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Growing Questions & Answers July 2019

Just a few questions this month. Aphid infestations, chilli peppers and a problem with potatoes.

Aphids in the Greenhouse

Barry has a problem most of us have this year – aphids. I noticed earlier we had more ladybirds around – a sure sign their food supply – aphids – were doing well.

Hi John
I have got a lot of greenfly in my greenhouse on my cucumbers. I keep on spraying the plants but I kill the aphids one day and the next day there are more of them. I don’t like using spray at any time, could you tell me what I can do?
Many thanks


Aphid Giving Birth
Aphids are actually born pregnant and adult female aphids can produce 100 offspring! They are mature in a week and then produce 5 baby aphids a day.
Photo: MedievalRich [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]

I don’t like poison sprays myself. What concerns me is the cocktail effect. Spray A is tested safe and spray B is tested safe but nobody is quite sure how safe a mix of A & B is. The physical contact killers like SB Invigorator do work – basically they smother the aphids. They’re not quite as effective as a poison would be but they’re 100% safe.

The problem is that any aphids you miss when spraying will repopulate the plant very quickly. You really need to be thorough when spraying. Don’t just spray the aphids you can see or the top of the leaves, spray under the leaves and the stems. Take your time, go top to bottom and slowly cover everything. You won’t get them all, but you’ll really knock them back.

You could try ladybirds – a ladybird eats about 5,000 aphids in her life! Great workers until the food supply (aphids) is eaten. Then they fly off to somewhere else in the garden. You can get a ladybird family from Greenhouse Sensations here.

One final thought – watch out for ants. They actually farm aphids for their honeydew. If you’ve ants in the greenhouse, use something like good old Nippon. It’s a poison but it only hits the ants and isn’t on the crops you eat.

How to grow Chilli Peppers

Ken’s wondering how I grow my chilli peppers.

Dear John please do you grow chillies? That being the case into large pots (I do not use plastic but terracotta) or directly into the soil?

Yes, I’m growing chillies. I’ve got some in the polytunnel border, some in large recycled plastic pots in the greenhouse and some in Chilligrows from Greenhouse Sensations. The plants in the Chilligrows are doing best by far. They are brilliant. A little bit expensive but they’ll last for many years.

Potato Problem

Nehanda has a problem with his potatoes dying off.

Hi John,
Thanks for the tips and offers. I am having trouble with my potatoes planted in the latter end of March, I don’t know the type of soil that I have on the allotment but after a good spurt of growth in early May the leaves are now beginning to turn a lighter green and some have turned yellow and died.
Do you have any inkling as to what the problem could be, please?

Best regards,

This is where some photos would have been very useful. Going by what you say, and assuming they’re maincrop rather than first earlies that may just be finishing, I suspect Mosaic virus. There’s no cure. Burn or bin the foliage to reduce infection next year.

BUT – it may just be a nutrient problem. Pale leaves and yellow leaves are often a sign of lack of nitrogen. I’d mix a couple of ounces of sulphate of ammonia with half an ounce of epsom salts in a 2 gallon watering can and using a fine rose (spray head) water around 10 feet row of plants. Don’t do this in strong sunlight. Early morning is best.

If it is a nutrient problem that should stop the problem and save things. It’s worth a try.

Posted in Allotment Garden Diary
2 comments on “Growing Questions & Answers July 2019
  1. Cleve Wicks says:

    Hi John,
    I have a big problem on allotment with marestail. Do you have any suggestion as to how I can reduce or get rid of marestail? Any assistance would be greatly appreciated.
    Many thanks

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