Rootrainers are a must-have for strong seedlings – they're ideal for sweet peas and beans

Rootrainers are absolute staples in a gardener’s sowing kit: they’re designed to promote healthy root growth and make things a lot easier when it comes to planting indoor-raised seedlings outdoors. What are rootrainers, though?

If you’re hoping to sow seeds successfully indoors and then smoothly move the young plants into the garden, rootrainers are a game-changer. In a nutshell, they’re a type of seed-starting container, and they’re especially useful for plants that grow long taproots, like sweet peas.

Here’s how rootrainers work, their benefits, and which plants are most fond of them.

What are rootrainers?

So, what are rootrainers? Above all else, they’re superheroes at encouraging strong root development – and that’s exactly what seedlings need for a healthy start in life.

‘Rootrainers are deep, narrow seed-starting containers designed to encourage strong, straight root growth by guiding roots downward and preventing them from circling,’ explains Lance Russell, brand sales lead at Thompson & Morgan.

This Oakland Gardens Rootrainer Set, £11.85 from Amazon, has 32 cells, so you can start lots of seeds at once.

I mentioned before that they’re a type of container that gardeners use to start seeds, but their design is what makes them really unique – and they’re much more interesting than a regular seed tray or pot.

‘Rootrainers are an alternative to traditional plant pots,’ says Kate Turner, gardening guru at Miracle-Gro. ‘They are longer, thinner pots that open up sideways and encourage roots to grow down rather than spiral round and round the pot.’

Think of them a bit like a book – that’s how they open, and that’s exactly what makes transplanting so much easier.

‘Their book-style opening allows seedlings to be removed with minimal disturbance, reducing transplant shock,’ says Lance.

I think rootrainers are really satisfying, because once you open them up, the individual cells reveal a neat little block of soil which contains the roots of each seedling. According to Kate, they’re a game-changer for plants that form long taproots, like sweet peas, peas and beans.

That’s not the only benefit of rootrainers, though – they’re also brilliant at keeping seedlings healthy from the base up.

‘The open base promotes air-pruning, which leads to a denser, healthier root system,’ explains Lance.

If you find that mould grows on the soil around your seedlings, rootrainers are good at keeping that at bay, too.

‘The design also helps prevent mould, as the bottom of each rootrainer cell is an opening, allowing for drainage and aeration,’ adds Kate.

Are there any drawbacks?

The only disadvantage of rootrainers is that you’ll need to water them more regularly. That’s good news for those of us who are prone to overwatering our plants – but it’s worth bearing in mind if you do sow seeds in rootrainers.

‘They do require more attentive watering as they dry out faster than standard pots,’ says Lance.

There’s also, of course, the cost to consider – but many models are on the affordable side (even these deep rootrainers from Crocus, which are £12.99 (or £11 each if you buy a set of two).

If you’re keen on upcycling ideas for the garden, there are other ways to grow long-rooted seedlings on a budget.

‘If you’re looking for a cheaper alternative, I tend to use toilet roll tubes for sowing my peas and beans as they also train the roots down and I can plant the whole thing in the ground,’ says Kate.

‘However, there is a higher chance of mould in this method, which rootrainers are well adjusted to stopping.’

Where to buy rootrainers

For strong root development, healthy root formation and minimal mould, rootrainers are absolutely worth the buy – especially for peas, beans and other taprooted seedlings.