It’s a busy time of the season when there are a lot of tomato plants to pot into their final position. It’s also expensive if there are so many large pots to fill with new compost. so using old compost for tomatoes is very tempting!
Sometimes grow bag soil can work out less expensive than bags of multi-purpose compost – a quick calculation is often needed when choosing which compost to buy.
Using Old Compost for Tomato Plants
If like me, you have too many plants and plenty of old compost left over from last season, you may like to try an experiment and use some of the old stuff from last season’s large pots.
Remove the top layer – the weeds and seeds
Tip out and expose to the sun for a week or so (solarisation)
Dig and get plenty of air in the soil
Fertilise with any or all of the following:
- Fish, blood and bone
- Chicken manure pellets
- Slow release fertilisers
- Grow Char – Carbon Gold
- Seaweed Extract
- Fish Emulsion (Bio Bizz)
- Home made teas
If that lot doesn’t rejuvenate old soil, nothing will!
By growing disease resistant varieties, usually having the the suffix “VFN”, we can further prevent our plants from getting diseases from old soil.
The only caution is if your plants suffered a serious disease last season such as blight, it’s best not to re-use the soil they were growing in.
Of course most of my plants go into new compost mixed with perlite – we all know how important oxygen is for plant roots!
Growth Limiting Deficiencies
A lack of nitrogen is the main reason why plants may grow slowly. If your plants need more nitrogen they will display pale green leaves, yellow leaves at the bottom of the plant and even flower buds may fall off.
Another growth limiting deficiency is phosphorus. This is displayed as a purple tinge on the underside of leaves. The plants and leaves become stunted and the leaf surfaces are a very dark green.
Both of the above nutrient problems can be caused by keeping young tomato plants in their small pots for too long.
A time scale that works well is:
- Three weeks in the seed tray
- Three weeks in a smaller pot – 3 inch or 3 and a half inch (9cm).
- Three weeks in a bigger pot – around 5 inch.
- Plant in final container/grow bag – container size around 10 to 15 litres (around 3 to 4 gallons).
This means that if we sow in mid March, the plants will go into their final container towards the end of May after the last frost.
Why use so many potting stages?
I’m often asked why we use so many potting on stages – why we don’t just plant directly in the ground.
Apart from the slugs, snails and diseases associated with garden soil that would kill our vulnerable plants, when roots feel the sides of a pot the plants mature more quickly. The trick is to push them on without them becoming root bound or lacking an important nutrient as in the example above.
Protection from the sun
Garden fleece is very useful at this time of the season for covering plants on cold nights and protecting seedlings from direct sunlight during the midday sun.
When sunlight is too strong for a plant, it will sometimes turn or bend a leaf branch away from the light.
Here’s an example of a Bejbino cherry variety bending a leaf branch down and away from the hot sun.
Thanks to Buster for the very nice plants!
That’s it for this week … I’m spending the rest of the day tomato-ing!
Protect seedlings from direct sunlight with garden fleece.
Pots dry out very quickly in the sun – if going out for the day make sure plants have plenty of water or put them in partial shade.
It’s good to reduce the strength of liquid feed in hot weather because plants need more water than food.
Wilting plants should be put in the shade and misted with water.
Using old compost for tomatoes is best avoided, unless it is given the treatment mentioned above.