Growing Stevia

Latest Update 31st July 2016.

Stevia
  • Stevia is a herbaceous perennial and is grown as a culinary herb.
  • It needs full sun and grows to 1m tall.
  • It is a powerful sweetener and its leaves can be used in confectionery and drinks.
  • They can be used freshly chopped or dried.
  • With the current issues associated with over-consumption of refined sugar, Stevia seems like a useful alternative.
  • 3-4 teaspoons of dried Stevia leaves are said to produce the same sweetness as a cup of refined sugar.  
  • Stevia can be grown from seeds although I have found them difficult to germinate.
  • Cuttings strike readily and can be taken during summer.
  • I haven't really explored Stevia's benefits yet, last year was my first attempt at growing it, and the surviving plant has died back for winter.  I hope to spend some time evaluating it in the coming season.
Details.
  • Binomial name:                                             Stevia rebaudiana
  • Family:                                                         Asteraceae.
  • Garden bed type:                                           Drip Irrigated Bed.
  • Recommended soil pH:                                  5.0 - 7.5.
  • Plant size:                                                    Up to 1m tall.
  • Plant spacings (centres):                               300mm.
  • Climate:                                                       Warm temperate.
  • Geographic hemisphere:                                Southern. 

Nutrition 
  • The active sweetener in Stevia leaves is Stevioside which is a glucoside.  It is not a carbohydrate and is very low in calories.  Its soluble in water, does not ferment, is not toxic and leaves no aftertaste.  It is thought to be a safe organic alternative to sugar in our diet.
Growing Conditions.
  • Stevia needs full sun
  • It dies back in winter usually back to the crown and sends up new growth in spring.
  • It tolerates slightly acidic soil, and grows well in rich organic soil.
Soil Preparation.
  • In September, clear a space for Stevia in a drip irrigated garden bed and add a 60mm layer of homemade compost.  Cover with a 50mm layer of straw mulch.
  • Leave the bed for 4 weeks to build up worm and microbial activity.  Move the mulch to one side before planting.
Growing Instructions.
  • Sow Stevia seeds in August on the surface of an organic seed growing mix in a mini pot.
  • Soak the mini pot for an hour in a tray containing 10mm of water (preferably rainwater).  The water will move up into the soil without flooding it. 
  • Sink the mini pot 15mm deep in a propagator.  This will keep the soil moist until the seedlings are ready to transplant.  Protect the seedlings against frost. 
  • After 4 weeks transplant the seedlings individually into organic potting mix in mini pots and returned to the propagator.
  • After a further 4 weeks plant the seedlings in the prepared bed 500mm apart.
  • Return the mulch once the stevia is established.
  • If propagating from cuttings take a vigorously growing stem about 100mm long and strip off all but the top cluster of small leaves and shoots.  
  • Plant the cutting in the compost media of the propagator and water it in using dilute seaweed extract.  Leave it until the cutting resumes growth and has at least doubled its height above the soil. 
  • Plant the mature cutting in the prepared bed and water it in well with dilute seaweed extract (suppliers directions).
  • Apply a foliar spray of aerated compost tea every 4 weeks when the other edible plants are sprayed.
Harvesting and Storage 
  • Stevia leaves can be harvested green at any time during the growing season, but if you want to dry them, its best to wait until late summer just before the plant flowers and hang the harvested stalks upside down in bunches in a sheltered place to dry.
  • Once they are dry, strip the leaves off the stalks, crush them and store them in a clean dry airtight jar for future use.
Organic Pest Control.
    • Stevia needs protection against slugs and snails, so use self adhesive copper tape around the base of the bed to keep them out.
  • Greenhouse whitefly.  
    • Aerated compost tea improves the plant's resistance to whitefly damage.
    • Exclusion netting is very effective against whitefly, but they are very small and will occasionally breach your defences, so you will need to check your crop regularly.  
    • Control any infestations by spraying your crop thoroughly with organic horticultural oil (Eco-oil in Australia).
    • Spray again in a few days to ensure second generation whitefly do not survive.
  • Aphids (greenfly). 
    • Use the same method described above for whitefly.
  • General.
    • Repeated foliar sprays of aerated compost tea should deter most airborne pests and diseases.
    • Proper soil preparation and regular applications of home made compost should control soil borne pests.