Problems with Tomatoes not growing

[JacquiParticipant]

On 3rd March I sowed three varieties of tomatoes , Mr Fothergills Sungold F1, Suffolk Herbs Martina and Kings Seeds Red Zebra in Expanding Coir pellets in a heated propagator in a greenhouse.
On 24th March all varieties had grown sufficiently to be potted on.
They were potted on into small pots in Melcourt Sylvagrow Sustainable Growing Medium and placed back into the heated propagator for a few weeks.
Then placed on a bench in the greenhouse covered with a propagator lid on cold nights.
I noticed recently that they do not appear to be growing or very slowly.
I have tried watering with a dilute seaweed feed.
Today I have removed some from their pots and noticed the roots seem very thin and rather sparse.

What is the cause for the slow growth? Could it be the compost.
Should I repot them in a different general purpose compost.

I have gown these varieties before in this way but normally start the seeds off in mid February. Any Advice please.

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[Don FoleyParticipant]

Hi Jacqui, At 10 weeks from sowing these should be 30 – 40 cm high.
From your dates it seems they have been in these small pots for 7 weeks.
I would suspect two things. Overwatering and lack of nutrients.
Overwatering will cause the roots to die back. The plant is trying to stop itself drowning.
The overwatering will also wash out the nutrients from the compost faster, which in those pots would have run out in 3 – 4 weeks anyway.
I would suggest moving them on to slightly bigger pot, maybe 3cm bigger, with fresh compost.
I would also suggest planting deeper – up to where the first leaf comes off the stem. This will encourage fresh root growth from that area of stem currently exposed.
Try a different compost just in case what your using is suspect though if it were you would have had problems with other seedlings?
Water from the bottom to try and encourage the roots to spread downward.
Check the roots again in about 10 days when you should observe fresh root growth.

Don.

[RhysParticipant]

Definitely sounds like compost issues to me Jacqui.

I sowed my tomatoes on April 7th this year and my Sungold and Zenith had been transplanted twice by day 19 as they grew so fast. It was a very sunny April here, but I just potted on into local garden centre own-brand MPC with a smidgen of rock dust, fungi and friendly bugs and all nine strains grew like the wind. They had to be held back indoors for a few days in early May when the nights were 3-5C, but they were in final pots this year after 5-6 weeks.

If you have space inside to keep 12-18 8cm pots on a sunny windowsill, growth in the first four weeks can be very rapid indeed with later sowings. I have experimented sowing from early Feb to late April and the only reason to sow early in my experience is to deliberately get a crop in mid to late June. If you intend putting into final positions in mid May, plants will be plenty big enough sown in early April if they mostly live indoors.

Obviously if they live in a greenhouse, things may be a bit different.

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