes, patio cucumbers, dwarf French beans, etc. That’s because adequately lighting tall plants under ordinary LED and fluorescent lamps is very difficult: usually only the upper leaves get enough light and, even with a window right nearby, the lower leaves struggle.

5. Grow Room

Or convert a room in your home into a grow room.

This is the same technology commonly used for growing marijuana indoors: 400- to 1000-watt high-intensity discharge lamps (HID lamps) installed on the ceiling providing light as close as possible to sunlight in intensity and in quality. This will likely require major modifications to your home: an additional electrical box, a special air conditioning system, a CO₂ generator, etc. Expect to pay handsomely just to get started … and there will be a big electric bill to pay every month as well. You can grow your veggies in potting soil or hydroponically: the choice is yours. As you can imagine, though, you’ll have to grow a lot of vegetables to make this veggie grow op worthwhile.

A Final Word

So, going back to our original question, about whether it is possible to grow vegetables in indoors even in winter… Yes, it is, but I still suggest sticking to sprouts, microgreens and leafy vegetables. Leave the fruiting veggies to real indoor vegetable gardening maniacs … or just wait until summer and grow them outdoors which is, after all, where they want to be!

Article adapted from one originally published on November 5, 2015.