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  • Container plants or potted plants are an excellent way to add some colour and interest to your garden. Containers can be moved about, changed relatively quickly and allow for your garden to evolve each year. There comes a time when all container plants will require repotting. This is a beginner's guide to showing you exactly how this can be done to ensure beautiful plants!

    Overtime container gardens or pot grown plants will need repotting to ensure further healthy growth and flowering. As gardeners, we may use containers to propagate plants from seeds or cuttings. We may also choose to use pots to allow us to move plants around the garden in and out of season.

    Potted plants can also be useful in container gardens where there is no soil. Balconies, urban spaces and city gardens may all use containers or potted plants to bring some greenery to otherwise hard spaces.

    Beginner Guide to Container Gardening

    Why use container plants?

    Container planting allows you to plant literally anywhere and in any sized garden. There is no need to have soil or earth to plant into. It allows you to plant in containers usually using a growing media such as compost and bring plants and arrangements to otherwise garden-free spaces!

    A container garden on steps

    Container gardening enables you to also move around plants to create multi-layered schemes. It also means that season planting can be moved out of view once the plants have gone over for that year.

    Designers sometimes use containers to enable planting where otherwise there would not be any and to break up hard landscaping.

    What is repotting of plants?

    Repotting is the simple act of lifting a plant out of a pot, checking the roots and repotting. Sometimes repotting into a larger container but always replacing the growing medium or compost during the process.

    Garden Ninja carrying a crate of plants

    Why do we need to repot plants?

    You may be wondering why we don’t just leave containers or pot grown plants alone as they are. However, they do require some maintenance to ensure they give us the best display. We repot plants for a number of key plant health reasons:

    1. Root bound plants stagnate in containers

    After a few seasons or years, any container plant will eventually become root-bound or root balled. This is where the roots of the plants reach the edges of the pots and carry on searching for water and nutrients by then growing back around the pot. If left unchecked the plant’s vigour may suffer.

    a root boun dpotted plant

    A root-bound plant has outgrown its container and either needs the roots trimming back to encourage more growth or they need to be repotted into a larger container.

    2. Encouraging new growth from container plants

    Repotting on into a larger pot can also enable new growth and vigour to the plant essential to keep it giving you seasonal displays of interest. This is because the larger pot encourages further root growth and means the plant can grow more vigorously.

    Whilst plants will have an ultimate height and spread, the size of the container they are grown in does influence them. Just think about bonsai trees for example!

    A collection of Bonsai trees in Hong Kong

    To replace the growing medium or compost

    Container plants can’t locate nutrients or water from anywhere but the pot that they grow in. Meaning they are completely reliant on you for water and feed. Plants that are in the ground can access soil and send out roots far wider than in containers. Meaning that a container garden does require more careful maintenance.

    After time the growing media in containers may simply break down to nothing more than dust. To keep the plant healthy it is wise to replenish with compost or other organic matter to keep your plant in tip-top shape.

    A row of container plants

    This also keeps the soil structure in the best possible form, meaning it can free drain, yet retain the right moisture content, neither too wet nor too dry!

    Equipment needed to repot

    1. New pot ideally larger if space permits
    2. A garden trowel
    3. Replacement growing media – compost, soil, perlite a mixture of the three.
    4. Compost scoop which is larger than the trowel
    5. Gardening gloves – save your precious hands
    6. Kneeling matt – to save your knees!
    7. Mulch for the top of the pot whether it is decorative or organic
    Tools for repotting a plant

    How to repot a plant

    Repotting a plant is super easy and by following this guide you can make sure that your container plants thrive producing an abundance of flowers, fruits or vegetables each year.

    Step 1. Clean your new pot

    Firstly you will need to make sure that the new pot is sterile, clean and free from debris. Always make sure that your tools and equipment are as clean as possible.

    If not you risk spreading disease and pests to your lovely plant. The kneeling pad and gloves are to protect both your knees and your hands, essential if you’re a keen gardener to save thorns, debris, and filthy nail syndrome!

    cleaning the new pot

    Step 2. Ensure there is sufficient drainage

    Drainage is essential for container gardens. If not the plants can literally drown. Most plant pots and containers come with a series of drainage holes at the bottom. Sometimes there are lots of small holes or one large central drainage hole. A good idea for larger pots is to insert what we gardeners refer to as crocks in the bottom of any plant pot.

    Crocks for pots are broken bits of old clean pots, stones, or chippings used to add a barrier between the bottom of the pot and the growing media ie compost.

    crocks in the bottom of a pot

    Why do we do this? This is because the holes are usually rather large in big pots and without the crocks the pots can free drain too quickly, meaning the plants will dry out. Crocks in all pots can help the bottom of the plant sitting in water which can lead to root rot.

    Also, the growing media can sometimes leak out causing the soil to be lost and staining the surface underneath the pot.

    Step 3. Lift your plant out of the existing container

    The next step is to carefully lift the existing plant out of its current pot. Take care so you don’t damage the plant or its root system by forcing it out. Sometimes tapping the side of the pot can help loosen it or work a trowel around the edges.

    Root bound plant in container

    If a plant is really root bound sometimes breaking the plastic pot or cutting it open is easier.

