Germination and compost for tomatoes – comparing the progress of seeds sown in:

  • John Innes Seed Compost
  • John Innes + Vermiculite 50/50
  • John innes + Perlite 50/50

Sown Sunday 17th February 2013 – Day 1

Test One
Three varieties were sown in rows, with one seed in each cell. Space is left between cells to increase air movement and light.

The reason for the test is to show that by adding vermiculite or perlite to seed compost at a rate of 1:1 will increase healthy growth.

Seedlings should also be able to stay in a 50/50 mix longer and remain healthier than in compost alone – we’ll see as the weeks progress!

One Week Later … Sunday 24th February


The first seedlings to germinate are growing in the John Innes Seed Compost (left column). They started to come through after just four days at around 20c.

The middle column contains 2 out of three seedlings – one seed is taking its time or has failed to germinate. This is the 50/50 John Innes/vermiculite.

In the right column, 50/50 (John Innes/perlite), the seedlings are all coming through but a little slower than in the John Innes.

Very impressed with the John Innes seed compost but as the seedlings grow and need more oxygen for their roots, I think that the addition of vermiculite and perlite will show its value.

Two weeks after sowing … Sunday 3rd March

Test One Week 3

Two seeds have failed – the fault of the seeds rather than the compost I think.

No notable differences yet.

Three Weeks After Sowing … Sunday 10th March

Test One W4

All about equal still.

Four Weeks After Sowing … Sunday 17th March

Four weeks from sowing

There is very little difference between the seedlings but perhaps the JI alone has slightly larger seedlings.

What I would say is that a finer media (seed compost alone) is better at the earliest stages when roots are very fine.

However, as seedlings develop, media containing a mix with more air (by adding vermiculite or perlite) is better for growth.

Over-watering the fine seed compost would have a negative effect on the roots.

I intend to transplant these seedlings now into their own pots 50/50 compost/perlite, so the test is over.

Adding V or P to the seed mix has no significant beneficial effect in the first four weeks of growth – though it would help to prevent over-watering.

Vermiculite and especially perlite definitely will improve growth of older plants (five weeks plus), but that’s to prove in another test!

Go To Test Two


Please note:
The best time to sow in the UK is from mid March to the end of April.
Unless you have grow lights, or are very experienced, sowing in the middle of February is not recommended because light levels are too low and plants may become very leggy.

If you sow later than April, you will need a quick growing cherry variety like Red Alert in order to get ripe fruit before the weather turns cold.