For many gardeners, repotting and replanting are two important tasks for maintaining healthy, thriving plants. It’s also a part of the propagation process, helping introduce new and exciting varieties to gardens. But to maximize your gardening success, and the potential of your greenhouse plants, a key part is to understand the correct techniques and methods for repotting and replanting.
Greenhouses Direct have put together a handy Gardener’s Guide to repotting and replanting full of valuable tips and step-by-step instructions to help you confidently repot and replant your greenhouse plants.
The importance of repotting and replanting
Plants grown in containers will eventually run out of space to expand and grow. Also, as the plant grows and its roots take up space, the compost gets to the point where the plant can’t absorb as much water or nutrients.
This means that plant growth slows down, the root system gets restricted, and the compost’s organic materials start to break down, leaving little air space. If the roots become a knotted mass, water can’t drain properly and the plant becomes waterlogged, leading to potential root rot. All this means you could end up with a stunted plant that may even wither and die. Repotting allows you to give the plant more space and replace the compost to feed the plant in a larger container.
You may also have plants that have grown too big for the area they are in or need to have their tuber roots split to aid growth. Lifting the plants, splitting them and then replanting them gives all the plants more space to flourish.
When to repot and replant
The first thing to remember is that repotting and replanting impact the plants and can cause them stress. So, it’s advisable not to do it too often; every three to five years is ideal for most plants.
The best time to repot and replant is when the plant is at its strongest, i.e. during its active growing period. Spring is the best time for most varieties of grasses, shrubs and trees when it should give them a growth boost. Many plants respond well to repotting and replanting during early to mid-summer too. It’s better not to repot or replant in autumn or winter as the growing period is coming to an end, and the ground or compost in pots runs the risk of becoming too wet.
However, if you are repotting or replanting into pots in your greenhouse, it is possible during autumn and even winter if you can maintain the best environment for the plants.
Aim for spring to divide perennials that flower in the summer, but for those that flower in spring divide them during the previous summer. Herbaceous perennials can also be divided at this time, and the new separate plants replanted.
Choosing the right containers for repotting & replanting
A key aspect of repotting is ensuring you select the correct new container for the plants. It shouldn’t be more than a third bigger than the original pot, i.e. about two inches larger in diameter. Otherwise, you risk overpotting, potentially leaving the plant with a waterlogged compost and too many nutrients.
Also, make sure the new container is deep enough to allow the roots to grow and spread. If the diameter is two inches wider, but the depth is the same or less than the previous pot, you will still be restricting root growth as the roots won’t be able to expand downwards.
Make sure that the pot has sufficient drainage through a hole or holes in the bottom. You can add a thin layer of small stones/pebbles to aid drainage, then fill it with a good-quality compost or potting medium.
If you are repotting into big containers that when filled will be heavy to move, put them in their final location before you start to add compost and the plant. Choose a place where the plant will get the right level of sun and shade, and protection, depending on what suits the plant's needs to grow and thrive.
A step-by-step repotting process
Although the repotting process can be simple, care is needed to ensure the roots and the plant don’t get stressed or damaged. Here’s a step-by-step guide to repotting plants.
Step 1 – Before you start, make sure you have all the tools you need, the compost or potting medium, and the new pot ready and to hand. Avoid watering the plant before repotting, as dry compost is easier to remove from the pot.
Step 2 – Gently hold onto the sturdy stems at the bottom of the plant and carefully lift them from the old container by pulling them up and out. You will probably need to hold the container down at the same time. If it doesn’t slide out easily, put the pot on its side and see if the plant will pull out sideways. Alternatively, and with someone’s help, hold the plant and turn the pot upside down, then try to lift the pot off the plant. If it’s really stubborn, get a trowel (or spade if the pot is big enough) and ease it down the inside of the pot around the compost to release it.
Step 3 – Once the plant is free of the pot, see how congested the root system is before repotting. If the roots have spiraled around at the bottom of the compost or out to the sides, gently tease them out until they are straighter, then trim a little. If you’re repotting to refresh the compost and replace it with new, take about a quarter of the outside roots off the plant before repotting.
Step 4 – Take the new pot and make sure there’s a drainage hole; you could also add a layer of stones to help aeration. Next, add a layer of compost or potting medium to the bottom of the container and press it down firmly. Place the plant into the container so that it sits just under the rim of the pot. Then add the rest of the compost to the pot, down the sides of the plant and a layer on top, pressing firmly down to get rid of any potential air pockets. If you have some roots poking through at the top, lightly cover them.
Step 5 – Once you’ve filled it with compost, take a hose or watering can with a fine spray attachment or rose attachment and water the plant. The first time you water the plant, make sure you thoroughly soak the compost. A good indicator is watering until it comes out through the drainage hole.
A step-by-step replanting process
The replanting process is very similar to the repotting process, but you are managing bigger plants and have to split root clumps and tubers. Again, be careful to protect the plant as much as possible. Here’s our step-by-step guide to replanting.
Step 1 – Get your tools together and the replanting hole dug out, adding a little fertilizer and replanting compost in the bottom to encourage growth early on before you start. It’s better not to water before replanting as the roots/tubers will split more easily in dryer soil. Choose the position carefully according to the plant’s needs.
Step 2 – With a garden fork or spade, gently dig out the parent plant from the ground. Don’t dig too close to the roots to avoid damaging them as much as possible. Once the plant has become loose, gently lift it from the soil and place it on one side. Refresh the hole with fertilizer and replanting compost to get it ready to put the parent plant back in it.
Step 3 – Lay the plant on its side and, with a spade, fork or by hand – with some plants that have multiple tubers, it can be easier to break them apart – carefully split the root clump into two or more, keeping as much of the top growth as you can, so that you have one or more new plants.
Step 4 – Place the parent plant back into its original, refreshed hole and fill the sides with soil or a soil/compost mix. Press down firmly until the plant is secure and add a layer of fresh soil/compost on top around the base of the exposed plant. Repeat this with the new plant(s) in their respective new hole(s).
Step 5 – With a hose with a fine spray attachment or a watering can with a rose, water the parent and new plants thoroughly to help the plants get a good start. Don’t be surprised if they take a while to recover and you see a growth spurt, as replanting can delay growth – be patient.
Repotting and replanting aftercare
Once you’ve repotted or replanted, clean all your tools and brush off any excess compost from the pots with a damp cloth or soft paintbrush. For repotted succulents or cacti, you probably won’t need to water again for at least a week to allow their roots to settle and establish themselves.
You may find some plants take a while to flourish and grow again. This is because the process can cause them stress, and it takes time for them to get used to the new compost. So, be patient and give them time.
Avoid over-watering by checking how dry the compost is before you water them, and be careful not to overwater. Don’t leave them standing in water, either. If the plants or compost hasn’t absorbed excess water, throw it away.