Propagation and Container Growing
Stevia stem cuttings root easily without hormones, but only under long day conditions. A fluorescent shop or plant growth light both work well. Leave the light on 14 to 16 hours per day, 5 to 9 inches above the cuttings. An automatic timer will make the job easier. Even with artificial light, Stevia cuttings root most easily during the long days of spring. Cuttings should be taken in March for transplanting in May or June. Plants from later cuttings may be over-wintered in pots under fluorescent lights.
Fall cuttings root successfully with the use of rooting hormones. Use a low-strength rooting compound available from garden retailers or make your own natural compound with Steve Marsden's recipe. Harvest a handful of willow branch tips and remove the foliage, then liquefy in a blender with twice the volume of water. Dip cuttings in this mixture before placing in the rooting medium.
Coarse or medium grade horticultural vermiculite works well for rooting Stevia. Mr. Marsden prefers a peat-lite mix that includes bark, especially for outdoor propagation beds. Coarse, clean sand may be used as well. Place small pots, or cell packs with drainage holes, in flats or trays to facilitate watering from below as needed. With a sharp blade or pruning tool, make cuttings 2 to 4 inches long. Each cutting should have 2 or 3 nodes. A node is where leaves attach to the stem. Cut between, rather than at the nodes. (Sumida, 1980). Plunge the proximal end (closest to the roots on the mother plant) of the cutting into the rooting medium far enough so that at least one node is buried and at least one node remains above the surface. Remove all leaves from buried nodes. Above the surface, remove large leaves by cutting or pinching leaf stems, taking care not to damage the tiny axillary leaves emerging behind large leaves. These axillary leaves are the growing points of your new plant. Keep cuttings at 60 F to 70 F. Indoors, under lights, misting is not necessary. Outdoors, or in a sunlit greenhouse, cuttings should be misted several times per day until roots are well formed. After about a week, growth should be evident if rooting was successful. After 3 to 4 weeks, transfer plants to larger pots (at least 3-4 inches in diameter) with standard potting soil. Transplant these to the garden in another 2 to 4 weeks or keep as a container plant.
For older plants, keep the fluorescent light a few inches above the foliage. When stems reach 7 to 10 inches in length, cut them back to promote branching and vigor. Over-wintered plants look devitalized by the end of the winter, but regain vigor when transplanted outdoors. Some plants will inevitably be lost, so grow more than you think you'll need. Stevia may also be grown outdoors in containers such as gallon pots. If you start with a high-quality potting soil that has organic fertilizers mixed in, further fertilization may be unnecessary, but a monthly watering with a dilute seaweed solution can be beneficial. Mr. Langan recommends a balanced, slow release fertilizer applied every two weeks for container plants. He also advises using wooden containers or the double pot method to insulate roots from summer heat. Place in full sun when it's cool, but provide shade during hot weather, making sure the soil doesn't dry out. For perennial production, bring containers indoors before the first frost.
In garden: prefers moist, well-draining soil, slightly acidic. I have grown it in the Lockhart garden in a 3 inch layer of compost over clay soil with pH of 7.5. It did OK, but not great. Was killed by frost. Will try again this year in raised bed with sandy loam delivered from east of Bastrop. Did not do well in sand at Altamira -- probably got too dry.