Problem Solving

Problem Solving

Every season brings its own problems and each year can be different from another. This is part of the joy of gardening. However there are several problems which can occur each year but with careful propagation and planting these can be avoided.

As vegetables are to be eaten it is advisable to use as few chemical sprays as possible. There are products available which can be used up to harvest and will kill pests such as aphids and whitefly with no ill effects. It is worth watching out for these in the garden centres.

Make your own natural garlic sprays.

Use this simple garlic repellent to deter garden pests like aphids and slugs. It can also help eliminate powdery mildew on foliage.
Peel the cloves from a whole head of garlic and put in a food processor or blender with 235 ml of water. Purée the mixture (this takes about a minute in a regular food processor). Alternatively, chop or crush the cloves as finely as you can by hand and mix well with the water.
Add a further 700ml of water to the mix, along with 30ml of any liquid soap. Blend again and then transfer to a clean jar.
Leave the mixture to steep overnight, or for at least 12 hours, so that the garlic can infuse the liquid with its potent sulphur compounds.
Once the mixture has had time to steep, strain it through a muslin cloth or fine mesh strainer to remove the solid garlic pieces (which would otherwise clog the nozzle on your spray bottle).
Pour the garlic-infused liquid into a reusable spray bottle and store in the fridge between uses.
Mist plants in the evening, holding the spray about 15-30cm away from the foliage, and cover both sides of the leaves with an even coating of the garlic pesticide spray. Reapply every few days (and after any rainfall) when your plants are suffering with an infestation, or once a week as a deterrent.

Garlic has a reputation for warding off vampires but it’s also effective against smaller blood-sucking creatures such as mosquitoes.

Add two-three crushed fresh garlic cloves to a food grade oil such as sunflower oil, and leave to infuse for 24 hours.
The following day, add 1 teaspoon of fresh lemon juice to the mixture, along with 500 ml water.
Strain the garlic, lemon and oil mixture through some muslin cloth or a fine mesh strainer to remove the pieces of garlic.
Transfer to a spray bottle and apply this natural repellent as needed to keep mosquitoes away.


For control of Onion Fly remove onion as soon as symptoms occur and destroy before the maggots go into the soil to pupate.

To control Downy Mildew on onions. Increase the spacing of onions to improve air circulation around the plants and keep them weed free. Thrips can be controlled by a spray with permethrin or garlic concentrate spray.

White rot is perhaps the most serious of the problems as there is no chemical control available. The infected onions must be lifted and destroyed. Remove the soil that the onion was growing in. Do not store or re-use this soil but dispose of it. The ground can then be given a thorough cleaning by using a soil sterilant.

When onions run to seed it is usually due to climatic conditions causing a check in growth.

There are several new varieties of onion which are white rot and mildew resistant. These are well worth trying if these are a problem. However the large onions are not resistant so care must be taken to give plenty of space between the plants.


Leek rust is perhaps the number one problem on any leek bed. Keep the ground weed free and remove any leaves with high number of spores..

For Thrips on leeks spray as for onions but using a spreading agent.

When spraying leeks always use a spreading agent to make sure the spray stays in contact with the leaves. N.B Soft soap works as a spraying agent.

Leek Moth is an increasing problem in some parts of the country. Sadly there is no approved spray to kill this pest. Careful hygiene to remove any left over leek debris will help. Also anything which will catch the moths before they lay eggs it is the grub which does the damage so pheromone traps or the common garden spider can help.


Slugs can be a major problem especially when growing for exhibition as the celery blanching paper makes an ideal home. Clean and remove the slugs every time a new blanching band is added and keep a regular supply of slug pellets around the plant. If pellets are not your preferred choice use one of the many alternative methods available.

To reduce Heart Rot we have found a dressing of calcified seaweed in March or a drench spray with a weak solution of calcium nitrate can help.

For Celery Rust spray with a copper-based fungicide and remove any infected leaves.

Celery is also prone to carrot fly, so here again companion planting does help.


Root Rot is caused by bad drainage so choose the site carefully and rotate the crop. If there are no or very few flowers there is too high a nitrogen presence in the soil, use a well-balanced feed. This also applies to flowers that drop. Under watering also affect flower drop. To help the beans to set, water well when the flowers are in bud.

A problem we have not experienced but is increasing in some areas is Bean Rust. This is worst in a warm damp summer. We cannot recommend a spray but would suggest that the leaves be removed promptly.


To avoid the problem of Downy Mildew, practice good rotation. As Powdery Mildew usually only attacks late in the season it is often not worth bothering to control.

For Foot Rot on peas spray with a fungicide spray at the first sign.

Always try to grow peas on new ground, that is ground which has not grown peas in the previous year.


The major problem with growing all types of Brassica in a small garden is Club Root. To avoid Club Root we suggest using a good crop rotation. Keeping the lime content high can also help.

Caterpillars can be either sprayed with an insecticide such as permethrin or removed by hand. If left, they can devastate the crop.

