My seed sowing finger is getting “awful itchy” … Just four weeks to go until the middle of March – my seed sowing date!

Pot Sizes & Sowing Tomato Seed Early
The earlier you sow, the longer it is before you can plant out in the final position.

Plants need potting on to avoid becoming root-bound and running out of steam. As pot sizes grow, space for plants becomes tighter and tighter.

In the old days … just last season actually! I used to force-on tomato plants by using a number of pot sizes. Each pot that was used, a little bigger each time, would soon become too small for their roots.

I would use three or four pot sizes before final position … it was a lot of work potting-on and the penalty for sowing too early – too much time between sowing and planting out!

This potting method does encourages them to “get a move on” as their roots reach the sides of a pot and the plant thinks it has limited time, so it grows faster.

If you sow a seed into a large pot, it will take longer to reach the fruiting stage.

However, using a number of pot sizes is time consuming and there is a better way to growing strong healthy plants at a speedy growth rate.

Sow a little later and grow a little faster using perlite.

It’s In The Roots
Learning more about the roots of tomato plants and nutrient take-up, has made a big impression on the way I’m growing tomatoes this season.

I’ve always used perlite and vermiculite … a handful here and a handful there, but this season it’s more than just a handful!

It doesn’t matter if you are using the most expensive seed compost with added everything … the bottom line is … YOU NEED TO ADD MORE PERLITE … excuse me for shouting but I can’t over-estimate the importance of this, and I get a bit over-excited!

By using up to 50% of perlite I’ll be able to keep plants in their same pot size for longer because the extra oxygen in the root zone will help keep the roots healthy.

Option One – Earlier Sowing

  • That means I can transplant to 7cm pots
  • Then to 11cm pots
  • Then final position

Option Two – Later Sowing

If sowing in individual cells, plugs or sponges, you could transplant to 9cm pots then final position.
Either way, the roots will stay healthier longer and will take longer to become pot-bound.

Here are a few reasons why without perlite, your plants may suffer:

  • Absorption of nutrients is less efficient in potting compost alone because the roots of tomato plants need more oxygen than ordinary soil/compost can provide.
  • It’s easy to over-water and saturate potting compost which damages roots.
  • Compost in containers and grow bags also dries-out quickly, and when it does, water and nutrients are unavailable causing all sorts of problems including stress, and when plants are fruiting, Blossom End Rot.

Adding perlite gives a much better water to oxygen ratio and plants will be healthier and grow faster.

A mix of 50% perlite added to any multi-purpose potting compost will give the best results every time.

Deal of the week …

Perlite for tomato pots

Perlite at Wilkinsons is £3.75 for 10ltrs, B&Q it’s £4.98 for the same amount. Most garden centres sell it for more than that!

For seedlings and young plants, vermiculite is also excellent!



Nitrogen & Feeding Tomato Plants in Cool Conditions

We all know that plants need nitrogen to grow.

If more nitrogen is given to a plant than it can use, it will become soft and leggy and flowers may fail to set.

If too little nitrogen is available, plants become stunted and main stems become dark in colour and hard. Getting the balance right is often a process of observation.

Nitrogen comes in two flavours for our plants …

  1. Nitrate
  2. Ammonium

Too much ammonium will damage plant cells.

Temperatures and Nitrifying Bacteria
In warm growing conditions, soil bacteria and other microbes convert excess ammonium into nitrate. However, in the spring when soil temperatures are cold (below 10C), the job of “nitrifying”, turning ammonium into nitrate, is slower and ammonium builds-up to a level that can cause damage.

Here is a photo showing ammonium toxicity where the damage to the leaves is clearly visible.

AmmoniumToxicity on Tomato Leaf

I get a few of these marks every season on my plants and used to think that some little critter was the cause!

However the small marks are damaged cells from ammonium toxicity and very common.

Ammonium toxicity can also be displayed by leaves curling and lighter areas between the leaf veins.

One way to reduce the ammonium content or amount of nutrients in the soil is by flushing – pouring tepid water through the root substrate, be it compost/perlite etc., the amount of water should be twice that of the soil quantity.

Healthy Tomato Leaves

Above is the same plant two weeks later and you can see that new growth is now clear of ammonium toxicity after giving the roots a flush.

Mystery Item …

Edge of tomato grow pot
Guess this week’s mystery object -answers below please!

Testing One Two Three
I have a few tests and comparisons in mind, the links to which will appear this week in the navigation bar at the top of this page.

If you have any comments or suggestions please leave them below.

Best wishes,