    Step 4. Check the plants root structure

    Inspect the root structure of the plant when you have removed it. Does it look congested? If so you can tease the roots apart to help loosen them. Sometimes it is actually worthwhile using a sharp knife or scissors to cut away sections of the root ball to free them up.

    A root bound young plant

    This also spurs the plant onto product more healthy roots once repotted. Just take caution not to be too scissor friendly! Only removing up to 1/5th of the current root structure anymore and the existing plant may struggle to sustain itself.

    Step 5. Choose a growing media to repot the plant into.

    I always use peat-free compost or even better homemade compost. Peat free is super important as peat is a non-renewable growing media. This means once it’s dug up it takes thousands of years to replenish, and whilst it’s high in nutrients there are far more sustainable alternatives.

    Ensure there is enough compost in the bottom of the new pot so the plant when placed inside comes up to just below the new pot rim. Too high and water will run off rather than penetrate the soil making it very difficult to water!

    backfilling the new pot

    Step 6. Backfill around the plant with the fresh compost

    It’s now time to backfill with new compost. Ensure you firm it down to ensure the plant is stable, level and in the right position. Once you are happy with this you can then add a decorative mulch to the top of the pot as a final step.

    Step 7. Mulch the top of your container plant

    A mulch can help retain water in times of high temperatures and also stops the top surface of the soil from eroding. It also can really finish off a potted plant giving it that design flair! The mulch could be some chipped bark, pebbles, gravel or even leaf mould.

    I’ve used white pebbles, bought from an approved source, you must never take rocks or gravel from the wild as this is both illegal and damaging to environments.

    pebbles as mulch

    Step 8. Water your newly planted container

    The final step is to give the plant a good watering, ideally from rainwater caught in a rain butt or other environmentally friendly source. Rainwater, usually, has a more balanced PH and doesn’t contain fluoride and other chemicals that our drinking water must contain.

    It’s also more cost-effective to reuse ‘clean’ water where possible. Then you’re done! A newly repotted plant to continue giving you many seasons of interest!

    watering in a new plant

    Why you shouldn’t use soil in container gardens?

    This is a commonly asked question about why as gardeners we don’t use soil from the garden in pots and containers.

    The reasons we don’t use soil in container gardens are:

    1. Soil is incredibly heavy when wet making moving pots difficult
    2. Compost has a higher nutrient content and retains moisture more effectively
    3. Soil is a living organism and in containers over years the complex bacterial relationships can die off vs soil in the ground that can replenish itself
    Garden Ninja digging a trench for a hedge

    When potting on a plant a good rule of thumb is to try and mirror the conditions that the plant likes in the wild. So if planting an alpine plant that needs free-draining soil you may need a 50/50 mix of compost and grit or perlite. Plants that need damper rich conditions may need a mix of compost and manure for example.

    Plant Pot Size Guide

    Below is a guide to the UK plant pot sizes. Usually listed in litre sizes. It can be confusing as a new gardener to know the difference between a 9cm or P9 pot and a 2 litre. The chart below shows you the standard pot or container sizes including their dimensions.

    Pot SizePot Diameter at the topPot Diameter at the basePot Height
    9cm (P9)9.0cm6.0cm8.5cm
    1 Litre (C1)13.0cm10.0cm11.0cm
    2 Litre17.0cm12cm13.0cm
    3 Litre19.0cm13cm15.0cm
    4 Litre20.0cm15.5cm16.5cm
    5 Litre22.5cm16.5cm18.0cm
    7 Litre25.0cm19.0cm20.0cm
    10 Litre28.0cm24.0cm22.5cm
    15 Litre33.0cm25.5cm30.0cm
    20 Litre35.5cm27.5cm32.5cm
    25 Litre38.5 cm30.0cm35.0cm
    30 Litre41.0cm33.0cm36.0cm
    40 Litre50.0cm35.5cm45.0cm

    Sometimes C or P is used before the litre or size further to confuse things. It’s really the number you’re looking at. Anything with a 9 is usually the smallest plant pot size used to propagate plants. When you get to the 10 litres and above in pot size, you’re looking at larger established plants and shrubs. So the cost of these sizes will vary according to the age and maturity of the plant.

    Below we have P9 the small square pots, then circular 1-litre pots and larger 2-litre circular pots. The green rectangular stacked pots are 3 litres for reference.

    A group of plastic plant pots in a garage

    If you haven’t already read my guide on why plastic pots should be avoided where possible due to the lack of recycling facilites then you can read that here!

    Summary

    Potting on container plants each year or two is a surefire way to keep your garden looking fantastic each year. By choosing the correct peat-free growing medium and also trimming back roots your planting opportunities will know no bounds!

    Even if you have a tiny rented garden or balcony container gardening can help you make the most out of your space. So what’s stopping you from container gardening?

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    Happy gardening!

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    2 thoughts on “How to repot a plant: container gardening top tips

    1. Billy says:

      Hi, thanks for this. I want to repot my hydrangea when is the best time for this please?

      1. lee says:

        Hi Billy, Early spring is the best time. Once the frosts have passed. They like an ericaceous compost and growing media. Happy Gardening! Lee

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