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Made In Britain Homegrown Company
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Root Trainers - What Are Root Trainers Good For?

Root Trainers - What Are Root Trainers Good For?

11 minute read

Root Trainers (sometimes referred to as rootrainers) were originally produced by a small vaccuum forming company in the Scottish Borders called Ronaash. Reported as new technology in NewScientist in July 1989 as ‘A Scottish company is making a new kind of plant pot that could revolutionise commercial forestry and horticulture. The new pots, called Rootrainers, help to produce a plant that is better able to survive the shock of transplantation.”

These revolutionary pots were originally moulded plastic sheets that were shaped to form ‘pots’ in a line, with a ‘fold’ or ‘hinge’ along the base. They were supported a few centimetres above the surface of the ground or bench using a special frame which the lines of ‘pots’ slotted into.

root trainers by Ronaash

How Do Root Trainers Encourage Strong, Healthy Root Structure?

As the photograph of the rootrainer shows, each ‘pot’ had a large drainage hole at the base and a series of parallel grooves running down the sides. It was this combination which resulted in ‘air pruning’ taking place when the plants roots started to emerge through the drainage hole at the base of the ‘pot’. As the roots emerged into the air the roots would dry out and so called ‘air pruning’ would kill the growing tip of the root.

air pruning in root trainers

In response to this pruning, the plant would automatically produce more roots. And as more roots were produced they would tend to grow towards the sides of the rootrainer. Once the roots reached the sides the deep grooves would force the roots to grow down to the drainage hole where the new roots would emerge and more ‘air pruning’ occur.

In this way you encourage your plants to form a very strong, healthy root structure.

How Do Root Trainers Prevent Root Damage when It's Time To Transplant? 

As each plant has it’s own space to grow in, the roots do not become entangled with their neighbours, so when it comes time to transplant they are easy to handle without root damage.

When it’s time to plant out the seedling, the moulded and folded plastic sheet can be opened – similar to a book – to release the seedling. There is no need to use a dibber or widger to loosen the roots – plus the plants straight root system will point straight down and when planted into its new location will continue to grow straight down into the soil and anchor the plant firmly. As the plant roots aren’t disturbed, the plant will continue to grow quickly in its new home.

Which Plants Are Best Grown In Root Trainers?

Rootrainers were originally invented by Henry Spencer, a Canadian, who was thinking about foresters in North America needing a way to airlift large quantities of seedlings to remote places so they could plant new trees to replace the ones they had felled. Rootrainers compact shape made transportation easier. 

Developed for foresters, they were soon used for growing other plants as explained by Robin Currie, managing director of Banff and Buchan Nurseries, where they began to experiment with growing ornamental shrubs in root trainers

“Because the roots aren’t damaged, they grow much better when we line the cuttings out in the field”

Soon amateur gardeners quickly became interested in using rootrainers for plants that don’t like to be transplanted, including sweet peas and sweet corn.  

As rootrainers have become popular they are now used for growing all kinds of vegetables and flowers, although they are most beneficial when they are used to grow large seeds which naturally have deep root systems, including all types of peas, beans, peppers, fennel as well as delphiniums, sweet williams, sunflowers, sweet peas, wall flowers and virtually all types of trees.

which plants are best grown in root trainers

How Deep Are Root Trainers? 

    Due to the popularity of rootrainers their orginal design has been developed so that it now available in four different sizes:  

    how deep are rootrainers

    Maxi Root Trainers – these are the largest modular rootrainers which you will find on the domestic market and features 8” deep rootrainers that fit into a holding tray 11” x 17½”. These root trainers have been designed to accommodate broad leaf trees grown on a long cycle to larger saleable sizes and for plants destined for dry sites.

    We don’t stock this size of root trainer as they are more specialist than the Deep or Rapid Root Trainers which are used by the majority of amateur gardeners.

    Deep Root Trainers – combining a good growing depth of 5” together with a compact holding tray 8½” x 9½” which holds sufficient root trainer ‘books’ to form 32 individual growing cells for your plants, you can grow a large number of plants in a small space. At the same time there will be no tangled root balls or pot bound plants, simply plants with a strong, straight, healthy root formation.

    Plants which are ideal to grow in these 5” deep rootrainers are beetroot, broad beans, french beans, runner beans, delphiniums, sweet peas, sweet williams, wallflowers etc.

    Rapid Root Trainers – these 3” deep rootrainers are supplied as a pack of 8 ‘books’, with each book forming 4 root trainers when folded.

    These fit neatly into a 14” x 8½” holding tray and can be purchased with or without a clear propagating lid. 

    Click here to see full details.

    rapid root trainers

    The size of the Rapid Rootrainers are ideal for raising bedding plants, such as snap dragons, begonias, lobelia, softwood cuttings from chrysanthemums, gernaiums, fuchsias, heathers, as well as small herbs like basil or chives or salad plants including tomatoes, radish and lettuce.

