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How long does it take to grow stevia from seed?
A question we often hear so we decided to answer it with a walk-though of the entire germination process.
Considered a tender perennial herb, stevia (Stevia rebaudiana) can be grown outdoors in U.S. Department of Agriculture plant hardiness zones 9 through 11 (find your zone by entering your ZIP Code, here).
The plant’s leaves contain a compound called steviol glycosides which is used to manufacture a sweetener with zero calories.
Because the levels of these compounds vary in plants grown from seed, you may have one plant with quite a lot of sweetness in its leaves and another plant with leaves that have very little.
Another problem with growing stevia from seed is that it doesn’t’ readily germinate. With careful choosing, planting, nurturing and lots of patience, however, you may be able to grow several stevia plants successfully from seed.
Soil and Container for Stevia Seeds
Stevia seeds require consistently moist, very warm soil to germinate and they will rot if the soil is wet and cold.
Use a soilless seed-starting mix to avoid fungal pathogens that might be present in garden and even potting soil. See the Resources at the end of this post for recommendations.
Any container can be used to grow stevia from seed, as long as it has holes in the bottom to allow excess water to drain. Because the seeds require humidity to germinate, consider using a flat with a plastic dome, such as the one listed in the Resources section.
The soil must remain loose, so don’t pack it down as you fill the container with soil.
Stevia Seed Planting Procedure
These seeds are so tiny! And there is something very important you need to know about them, especially when purchasing online. Before paying for the seeds, ask the seller what color they are.
Why?
Read any review section on Etsy or Amazon and you’ll find that stevia seeds get a bad rap for being hard to germinate. The truth is, however, that it’s not the seed and it’s not the gardener, but the ignorance of the seed seller.
According to a rigorous study by Jeffrey Goettemoeller and Alejandro Ching, “… viability of black seed … was much higher than tan seed, 76.7 vs. 8.3%” (“Seed Germination in Stevia rebaudiana,” reprinted from the book “Perspectives on new crops and new uses,” 1991).
Viable stevia seeds are black. So don’t even bother with seed that is tan, white, off-white or clear. In fact, ensure that the seller accepts returns before purchasing and then send them back if you don’t get black seeds.
Lay the remaining stevia seeds on their sides on top of moist planting mix, and barely (some growers don’t even cover theirs) cover them with sand or vermiculite.
Squirt the covering layer with water from a spray bottle to settle the stevia seeds into the mix without washing them away.
When the soil begins to dry during the germination process, place the planting container in a shallow pan, and fill the pan with water until it reaches halfway up the container’s sides. Remove the container from the water when the top of the soil is moist.
Stevia Seed Germination Period
The soil must remain 70 to 75 degrees Fahrenheit for the stevia seeds to germinate. Planting unviable seeds and the temperature requirement are critical steps that so many home growers miss.
To achieve the heat requirement, place the germination container on a heat mat.
Insert a soil thermometer into the container, so that you can monitor the temperature and make adjustments as needed. You’ll find an excellent soil thermometer at Amazon.com.
Adjust the temperature by using the heat mat’s thermostat.
Place fluorescent lights 6 inches above the humidity dome and allow the lights to run for at least 12 hours per day.
Care of Stevia Seedlings
Stevia seedlings grow slowly and take about two months to grow to a size at which it’s safe to transplant them. In the meantime, give the stevia seedlings six to eight hours of sunlight per day, and keep their potting mix moist.
Wait until they have their third or fourth set of leaves before transplanting each seedling into its own, small planting pot. They should stay in those pots until they’re ready to be planted outside – after all danger of frost has passed and the soil temperature outdoors is at least 65 degrees Fahrenheit.
As they grow larger, and have several branches, start pinching the tips of the branches. This will prompt the stevia plant to grow bushier.
Resources
Stevia rebaudiana ‘Candy’ Organic Seeds
