In this newsletter, we’ll discuss various types of potting compost for tomatoes and whether or not to feed seedlings. How not to kill our seedlings and plants with kindness!

Compost – the earth in bags from the garden centre!

Where there’s muck there’s brass – the old saying is true when it comes to buying compost. It is expensive and large pots and containers need lots of it!

If you get to the garden centre and the bags have been outside in the rain and snow since the end of last season, they’ll probably be soaked through and if they are, they are not worth buying. Look for bags that are under cover or bags you are satisfied have dry contents.

Potting Compost for Tomatoes

There are two ways to go, John Innes which is expensive and heavy stuff or multi-purpose which you can usually buy in quantity for a discount – three bags for two is a popular way to buy. Because John Innes is so good, manufacturers have started adding it to multi-purpose compost so you can now buy a mix of both.

John Innes compost

A type not a brand, is high quality and specially formulated for the different stages of a plant’s development and growth.

It comes in the following mixes:

  • Seed Compost is for sowing seeds
  • Cutting Compost is for rooting cuttings – you can make cuttings of tomato plants too!
  • No 1 Potting Compost is for pricking out young plants
  • No 2 Potting Compost is for potting on.
  • No 3 Potting Compost is for established plants.

Loam is the major ingredient in the compost as it provides the main “body” of the compost. It is composed of silt, clay, and organic matter in evenly mixed particles of various sizes. More fertile than sandy soils, loam is not stiff and difficult to dig like clay soils.

Because it is porous, it allows high moisture retention and air circulation.

Loam also contains essential micro-elements and some organic matter which provides a slow release of nitrogen to the plant.

Sphagnum Moss Peat increases the total porosity and improves both the aeration and the water-retaining capacity. Peat decomposes slowly into humus.

The use of peat is an issue from a conservation point o view, so alternatives are often used – coir for example.

The coarse sand or grit is used as a physical conditioner to allow excess water to drain from the compost and thus prevent water-logging. It also helps to provide stability for larger plants.

Added Nutrients

The compound fertiliser in John Innes Compost provides a wide spectrum of plant nutrients needed for balanced growth, including:

  • Nitrogen – for top growth
  • Phosphorus – for root growth
  • Potassium/Potash – for flowering and fruiting
  • Trace Elements – for vigorous growth, colour and flavour

The fertiliser is usually sufficient for around five weeks of growing, after which time additional feed should be given, but it also depends on the size of the container and the amount of compost used.

Multi-purpose compost can consist of any of the above ingredients so it is “pot luck” (sorry about that!) what you get in the bag although the contents are sometimes displayed on the bag.

Multi-purpose should have the same nutrients as John Innes.

Conditioning of multi-purpose compost for tomatoes

Sand is an excellent additive to compost if you grow in large pots, because it not only aids drainage but also adds weight and so makes the pots less likely to blow over in windy weather. A few bricks or heavy stones in the bottom of a pots can achieve the same results.

A further addition to the mix could be perlite. This helps aeration, drainage and it also (most importantly) helps stop grow bags and pots from drying-out as it retains moisture.

Traditionally, grow bags were the cheapest way to buy compost but as grow bags seem to get smaller and smaller these days, a big bag of multi-purpose on a three for two deal can be more economical (if you can manage to lift it!).

Feeding Seedlings

Feeding seedlings is unnecessary if they are kept in good growing conditions. However, tomato plants like people, suffer from stress when they are transplanted – similar to moving home – and a feed at this time can help the transition.

This would be done with organic liquid seaweed solution or a general purpose food at half strength like Miracle Grow.

Being too generous to young plants can damage their roots. If temperatures are low, tomato plants are unable to absorb nutrients anyway!

Tomato food should only be given later on, when plants are flowering or fruiting.

Next week is the start of the “sow-a-long” and if we’re successful, will become a “grow-a-long” – I think I had better stop there!

Also, in next week’s newsletter we’ll discuss how to get a good crop of tomatoes even in a poor summer – such as last year!

11 Responses

  1. Jessie Allaway
    | Reply

    Hi Nick,

    Regards from Argyll. Hope you are well these days.

    My tomato plants are growing at snail speed this year and I have been blaming the lack of even a small amount of peat in the compost. Most of them still in 5″ pots. I was very late in sowing this year but even so had expected them to have caught up by now.

    My question is would it be OK to add something to water to gee them up like a weak dose of seaweed fertiliser to plants that are still quite small? Usually don’t feed until first flowers but they would be in full size pots by then.

    Would appreciate your advice.

    Best regards
    Jess Allaway

    • Nick
      | Reply

      Hi Jess,
      It’s good to hear from you and sorry for the late replay too!
      Yes, I feed my plants liquid seaweed at every stage of growth to encourage disease resistance and friendly soil microbes etc.
      Sometimes plants don’t respond as expected and there doesn’t seem to be a good reason why!
      Still, the weather is pretty good around the UK now, so maybe your plants will pick up a bit.
      Best regards,

  2. Joe
    | Reply

    Hi, I have been growing tomatoes in doors since Jan this year , they are about 9” high is it to early to put in un heated greenhouse, also I grew tomatoes in a 5’ x 20” trough last year , very successful I might say , can I plant tomatoes this year in the same trough , thank you

    • Nick
      | Reply

      Yes, but I recommend you change the soil by replacing with fresh compost.

  3. derek starkey
    | Reply

    just bought some potting compost by westland says on the bag ( with added john innes ? any good

  4. Derek
    | Reply

    Exciting stuff as always, I intend to be a part of this though I’ll be a month late coze I’m still working on saving seed from my last crop of tomatoes and two more variaties havnt yet ripened 🙁

  5. John
    | Reply

    Thanks for the info Nick. What % sand would you add to multi purpose compost ?

    • Nick
      | Reply

      I like to add a couple trowel-fulls of sand to the compost in the lower area of a large container or pot.
      This adds weight to help prevent pots from being blown-over in windy conditions and helps drainage.

      The % would be about 10% in the lower half of the pot.

  6. juliette.bravo
    | Reply

    Also looking forward to sowing-a-long! Thanks for so much useful info – I am hoping that this year, with the benefit of your weekly newsletter, I might reap the fruits of my labour! Thanks.

  7. Andy
    | Reply

    Looking forward to sow a long, grow a long and hopefully pick lots nice tasty tomatoes a long. I’ve tried growing some maskota (spelt wrong I think) and wilma but think i started too early and they’ve got very leggy and most of the wilma have died. Hope the guide will help us as we often get plants off a friend but have ordered most of the easy varieties you’ve mentioned and will give it a go armed with our propogator and greenhouse. Looking forward to your next blog.

  8. Roy Abbott
    | Reply

    You give some interesting information about composts here Nick thanks for this.

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