So it's time to repot the chili plants to larger containers! Please read our previous articles about pot and soil selection to get the basics first. You have the pot and the soil, so let's get started! Please note that for perennials the best time to repot a plant is in the spring so that actively growing roots will have enough time to grow into newly added potting mix.
The steps for repotting are simple:
Make sure the soil of the plant in its original container is moist. If not, water the plant.
If the new pot was used previously make sure that it is clean before you start.
Turn the pot and the plant on their side. Remove the plant from the old container. A dull knife can be handy tool to tease the soil and roots apart from the old pot's edges.
Gently rub the roots and the old soil on the soil ball. Remove the loose old soil that drops out easily.
If roots are circling the rootball loosen them or remove some of them until roots are hanging down. Avoid removing more than 1/3 of the roots.
If you're using a pot with a large drainage hole you can cover the hole with a dense net or a piece of broken claypot to prevent soil from draining out. Don't put anything else at the bottom.
Put potting mix in the new container. Make a groove for the rootball so that its top is below the lip of the new pot.
Add more potting mix around the rootball and gently firm the top soil until it fills the container. Don't compact too much. Watering will compact the soil later!
Water the new soil and place the plant in its new location.
The bottom of the container
Do not put gravel of any other kind of coarse material at the bottom of the pot. There's a common myth circulating in the gardening communities that one should put something at the bottom to increase drainage. This is incorrect! The coarse material will not hold water, and therefore the most damp soil at the bottom will be located upwards towards the roots. This mechanism of action works by osmosis and is well studied and documented.
Please refer to the picture below from The Garden Professors facebook discussion. See how the layer of wet soil is raised upward when there is gravel at the bottom. This exposes the plants to root rot.
Source: The Garden Professors blog facebook group.
Removing the plant from old container
First water the old soil, preferably one hour before the repotting. This makes the soil soft and helps removing the plant from the pot.
Picture below shows a neat trick to help loosen the plant's roots and the soil from the edges of the pot. Sometimes they hold on to the pot and you need to help loosen the edges a bit with a standard dining knife.
Pulling the plant out might be easier if you tilt it on its side first, and pull gently.
Removing loose soil and loosening roots
If the old soil is well moisturised it will fall off easily when you gently rub it. The soil in the picture below literally fell off after rubbing it lightly on the edges. Gentle shaking will help to remove some of the loose soil.
Spread some newspaper on the floor to make the soil change a less messy job.
Root-bound or pot-bound?
These terms mean that plant has outgrown its container and the roots have started to circulate inside the pot's edges. Basically what happens is that when watering the pot's inner side will get wet and the roots are trying to capture the moisture from the edges. This is a problem when you repot the plant and expect it to grow roots into the new soil. If the rootball looks like a thick forest of roots shaped like a pot you can be sure this will be a problem. Another sign of root-bound is when you notice roots growing out from the potholes. Root-bound plants will not be able to grow new roots efficiently outside of their rootball shape. Therefore they are said to be "bound".
If you notice roots growing out from pothole it's time to repot!
If you have a root-bound plant you need to revise your goals. Do you intend to keep the plant in its current size or do you want it to grow larger? If you want to keep it small (making a bonsai chili (bonchi), for example) then remove the outer section of plant roots, return the rootball to the container with some new potting mix, and cut back some of the plant's top growth. If the goal is to let the plant grow larger, get ready to repot it.
Picture below shows a chili plant's rootball that was rootbound. It was earlier repotted but the plant was unable to grow roots to the new medium. The new (dark) soil fell off the bottom and had no new roots in it. Some roots were removed from the edges along with soil, and the plant was repotted to a larger container.
Don't remove more than 1/3 of the roots. Removing too much can slow down growth.
Sources:
https://extension.psu.edu/repotting-houseplants
Top up soil and place rootball in
Below picture shows the new container filled with a mix of vegetable potting mix and compost. The plant's rootball is placed below the level of the edges of the container.
Tip: When using grow bags lift up the bag and thump it a few times against the floor to let the soil settle in. The bag is flexible and expands.
Remember to water the soil well after repotting!
Repotting plants from hydroponics to soil
Sometimes you may want to repot plants from hydroponic growing medium to soil. The only remarkable difference is that plants may grow different shape and size roots in hydro compared to soil. And of course, you won't have remove the old soil or be so much concerned about root-bound problems.
The picture below shows a thai chili padi variant (bullet chili) that was grown in hydro. It has grown remarkably small roots. The growing medium was rockwool placed within a plastic harness to support the plant. The plastic support was removed with scissors. Rockwool is an inert (neutral) growing medium that retains a lot of moisture and allows nutrients to pass through. There is no need to remove rockwool when planting to soil in this case.
Even in this extreme example the plant was happy after being repotted to a small balcony railing pot. If the roots are small place the plant in shade and allow it to grow larger roots first.
From mid-size pot to large pot
When you're doing repotting it's good to use right size pots. After the initial germination to seedling you're usually good with a small-to-medium size pot. The picture below shows a 5 litre container with a happy mid-size Carolina Reaper plant. Soon it was time to repot it to a larger container.
Happy repotting moments!
-Chilious