Potting Compost for Tomatoes

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.

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/Soil
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.

Peat
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.

Sand
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

Fertiliser
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!