How to grow stevia in a greenhouse

How To Grow Stevia In a Greenhouse | Ultimate Guide

Stevia is a herb grown in tropical climates for it’s ultra sweet, low calorie leaves.  The leaves can be dried and used as a sweetener in drinks as well as directly in cooking.

Stevia is a tender perennial however, as it requires a warm environment, it’s usually grown as an annual  from seed.

As germination for Stevia seeds can be tricky, propagating multiple plants from an adult plant is sometimes easier.

Either way, Stevia is ideal for the hot greenhouse environment, so we’ve put together the ultimate guide on how to grow this fantastic plant.

SowTransplantSpacePlant careHarvestSeason
Mid Apr – Early MaySow into seed tray. Transplant to small pots.50cmKeep warm in full sun.60 daysAug – Oct

7 plants should be enough to use as a sugar replacement.  A teaspoon of dried stevia plant is the equivalent sweetness of 8 teaspoons of granulated sugar.

Sowing Stevia

Stevia can be sowed directly into a seed tray or set of small 7cm pot.  Steviacan be tricky to germinate so it is probably best to sow 10 times as many seeds as what you are hoping to eventually plant up.

You can sow up to 10 seeds per 7cm pot.

Stevia should be sowed in mid April to early May (late April ideally), so that the general outdoor temperature is fairly high.

So how do you sow stevia?  Follow these simple steps.

  1. Fill a seed tray with potting compost.
  2. Water the tray with a watering can with a fine rose. Watering at this stage will mean that you won’t run the risk of washing the seeds to the corners of the tray later.
  3. Make a series of holes in the compost, about 0.5cm deep.
  4. Pop one seed into the hole.  How many you sow is up to you however due to the low germination rate, sow more than what you need just in case some seeds don’t germinate into seedlings.
  5. Lightly sprinkle a thin layer of potting compost over the seed tray (a few millimetres is fine). This task will be easier if you use a garden sieve.
  6. Gently press down the top of the compost to ensure that the seeds are making good contact with the soil.
  7. Lightly water the tray once again.
  8. Place the tray in a warm, sunny spot and try to maintain a temperature of 68F to 70F (20C – 21C).  A heated propagator or mat might make this easier.

Keep the compost moist while the seeds germinate. Your seedlings will germinate within 21 days.

Transplanting Stevia

Once the “true leaves” have appeared on the plant, transplant the stevia plants to individual 7cm pots.  This should be approximately 14 days after germination.

True leaves are the leaves that look more like the actual plant leaves rather than the seedling leaves. They are usually the second or third set of leaves to start growing on a seedling.

  1. Fill some 7cm pots with one part vermiculite to 5 parts general purpose compost.
  2. Use a pen or pencil to create a small hole in compost ready for the new seedling.
  3. Gently remove a seedling from the seed tray taking care not to damage the root of the stevia plant. Use the pen or pencil to tease out the seedling.
  4. Place the seedling into the hole of the 7cm pot so that the seedling leaf is just above the soil surface.
  5. Water the pot thoroughly.

If you are propagating a set of stevia plants from a single adult stevia plant that was bought from a shop or over wintered in your heated greenhouse, follow these steps:

  1. Find a stem approximately 10-15cm long.
  2. Remove the entire stem from the adult plant by gently twisting it off my hand.  This should leave the heel of the stem on the propagated stem.
  3. Remove the bottom hal;f of leaves from the stem.
  4. Bury the stem up to the first leaf.
  5. Keep watered and position in a warm part of the greenhouse.

Planting Stevia in a Greenhouse

Once the risk of any frosts has gone and temperatures are consistently above 68F, you can look to plant your stevia plants.  This will likely be around early June.

Stevia can be planted directly into a greenhouse bed or 12 inch container.

Spacing Stevia

You should give your stavia plants 50cm of space to grow into.

Expect the plant to grow between 1ft and 3ft tall so ensure that there is sufficient height room for it to grow into in your greenhouse.

Soil & Location in a Greenhouse

Stevia prefers a nutrient rich, loamy but well drained soil.  It might be worth adding some horticultural grit or vermiculite to open up the soil and increase the drainage.

Ideally, the soil should be between 6.5 and 7 Ph.

Stevia should be planted in a full sun position however, they can tolerate partial shade.

How To Care For Your Stevia Plants in a Greenhouse

Stevia doesn’t require much care once planted into their final position or container.  There are two main things to consider:

  1. Watering.
  2. Feeding.

Watering Stevia

Stevia plants don’t require excessive amounts of water.  Just keep the roots damp and don’t allow them to dry out.

A good indication of when a stevia plant needs watering is when the top inch of the soil has become dry.

Feeding stevia

Once your plant is actively growing and maturing, apply a well balanced water soluble fertilizer to your stevia every 30 days.

Begin this application in early July.

The fertilizer should contain no more than between 6-10% nitrogen.  Too much nitrogen can have a detrimental effect to the taste of the leaves.

When To Harvest Stevia

Harvest stevia leavesBegin to harvest the plant in mid-late summer when the leaves are large enough to use.  This is likely to occur 40-60 days after transplanting or 90-100 days after germination.

Harvest entire stems however, don’t completely defoliate the plant in one go.

Harvesting can likely continue up until the fall, however as soon as nighttime temperatures drop below 50F (10C) the plant will deterioate quickly.

It is possible to extend the growing season of stevia in a heated greenhouse.

To dry the leaves, tie a small bunch of stems and hang them upside down in a cool, well ventilated room. 

Once the leaves have dried, grind the leaves up into a fine powder.  You can use a food processor or pestle and mortar to do this.

Store the powder in air tight container.

Common Stevia problems in a Greenhouse

Stevias don’t suffer from any particular pests or diseases.  

There are two main things to look out for when caring for your stevia plants:

  1. Plant wilt.
  2. Flower stems.

Plant wilt

Don’t over water your stevia.  Applying too much water to a stevia will cause the plant to wilt.

Once wilting has occurred, the plant probably won’t recover from this.

Flower stems

Stevia flower stemAs the summer months progress, your stevia plant will likely begin to develop flower stems.

These stems can have a detrimental effect on the taste of the leaves so keep an eye on them and remove any flower stems that appear as soon as possible.

Stevia Greenhouse Growers Kit List

We have selected a kit list of key equipment and tools to get you growing tasty stevia plants in your greenhouse in no time.  All of the items below are links to products available on Amazon giving you the added convenience of home delivery.

Seed propagation tray

Garden sieve

Seedling sower dibber

Stevia seeds

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