Growing soil sprouts runs counter to much of what I always held true about gardening in general. When I try to explain soil sprouts to my farming friends and gardening buddies, they often have trouble understanding the concept at first. I know what bothers them: They think that if they plant 70 sunflower seeds or 150 broccoli seeds, their crop will be enormous compared to the tray of greens I describe.
“It is so seed intensive,” one farmer complained. He thought too many seeds were required so he dismissed the idea. He reasoned that one mature sunflower could produce easily hundreds of seeds, or each full-grown plant a large head of broccoli. Why harvest the sprouts before they’ve had a chance to produce their full yield?
But when you look at it in a different light, it makes sense. No one would call it “seed intensive” to grind up wheat berries or corn kernels— which are viable seeds—to make bread or object to boiling rice to make dinner. Soil sprouts are just another way—a different way—to eat seeds. Rather than grinding or boiling I grow them for a short time.
The general principle of growing soil sprouts has been understood in Asia and elsewhere for many centuries. 17th century Italy employed radish sprouts, and the English have used cress sprouts for many years. Rich in vitamin C, cress sprouts helped sailors to combat scurvy on long voyages.
Many of the seed varieties that I grow for greens wouldn’t be used as food themselves, like radish seeds and broccoli seeds. With my methods, seeds that could only be planted in the outdoor garden in the past can now be used to grow fresh greens indoors. They’ve found a useful place in the pantry as winter food.
An indoor salad garden can even work as a full-time garden for those who live in apartments or condominiums with no other place to grow their own food.
Indoor gardening takes a different approach
The techniques that work for an indoor salad garden of soil sprouts are not the same as those I use for my earth garden. An indoor garden required an entirely different approach. For instance, instead of watering the seeds after planting, as I would normally do in my earth garden, I water the seeds before planting by soaking them. Where I usually plant seeds in the soil outdoors, for soil sprouts I scatter the seeds on top of the soil indoors. In my outdoor garden, seeds are planted in carefully spaced patterns. For my indoor garden’s soil sprouts, I spread the soaked seeds on top of the soil so close together that the seeds touch.
Normally gardeners take pains to provide plenty of light for young plant starts, providing grow lights from the moment the new plants emerge from the soil. It’s a totally opposite approach for soil sprouts; I start them in the dark for four days.
For the experienced gardener, it’s a bit of a challenge to go against the grain of years of gardening outdoors. I know it was for me. If this is your first garden and it’s all new, you don’t have the “this-is-how-I-usually-do-it” attitude to overcome. But I should give you fair warning that if your expert gardener friends tell you you’re doing it all wrong, they would be right—that is, if you were growing outdoors!
Just be patient and invite them over for a fresh salad sometime in January, when they’re frozen out of their own gardens.
- Soak the seeds first
Presoaking gives the seeds a jumpstart before planting. Usually seeds must soak up enough water from the soil to initiate growth. Depending on the environment it might take days before the seeds even begin to sprout. Although soaking is common to hasten the process of growth for large seeds, with soil sprouts all of the seeds are soaked first, regardless of size. This step is a key to realizing the fast growth found in indoor salad gardening.
I’m always excited by the miracle I witness each time I soak them for another batch of sprouts. As soon as I pour the water onto the seeds, it’s off to the races, with all the potential in those little “horses” galloping to the finish line—I can almost hear the cheers!
My top seed choices: sunflowers, peas, broccoli family, buckwheat and radishes. Soak 6-12 hours.
- Plant on top of the soil
Use standard germination mix. (A 20-quart bag costs around $15-20.) To be perfectly accurate, there is no actual soil in this “soil.” You do not need containers with drainage holes—cereal bowls will do. Pre-mix a gallon of “soil” with four cups of water.
Planting the seed on top of the soil also saves a day or two because the stem and leaf don’t have to push up through the soil. It also prevents the seed hull and leaves from being covered in soil and keeps the sprout cleaner. Cleaner stems and leaves (in addition to the soilless seed-starting mix) mean there’s less chance the plants will develop damp off (a disease that quickly kills young shoots) or molds, and the greens are easy to clean at harvest time.
- Seeds are touching
Outside, I would need a 50-foot garden row to plant the same tablespoon of sunflower seeds that I use inside in a small tray that’s only 1⁄8 of 1 square foot in size. By planting the seeds so close that they touch, I get the maximum possible harvest of greens from the smallest possible area. The seed has only enough room to send a root down into the soil and a stem up toward the light, but this is entirely adequate for the short “growing season” of shoots.
- Grow in the dark
For my traditional garden, I use lights and a cold frame or a greenhouse to give young plants plenty of light in the early stages. But soil sprouts are grown for the stem and first leaves of the plant only, and the first few days of darkness encourage a long stem to grow by “forcing” the seed to search for light.
Outdoors, in more hostile conditions, a seed stem may have to make its way through a pile of leaves or straw before it comes out of the dark. The simulated darkness of a tray with paper covers takes advantage of this natural urge in plants to search for light. It encourages a very productive harvest. Total darkness isn’t necessary; even low-light conditions will do the job of forcing the sprouting seeds to develop long stems in the first stages of growth.
- Plant every day
In my outdoor earth garden I typically plant varieties like tomatoes or squash once per season. For vegetables like lettuce and carrots I do a second planting at mid-season to harvest a fall crop. For varieties like radishes I replant every two weeks and enjoy a steady supply of fresh roots all growing season. With soil sprouts I plant every day.
For a steady supply of greens from my indoor salad garden, planting every day is key. I routinely start small batches of seeds, about five tablespoons (74 ml) spread over five trays each day. So every day, seeds planted a week ago are coming to harvest. I know just how many trays I’ll need, week to week, harvesting just what I need each time. I want my indoor salad garden to remain small and manageable.
- Harvest more
My objective when growing sprouts in soil is to encourage rapid growth of the stem and a large seed leaf (called a cotyledon). This allows me to harvest nearly all of the stored nutrition from the seed. The soil sprouts are generally about six to eight inches when I harvest them—considerably longer than regular sprouts and microgreens.
The nutritional value is immense, as well: One ounce of the broccoli family sprouts (Chinese cabbage, purple kohlrabi, broccoli, etc.) has as much of the anti-cancer compound sulforaphane as four pounds of fresh broccoli.
I’ve learned a lot about seeds and sets from growing soil sprouts; in fact some of the techniques I’ve put to good use in my outdoor garden, too. Take peas, for instance. An early, wet spring can make for patchy germination at best, and other times the peas just rot in the soil. One early spring day a few years ago, I realized that I had all these hale and hearty pea sprouts growing indoors in trays. I transplanted some outdoors. They had no trouble growing perfectly well, with no setback effect from transplanting, even though garden books typically advise that peas do not transplant well!
Sometimes going against the grain, stepping outside the box and doing something counterintuitive, offers rich rewards. Growing soil sprouts is one of those times.
Adapted from Year-Round Indoor Salad Gardening: How to Grow Nutrient-Dense, Soil-Sprouted Greens in Less Than 2010 Days (2015: Chelsea Green; $30). For more details, listen to an interview with Burke and Bryan Earl on Utah Public Radio’s “Zesty Garden”: http://upr.org/post/zesty-garden-october-22.