Growing Tomatoes In Large Pots
There’s a great feeling of relief when planting tomato plants into their final growing position – a feeling that they’ve finally made it!
After months of special care, potting on and moving trays of seedlings from one position to another, it feels like the job is almost done. However, in some ways, it’s only just beginning!
Feeding, pruning and disease prevention will keep us fully occupied for the rest of the growing season!
Optimisation For Large Pots
The balance between moisture and air capacity.
A standard large pot or container can of course be divided into three levels of top middle and bottom.
Each layer should complement the needs of the plant’s roots.
Top Two Inches
The top layer is where most of the oxygen is absorbed by the surface roots.
It is also fairly dry because of moisture evaporation and water flows downwards.
This is the largest area of a pot where both moisture, air and nutrients are in balance with each other – hopefully!
Bottom Two Inches
Owing to compaction and excess moisture, when watered from below, the bottom two inches pose the biggest challenge.
- Potential water logging that creates bacteria which attacks the root system.
- Poor air capacity owing to compaction and saturation.
- Build up of nutrient salts that can be harmful to the roots and produce unwanted results in the plant and fruit.
In order to avoid some of the possible problems that can arise, here are a few tips on how to best optimise these three levels or pot areas.
The dry(ish) soil at the surface is good – it helps roots absorb oxygen.
Remove lower leaf branches and any dead leaves on the surface to keep a good air flow at the soil surface. This will help increase oxygen intake and help prevent disease.
When potting, remove bottom few branches and pot lower in the soil.
This area should contain a mix of compost and perlite or media that will hold moisture and air.
The moisture holding capacity of compost varies widely depending on what’s in it!
John Innes is a recipe that contains clay which holds moisture very well.
John Innes also contains sand and grit which adds air and drainage owing to the gaps between the sand and grit particles. It has the benefits of multi-pupose with perlite added!
One way of getting more air into the middle area of a large pot or container is by using an air pipe.
This is particularly good for getting air to the roots. One of the big disadvantages of using pots is their small surface area – compared to growing directly in the ground.
What Is An Air Pipe?
An air pipe is a plastic or rubber pipe that runs vertically from the surface to the bottom of a large pot.
An air pipe allows air down into the mid and lower levels of a pot and is added when the pot is filled with compost.
Holes are drilled in the side of the pipe to allow air into the root zone – from top to bottom. An old length of hose pipe or any plastic tubing will do – as long as there are plenty of small holes to allow oxygen into the roots and other gasses to escape!
As we know, a good oxygen supply to the roots means quicker, healthier growth and a bigger yield.
Soil Surface and Root Capping
One of the few disadvantages with growing tomatoes in large pots and containers is that the surface area is limited.
Roots take oxygen through the soil surface, so the less surface area there is, the less access to oxygen plants have.
This is especially relevant for a mature tomato plant that has been in a large pot for some time.
Fine roots circle at the soil surface creating a dense cap that prevents oxygen from entering into the root zone below. As we know, roots need plenty of oxygen for energy (respiration), without it, plants run out of steam.
One way to avoid root capping is to use air pots or fabric pots which allow air in through the sides. Of course the air pipe works very well too!
The Bottom Level
This is the danger area where harmful bacteria can breed and damage a plant’s roots.
If the container/pot is sitting in a tray, make sure that water is fully absorbed and not left for long periods.
A pot sat above a tray of water on blocks with a wick (as photo above) will access water/nutrients without the soil becoming saturated.
The use of capillary matting strips can help take moisture from the lowest level to the area above.
This is particularly helpful in soil with poor capillary action or when using high sided pots.
If using perlite, have the greatest amount at the bottom level where air is most needed.
A layer of clay pebbles at the surface and bottom of a pot helps for reasons stated above.
When can plants be left out overnight?
In the UK, it should be safe to plant outside from mid May onwards – the end of May in Scotland.
It’s good to “harden off” plants by getting them used to being outside where light levels are higher, the temperature range is greater and the breeze/wind plays a factor too.
That’s it for this week.
I hope all your plants are doing well!