Hardening Off in a Propagator

Once your plants have made it through winter, the time will come when they must leave the safety of their heated propagators and moved to their final growing place .

Before moving plants out of your heated propagator, you will need to harden them off. “Hardening off” is the process of acclimatising your plants to live outside of a heated environment, encouraging them to develop stronger, waxier leaves that can cope with natural conditions outside the propagator. This must be carried out gradually to avoid your plants going into shock.

You can start hardening off your plants when night time temperatures reach 5°C; although the higher the temperature, the easier the process will be. If hardening off at 5°C, you still need to implement some additional protection such as a frost protection fleece. A frost protection gardening fleece will keep the plant safe from any sudden drops in temperature and will allow you to plant outside sooner.


The decision for when to harden off plants should be based on the time of sowing/planting rather than the development stage of your plant. Young plants are less likely to tolerate sudden changes in temperature, so these should be left a little longer. Typically, when your plant has developed its true leaves it will be ready for hardening off.

Plants grown in warmer environments, such as an Electric Heated Propagator, will need to be hardened off more gradually, as these are used to higher temperatures.

The duration of the hardening off process can vary depending on what you are growing. However this is the typical process for hardening off in an electric heated propagator:

Stage 1: Leave the lid off your propagator during the day

Recommended Duration: 7 days

Stage 2: Leave the lid off your propagator all the time

Recommended Duration: 7 days

Stage 3: Remove plants from the propagator (ideally move to greenhouse or mini greenhouse, or outside with plant frost protection)

Recommended Duration: 7 days

Stage 4: Transplant your plants in their final planter


In addition to these steps, it is important to consider the other changes that your plant will have to adapt to and how you can prepare them for this.

- Your plants will be experiencing greater levels of direct sunlight, so try to move your plant to a sunnier spot gradually throughout this process to lessen the shock.

- Aim to plant out on an overcast day as this will minimise the risk of your plants wilting.

- If planting outdoors, protect young plants from slugs with some organic slug pellets and keep hungry pests away.

Now your plants will be ready to grow and your Vitopod Propagator will be free for sowing your springtime seedlings!

If you have any questions about hardening off, or if you’d like to share any advice from your previous experience, feel free to call us on 0845 602 3774 or email us at info@greenhousesensation.co.uk. Our Gardening Angels are always happy to help!

Quick Photo shoot

May is my favourite month in the greenhouse because it's full of promise with plenty of tomatoes and chillies setting, but I can still manage to manouvere around to take photos. Come July the yoga moves come in very handy to try to get whole plants in shot without tumbling over the tomatoes!

Anyway, here are a few photos.

Going Bananas



 The bananas in our greenhouse are receiving some tender loving care from Paul one of our expert greenhouse horticulturalists. 



Banana pup growing alongside mature banana

He has split a pup from one of the older plants and planted it into its own planter. A pup is effectively a banana cutting and it forms alongside the mature banana plant. We cut it when it' s 45cms tall, it’s quite a job because the trunk of the pup is 15cms wide.

 As with all cuttings it is very important to keep everything very clean when taking and planting the cutting/pup. This banana won’t fruit for another year or two, but the other 2 plants in our greenhouse should produce bananas from about June.



Banana pup

We grow Dwarf Cavendish bananas. This variety grows to 6 - 8 ft (1.8 - 2.4 m) and it is very fast growing. The bananas produced grow to 15 to 25 cm in length, and have a thin skin. Each plant typically produces 80 - 90 bananas when it fruits.

The bananas in our greenhouse are grown hydroponically (without soil). The planters use the Ebb & Flood technique which means water is pumped from a resrevoir below the planter to the plant roots several times per hour. Whatever the plant does not use drains (ebbs) away back into the resrevoir.

As the water ebbs away fresh oxygen is drawn down into the root area. This means that plants have great access to water, nutrients and oxygen. We think that the fact that we harvest on average 80 - 90 bananas a year is pretty good evidence of the effectiveness of this method of growing.