Container Size for Tomatoes
One question I’m regularly asked is “what pot size should I use?” for planting tomatoes in their final position that is.
The answer depends on a number of things including plant size, fruit size, leaf size, early or late to mature etc.
For example, a dwarf variety can grow in a 6 inch pot but most beefsteak varieties will need a much larger area for their roots.
A variety with a large leaf area will require a bigger pot (in theory) because it will lose more moisture through its leaves and therefore require a larger soil area from which to draw water.
Also, a variety that matures early may need less growing room because its season is shorter than a late maturing variety for example, so it needs less resources.
As valid, and long winded, as these points may be, they don’t get to the heart of the matter.
Better growing methods mean you can use smaller pots
The fact is, the better the growing methods used (i.e. growing media, type of container and access to water and nutrients), the smaller the container size that is required for a successful crop.
The plant below is Sweet Aperitif growing in an 8.5 litre pot using the Auto Pot system. It was trained to three stems.
For example, a tomato grower who uses the least expensive compost, a basic pot, waters and feeds inconsistently will need a bigger pot to achieve good results than someone who understands what their plants need and delivers it to them. The extra soil in a larger pot acts as a buffer zone or safety net!
With best growing practices, it’s possible to use a 10 litre rather than a 15 litre pot. It’s possible to grow most varieties successfully in a 6 litre pot too. It’s how we grow them that determines the pot size.
Containers vs Garden Border Soil
The above applies to container growing. If planting directly into the garden soil, the bigger the root system, the better.
If growing in containers, there is a limit to the size the roots can grow before they become pot-bound.
The idea in container growing is to give a plant all it needs so its roots won’t become too large and pot bound.
It is the case that a plant that receives water and food 24/7 – that’s whenever it needs them, will grow a smaller root system and be happier in a smaller pot.
Disadvantages of large pots
Bigger pots are more expensive to buy, take up more room and need more potting compost. Two important considerations for most of us are expense and space, not to mention carrying the heavy bags of potting compost!
Of course the question now is: “what do tomato plants need?”
Creating the best growing conditions
They need a good medium that contains lots of oxygen and doesn’t dry out too quickly allowing good respiration (see below) and avoiding water stress (see hormones below).
They need access to water and nutrients 24/7 – when they want them, rather than when we give them – leading to consistent transpiration and osmosis (coming soon).
They need good aeration when in a greenhouse, tunnel or on the windowsill producing good transpiration and avoiding disease.
They need plenty of light to maximize photosynthesis.
Lots more on these subjects in coming newsletters.
Here’s a link to a very useful page if you are interested in some of the more technical aspects that make plants grow, click here.
Blowing in the wind
Every morning I blow gently on my seedlings!
This may seem a strange thing to do, but there are at least four good reasons why it helps growth.
- Increases air flow in the window and helps get rid of any morning condensation.
- The aeration increases transpiration (moisture loss from leaves) and gets the circulation going.
- It provides extra carbon dioxide for photosynthesis – we exhale carbon dioxide.
- The movement encourages stronger stems.
It’s long been suggested that talking or singing to plants encourages growth – the truth is, that plants grow better when subject to carbon dioxide. We inhale oxygen (for respiration) and breath out carbon dioxide – good for us and plants!
Respiration and Tomato Plants
It is useful to understand respiration because by creating the right conditions, plants grow faster, produce more tomatoes and are healthier.
So what is respiration?
It is a process that happens when plants combine the sugars they make during photosynthesis, with the oxygen they mainly absorb through their roots.
In other words, respiration is the process of combining sugars and oxygen to create energy for growth.
So what can we do to optimize respiration in our tomato plants – or least make sure we don’t hinder it!
The most important thing is to provide plenty of oxygen for plant roots. This can be achieved by using perlite, vermiculite, air and fabric pots etc.
Respiration plays an important role in organics too. A well aerated rich soil will encourage friendly bacteria, and they need oxygen to play their role just as much as the tomato plants do!
There’s always a trade-off between moisture and air in the root zone. Too much of one leads to a reduction of the other – the challenge is to maintain a regular supply of both.