How to repot houseplants – from what size pot to choose to whether you should remove all the old soil

Every plant lover (or even reluctant plant parent) knows that there comes a time when you have to figure out how to repot houseplants. The problem is knowing exactly what it is you should do.

At one time or another we've all simply dug our plants out, popped them in a bigger pot with more compost and hoped for the best. But garden experts suggest a few easy steps to ensure your indoor plants not only survive, but thrive, from the move.

How to repot houseplants

Before you get cracking with the do’s and do not’s of how to repot houseplants, you should first ensure you know when they need repotting. The time of the year places a crucial role, but the plants themselves will show signs that a repotting is due. ‘These include the plant noticeably outgrowing its pot with roots coming out the bottom and yellowing leaves,’ says Tom Cook, houseplant buyer at British Garden Centres. 

However, not all signs of an unhappy plant equal a need to get repotting. ‘Don’t repot stressed plants,’ warns Chris Bonnett, founder of GardeningExpress. ‘If your plant is looking distressed then try to avoid repotting until you can figure out why. You should only repot this if the soil turns out to be the issue.'

What size planter to repot in

It can seem a little Goldilocks-esque to try and select the right new pot for your fast growing plant, but it’s actually much more simple than you may have bargained for. 

Tom from British Garden Centres advises choosing a pot two inches larger than your current vessel, but you don’t have to be as precise as this if that’s not your style. ‘Choose a pot that is slightly larger than the current one to give the plant's roots enough room to grow,’ adds gardening expert Chris.

If your plant requires a root ball trim before repotting then Kelly Dyer, plant doctor and horticultural lead at Patch Plants explains that you should actually report into the same size pot as before.

How to move plants from one pot to another

While, yes, the physical process of how to repot a houseplant is more or less 'remove from old pot, put in new pot', there are a number of things you should be aware of, and ways to make sure your plant is sitting pretty in its new home.

'As you transfer your plant, always inspect the roots for any signs of diseases or rot even if the plant seems healthy,' advises Chris. Once you've given the roots the all clear, you can proceed.

'Gently lift your plant from its old pot, careful not to break off any stems,' says houseplant pro Tom. 'Massage and separate the roots before placing your plant in the centre of its new pot and fill with compost around its perimeter.'

Positioning correctly at this point is an important step. 'Position your plant in the centre of the pot so that you can backfill soil evenly around the root ball, and so that it looks good,' says Kelly.

Think about the level of the soil, too. 'Repot your plant to the same soil level that it was at before - you don’t want exposed roots,' Kelly explains. 'In most cases this will mean first putting a layer of soil at the bottom of your new pot to get the plant to sit at the right height.'

Should you remove old soil when repotting?

Ah, the age old question for any repotter – is the old soil meant to come with the plant, or should you just be replacing it with fresh material? The answer is somewhere in the middle in that you can bring a little bit of the old stuff, just not too much.

'Once you’ve taken the plant out of its existing pot, carefully break off the top ‘crust’ that has formed on the soil surface and gently ruffle up and loosen its roots (underneath and around the sides if possible) to get rid of any old excess soil,' explains Kelly. 'This will make it easier for the roots to start finding their way into the fresh soil. Even if some of the smaller roots break, that’s okay, this will stimulate new root growth.'

'If your plant seems to have stunted growth then it’s worth changing the soil,' adds Chris. 'If the plant seems to be growing okay you won’t need to remove all of the soil. Simply shake off the excess from the roots and add fresh potting mix around the root ball.'

As for what exactly the new soil will be may depend on the plant, but there are some varieties that make most happy, not just the hard to kill plants. 'Most house plants will be happy in a multi-purpose compost or indoor potting mix,' advises Tom. 'These mixes absorb moisture very well and resist compaction, and along with a regular fertiliser will allow your plants to thrive.'

'If you are growing cacti or succulents, they prefer coarse soil, so we recommend a specialist compost which contains a high proportion of sand and grit,' he continues. 'Orchids or Phalaenopsis need a free- draining compost, often made of bark chips, peat moss and perlite.'

Backfilling the repotted plant

Right, new soil is in the pot, the plant is in situ – this means it's time for backfilling. 'As you’re backfilling fresh soil around your plant, gently press down around the outside of the rootball,' says plant doctor Kelly. This ensures that it’s sturdy, but also that there is contact between the soil and roots.'

'Don’t pack the soil too tightly,' Chris warns. 'This can put too much pressure on roots, restricting their growth and ability to absorb water.'

Don't backfill all the way to the top of the pot, leave a bit of space. 'Leave a good 2cm gap between the soil level and the top of your pot so that there is room to water,' advises Kelly. 'If the plant is potted to the very brim of your pot, the water will run off before it has a chance to soak through.

'As you’re backfilling the pot, give it a few taps round the sides and on the table, so that any air pockets below the soil surface are filled,' she adds. 'If you find that your soil level drops down a lot as a result of this, top it up.'

Aftercare

So your plant's been repotted, what now? Well, you give your plant a good old, well-earned drink. 'Water the soil (not the leaves) until the water runs through the holes at the bottom of the pot,' advises Kelly. 'Let it drain and pop it back into its decorative pot.'

Bish, bash, bosh – you've got a beautifully (and healthily!) repotted plant.