Too much nitrogen
Nitrogen drives leaf growth. Too much of it, from rich manure, lawn feed or a high-nitrogen fertiliser, keeps a plant growing leaves at the expense of flowers, fruit and roots. It also makes soft growth that aphids and mildew favour.
Soil & nutrients
What it looks like
The plant looks superb, which is exactly the problem.
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Big, dark leaves Foliage is deep green and larger than normal. -
Few flowers Plants grow on and on without budding. -
Hairy or forked roots Carrots and parsnips in freshly manured ground fork and grow whiskery. -
Soft, sappy shoots Growth is lush and attracts aphids.
How to confirm it
Look at what went on the soil, and rule out heat.
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Feeding history
Fresh manure, lawn feed or weekly general-purpose feed points to excess nitrogen.
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Check the weather
Peppers and tomatoes also drop flowers in heat; research shows heat is often the bigger cause.
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Compare plants
Plants in poorer soil nearby flowering well supports the diagnosis.
What to do
Stop the nitrogen; the plant will turn to flowering.
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Stop feeding
Hold off all nitrogen feeds until flowers appear.
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Switch to potash
Use a high-potash tomato feed on fruiting crops once they start to flower.
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Be patient
A heavy dose keeps pushing leaves for several weeks.
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Plant roots elsewhere
Next year, sow roots in ground manured for a previous crop.
Prevent it next time
- Manure the bed a season before root crops, not just before.
- Use balanced feed early and high-potash feed from flowering.
- Grow lavender, herbs and nasturtiums in lean soil.
What not to do
Do not add more fertiliser to a leafy plant that will not flower.
In the growing guides
Where the guides mention it, with plant-specific advice.
Sources
- Pepper production problems, University of Illinois Extension
- Fertilisers, Royal Horticultural Society