    Compact Root Trainers – ideal for gardeners with limited space, these root trainers are designed around a 8½” x 9½” holding tray which features slots to hold the root trainer ‘books’ securely in place. Unlike the tradtional Deep Root Trainers and Rapid Root Trainers, this compact version has only 20 cells rather than 32, each cell being approx. 3” deep and supplied as five ‘books’ to fill the holding tray.

    The manufacturers of these Compact Root Trainers recommends using them for growing salad crops, herbs, bedding plants, plug plants and cuttings.  

    How Do You Fill Root Trainers? 

    Due to the depth of the root trainers, filling them with compost can be time consuming. However, by researching how they are used with other gardeners, we have found that the best way to carry out filling your root trainers is as follows:

    • First put the rootrainers together – so the ‘books’ are folded and fitted into their holding tray.
    • Now place the holding tray into a larger tray – so a Potting Tidy or Potting Tray would be ideal as these are shaped to help prevent compost spillage – or any large tray which will catch any overspill of compost.
    • It’s now time to add the compost – the best way is to fill a tray with compost – large enough to cover the surface of the rootrainers – and invert this over the root trainers so the compost falls in. Or fill a pot with compost and sprinkle this over the surface of the root trainers.
    • To get the compost to settle into all parts of the rootrainers – lift the holding tray 4” – 6” off the tray and drop a couple of times to get the compost to move down. Then repeat the process until there is sufficient compost in the cells to sow your seeds.  

    sieving compost to remove lumps

    When filling your rootrainers choose either a multi-purpose compost or a seed and cuttings compost.

    Whichever you select, we always recommend sieving the compost before use as this ensures there are no lumps which could get in the way of straight root growth.  

    Click here to see details of a sieve.


    Can Root Trainers Be Reused? 

    One of the reasons that root trainers are so popular – their manufacturers state they have sold over 60 million cells in the last 20 years – is that they are economical.

    • Their shape – tall and thin – means less compost is used than if you were filling pots of a similar depth.
    • They have also been shown to have a long life – depending on their usage and the care you take – professional nurseries are getting six or more years use from these modular trays.

    rootrainers are modular systems

    • You can replace just the parts which wear out – being a modular system, you might find that you just need to replace some of the ‘books’, whilst the holding tray is still in perfect condition. At Two Wests we are happy to supply you with just the parts you need to replace – simply give us a call on 01246 451077 for a price.  

    The part of the root trainers which gets most use is the ‘books’.

    Hinged at the base and opening like a ‘book’ when it is time to transplant your young plants, constant opening to check on root growth and season after season of growing can make the hinge section vulnerable.

    Being able to buy just these books means you can continue to use the holding tray and makes rootrainers even more economical.  

    root trainer books

    How Do I Water Plants Growing In Root Trainers? 

    Due to the design of the rootrainer books ensuring your plants remain well watered might seem tricky – the root trainers are suspended off the surface of your shelving or benching in their holding tray so you can’t water using water matting or capillary matting. Also, the water will evaporate through both the hole at the base of each root trainer and from the surface.

    You could water with a mist system from above, but the simplest method most gardeners use is to make dual use of the optional clear lid which is available for rootrainers.  

    watering plants in root trainers

    The lid is large enough for the holding tray to fit inside – so simply invert the lid and half fill with water. Then leave the holding tray with root trainers in place for about 5 minutes. Watering complete!

    Can Root Trainers Be Used In A Propagator? On Greenhouse Benches? On Shelves? 

    Rootrainers can be purchased with an optional clear cover which turns them into an unheated propagator and for some plants will be sufficient to lift the temperature for seed germination.

    However, if you need higher temperatures for the seeds you have chosen to germinate, then you will need to use a heated tray, warming mat or heated propagator to give the increase in temperature that you require. Rootrainers are perfectly suitable for use on a heated surface or within a propagator – as long as the propagator is tall enough to accommodate the height of the root trainers and seedlings, such as a Vitopod.

    The holding tray which the rootrainer books fit into is ideal for standing on benching or shelving in your greenhouse – with their compact size enabling you to pack lots of plants into a small space.

    Unlike pots or trays which usually sit flush to the surface of your benching, the holding tray holds the rootrainer books slightly off the surface of the benching so that air pruning can occur. This just means you need to be aware of their watering requirements (as described above), but other than this they will work perfectly on the benching in your greenhouse.  

    rootrainer rack

    However, if you want to make the best use of your growing space and still allow air pruning to occur, then a specially designed Rootrainer Rack will do this for you.

    Our rack is available with 1, 2 or 3 levels, with each level securely holding four sets of rootrainers. This enables you to keep as many cells as possible in a small and organised space.

    Click here for full details.

    Our blog posts are created from our personal knowledge, information gathered by speaking to other gardeners or manufacturers in the gardening industry, by reading gardening magazines and devouring information from books and the internet. We aim to be as accurate as we can, so if you find a mistake, please remember, we’re only human. if you have any queries you can contact us today!

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