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 maximise 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.
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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 o