Cabbage Root Fly Maggot can be deterred by a ring of carpet or roofing felt to deter the fly from laying the eggs in the base of the stem.

White Blister is encouraged by warm humid weather. Avoid growing brassica on infected soil as it can persist in the ground. As there is no effective control available we suggest any leaves be removed and destroyed at the first sign of the blister.


Diseases are far more important than insect pests on tomatoes. Tomatoes grown outdoors are much less susceptible to disease than ones grown indoors. Keep a careful watch on indoor crops and treat plants immediately.

Poor drainage will cause Root Rot. The roots below ground are brown and corky; the top will wilt in hot weather. The root rot cannot be stopped once its taken hold. A mulch on top of the ground will help the formation of new roots.

Root rot can be treated if the plant is slightly affected. Treat the affected area with Cheshunt Compound. This is usually a disease of seedlings or young plants.

Stem Rot or Didymella is a disease of mature plants of which there is no effective treatment. This can be spread from plant to plant by watering or by handling. The fungus can over winter on debris or in the soil. It is essential the soil be well cleaned or sterilized before tomatoes are grown on the same area.

Tomato Blight is a devastating disease of tomatoes and is an increasing problem in some areas of the country, care must be taken to destroy all green matter to prevent a follow on infection. Wash or destroy any canes used in the growing of tomatoes with Blight. There are some new varieties which are Blight resistant which are worth trying if Blight is a continuing problem.

Unlike potatoes rolled leaves on tomatoes do not indicate disease. The curling of young leaves is usually taken as a good sign if they are dark green. The rolling of older leaves is usually due to a wide variation between day and night temperatures. Providing no pests are present no action need be taken.

Either too much heat or too little potash can cause blotchy fruit. The glasshouse can be shaded to reduce the heat, use a high potash feed. Blossom end rot, which causes the end of the tomato to turn black, is due to irregular watering when the fruit is setting and can be problem when using grow bags. To avoid this ensure a regular water supply to each plant.

Two of the main pests that attack tomatoes are Whitefly and Aphids. Both can be treated effectively either by predators or an insecticide spray. We have found predators work extremely well; they work continuously throughout the season.

Pepper/ Aubergine

Peppers, both sweet and hot, and Aubergines can suffer the same type of problems as tomatoes. The same solutions apply. Always allow sufficient ventilation for the plants and check regularly for aphids, whitefly or glasshouse spider mite. If found, as with tomatoes use either an insecticide spray or predators.


Root Rot is when the plants appear to be growing well then collapse. This can be caused by over watering on cool damp days, or the more common reason, not using new clean compost. Once the plants have collapsed nothing can be done to restore them.

Botrytis is caused by to high humidity for the heat in the greenhouse, increase ventilation on these days.

Bitter fruits can be caused by slow growth; we suggest an increase in feeding. Open pollinated varieties, such as King George, can be bitter if the fruits have been pollinated. To prevent this all the male flowers should be removed.

To prevent Mildew on cucumbers ventilate on all possible occasions. Keeping the floor of the greenhouse moist also helps.

Marrow, Squash & Pumpkin

Very few pests will attack these. Any Aphids can be removed in the usual way. Mildew can be controlled by a spray. Although does not usually become a problem till late in the season.

If the fruit does not set this is usually an indication of the ground being too rich.


Canker is the main problem when growing parsnips. This however can be caused by several factors, soil acidity, irregular watering or the presence of too fresh organic matter in the soil. As there is no spray to counteract Canker careful ground preparation is a must. Lime the soil regularly and pay careful attention to watering, particularly when growing long parsnips for exhibition on raised beds or in tubs.


Very few pests attack this vegetable. However they can be prone to the usual attacks of Aphids so a careful watch should be kept for any infestation. Long beetroot are usually sown in raised beds therefore there is little chance the seedlings will get Black Leg, this is a problem usually associated with wet ground.


Aphids can be a serious pest as not only do they make the plant sticky they can also spread mosaic virus. Spray with insecticide at the first sign, taking care to observe harvest dates.

Like most other vegetables lettuce can bolt if they receive a check in growth. However if they reach maturity without being used they will bolt, so it is advisable to sow or plant only a few at a time.


Carrot fly is the main pest for carrots. The fly is attracted to the carrot by the scent. A good method to prevent an attack is to spray with garlic concentrate this works well to disguise the smell of carrots. Use companion planting to hide the carrots. Avoid disturbing the carrots during growth, sow thinly to avoid any thinning out, leave the weed to hide the crop. Cover the carrots with horticultural fleece or grow them in a raised bed. When growing long carrots for exhibition in a raised bed there is less chance of them being spoilt by carrot fly.

Stony soil or ground that has had fresh manure applied can cause forked roots.


One of the main problems with potatoes is blight. It is a devastating condition.  At the first sight of brown on the leaves remove the tops and destroy. Plant hygiene is of great importance. Do not compost or store any tops with blight on. Take them of site completely or burn as soon as possible to prevent a follow on infection.