It grows quickly, is super nutritious, and is Popeye’s food of choice. What’s not to love about spinach? Spinach is one of the most nutrient dense vegetables you can grow, with more protein, minerals, and vitamins than any other leafy green vegetable.
Spinach is also an easy vegetable to grow indoors and does extremely well in containers. It also has moderate light requirements and only needs a modest amount of high nitrogen fertilizer. Growing indoors means you can have a longer growing season since spinach doesn’t grow well in the high heat of summer.
Benefits of Growing Spinach Indoors
Health benefits of spinach aside (that’s a whole other article by itself), there are several good reasons to start growing spinach indoors.
If you don’t have the space for a garden outside, you can grow a lot of spinach easily indoors. They don’t have high light requirements and don’t need a lot of space to grow. More on that later.
Even if you have a garden outside, you should consider growing spinach indoors as well. As previously mentioned, spinach naturally grows well in cool environments. If exposed to the summer heat, they can easily bolt (produce a flower stalk) which makes the leaves taste extremely bitter. Even if you grow it as a spring crop, if you have short springs, you might get a couple weeks of harvests before they bolt, then you have to wait until maybe September to plant them again.
Planting in a container indoors means your spinach will only be exposed to warm, but not hot, temperatures and take longer to bolt. And if you have a cool place like a basement, that’s even better. Some people grow spinach all summer long under lights in their basement.
And if you live in a climate with cold winters, you can grow a supply of fresh spinach indoors throughout the winter months.
Container and Spacing Requirements for Indoor Spinach
Spinach grows readily in containers and doesn’t have very strict space requirements. Having relatively shallow roots, you can get away with a container as deep as 6 to 8 inches (15 to 20 cm). A deeper pot can let your potting mix hold on to more moisture, but this is less important indoors as evaporation doesn’t occur as quickly as when you’re growing spinach outdoors.
How much you space your spinach also depends on how large you want your spinach plants to grow. For large, full-sized spinach, you should grow them about 5 inches (13 cm) apart. However, you can plant them closer for medium-sized spinach leaves. According to square foot gardening guidelines, you could plant 9 spinach plants within a square foot space (for a round pot, that means an effective diameter of around 14 inches).
I personally go for three to four spinach plants in a 2-gallon container and around six plants in a 5-gallon container.
For baby spinach, you can space them as close as 2 inches apart.
Using Grow Lights to Grow Spinach Indoors
Although spinach does not have very high light requirements, you won’t get very good results growing spinach on a windowsill. That said, spinach can grow next to a south-facing window, but it might grow more slowly and be more leggy.
Ideally, you should grow spinach under grow lights. As a leafy vegetable, spinach can thrive under T5 fluorescent bulbs or CFL grow lights, but for greater energy efficiency, I lean toward LED grow lights. Never buy an expensive LED grow light for small-scale home gardening–it’s not necessary. You can pick up some good LED bulbs for as low as $25-30, but my personal favorite is the SANSI 36W grow light, which is more than enough to grow a 5-gallon container full of spinach, or three 2- or 3-gallon containers in a 2×2-ft (60×60-cm) area.
Whether you’re using fluorescent or LED grow lights, when your plants are small, you should place your lights close to the top of your spinach to avoid leggy plants, but at least 3 to 5 inches away so they don’t overheat.
Spinach can grow surprisingly fast once it starts putting on more leaves, so check regularly to make sure your plants aren’t growing into the lights, and use your intuition to adjust the distance. I learned this the hard way with an indoor pepper plant that had its growing tip touching the grow light and the leaves ended up bleached white and crispy.
As for how long to keep your lights on, I’ve had success with at least 12 hours of light per day, up to 18 hours. Although more light means more energy which means faster growth, a period of darkness is important for plant development. If you have good lighting, you can shorten the light period to 6-8 hours, but your spinach will grow more slowly.
Watering and Fertilizing Your Indoor Spinach
Spinach doesn’t like wet feet, nor does it like drying out. When any seedlings are small, it’s a good rule of thumb to keep the soil evenly moist (but not soaking wet) while the roots get established.
For mature plants, I water whenever the top inch or so of my soil is dry. If you forget to water your spinach plants and they start wilting, give them a good watering and they will bounce back. But keep in mind the stress from a lack of water could trigger your spinach plants to bolt early, leading to bitter spinach.
Despite being such a nutrient-dense vegetable, spinach is similar to other leafy green vegetables in that it doesn’t need any special fertilizers, and can thrive with a well-balanced, all-purpose fertilizer. If you want to give your spinach the best chance for success, use a fertilizer with higher nitrogen (the N in NPK numbers).
You can use a slow-release fertilizer on planting or feed your spinach with liquid fertilizer every 7 to 14 days once they start getting bigger. I’ve only used liquid fertilizer for indoor spinach (hydroponic nutrients or just regular MiracleGro) but if I were going to use a slow-release fertilizer, I’d probably go with Jobe’s spikes or some other granules. Spinach is not picky!
How to Harvest Spinach Grown Indoors
Spinach is similar to other leafy green vegetables (lettuce, kale, mustard, Swiss chard, etc.) in that it’s best to harvest it using the cut-and-come-again method. This method involves cutting off the lower leaves first, leaving some leaves on top and the central growing tip to continue developing new leaves. There’s really nothing to it.
Spinach can be harvested at any stage. You can wait until the leaves get large and thick, or you can harvest the small leaves as baby spinach.