I have been surprised this week about the number of gardeners who have called me in regards to problems they are having with potatoes, tomatoes, beans and roses.

Generally the problems have all been along the lines of distorted or unusual new growths on otherwise very healthy looking plants.

The cause, in all cases, has been the resultant spray drift from the use of chemical herbicides such as Roundup or lawn weed killers, or the composting of lawn clippings that have weed killer residues still present.

It only takes minute amounts of a chemical weed killer (and we are talking about parts per million) to have an effect on the most vulnerable plants such as roses, tomatoes, potatoes and beans. These very small amounts can cause the plants to produce very unusual, distorted new growths. In many cases, the effects will grow out over time unless the amount of the weed killer is sufficient to kill the plant completely.

Other plants in the area including weeds will show no outward signs of a problem though you can bet in some way their growth is also affected.

One case I heard was the gardener who had used Tordon on the lawn to kill the weeds and then composted the clippings. Later the composted material was applied to the vegetable garden. The results were the beans distorted when they germinated and the tomatoes showed similar problems.

The best advice is not to compost grass clippings that have been treated with a weed killer for six months and the safest way to dispose of the clippings is to a landfill or place under well established trees and shrubs where the residues will not harm the plants.

Green recycling sites that take in organic material for recycling have no way of knowing if the pile of lawn clippings in a trailer contains herbicides or not. If the material does contain weed killers then there may be problems for the unsuspecting gardener who purchases the end result as compost.

Another situation that can occur from time to time is a farmer spraying a paddock for thistles or other weeds with a spray that does not kill the grasses. Later, sheep or cattle are let into the paddock and their manure can be lethal to tomatoes and other vulnerable plants if used in gardens. If collecting manure from a farmer, it is advisable to ask if he uses herbicides.

However, there is an easy way of testing compost from either a recycling site or manure from a farm. Simply place a few bean seeds into the material and germinate them. If they come up neat and normal then the material is safe to use around sensitive plants.

Herbicide spray drift is another big problem and many gardeners believe that the best time to spray a weed killer is on a calm day when there is no breeze.


This is one of the worst times to spray as small droplets of the spray are lifted up into the air on the conventional air currents and will float up to later drop somewhere, which maybe on your garden or someone else’s.

The best time to spray a herbicide is when there is a mild breeze so that you can direct the spray away from the non target areas. Even granulated weed killers that are applied dry and then watered down can possibly cause problems as the moisture from the broken down granules can be lifted into the air to move to non target areas.

Another “don’t” is never use the same sprayer for both weed killers and other sprays.
The plastic in sprayers absorb some minute amounts of the herbicide which can be released later when spraying your roses or other plants. Have a sprayer that is clearly marked, Weed Killers Only. I don’t know how many times I have come across the problem of a weed killer contamination in a sprayer that later has wiped out a lot of plants in the garden. Even if you diligently wash out a sprayer used for weed killers it will still have residues at parts per million.

The safest way is to never use chemical weed killers but then you may have to do a lot more work keeping areas free of weeds. At the same time you cannot control what the people do next door or down the road. If you know that the people are using a weed killer some where near your home you can protect your vulnerable plants by spraying them with water to further dilute any residues. A broadcasting sprinkler system for this is ideal. Run it for a short time every couple of hours that day till dusk.

In my books I give a number of safe methods of controlling weeds using common products such as salt and vinegar which will not cause any problems to non target plants.

The best time to control weeds is just after they have germinated, they are nice and small and very vulnerable to a sharp knife scrapping across the soil where they are growing. If you want a good healthy soil structure do not pull out common weeds, instead slice them off with a sharp knife just below soil level and leave the foliage sitting on the top of the soil to naturally break down.

Don’t walk on growing areas of gardens as this compacts the soil. Create walkways so you can tend growing areas.

Don’t cultivate the soil by digging or using rotary hoes. Instead, cover areas with wet newspaper, use compost along with other goodies such as animal manures, sheep pellets and blood & bone and then plant into this top level. (Some disturbance of the soil such as forking up potatoes will be needed but should be kept to a minimum.)

Watering: light watering with a hand held hose using a filter to remove chlorine from the water (if applicable) should be done daily unless it has rained. Regular light watering to keep soil evenly moist is another key to successful gardening. Do not flood areas as this disrupts soil life but on the other hand never allow areas to dry out too much as that is as bad as flooding.

Watering is an art and once learned, will make for great healthy gardens.

Watering by hand gives you time to relax and check plants for either disease or insect pest problems. This means you can treat the small problem quickly before it becomes a big problem.

Don’t waste your money on lots of man made fertilisers as these will not give you great gardens with healthy plants.

Do use all natural fertilisers such as dolomite, gypsum, animal manures, Rok Solid (mineral dust), Ocean Solids (minerals from the seas) and Magic Botanic Liquid (MBL) which will enhance the soil and plants. The latter, when sprayed over the foliage of plants every couple of weeks will turn a so-so garden into a great garden.

Every week I have gardeners who contact me to say they have adopted some or most of my suggestions for gardening and that their gardens have never been so good.

It’s just common sense and don’t be swayed into what has become known as conventional agriculture with its chemical concoctions. That form of gardening is outdated now, unsustainable and a heavy drag on your wallet.

Please ring me with any problems on 0800 466464 or Palmerston North (06) 3570606. Email:

One comment on “DO’s AND DONT’s IN GARDENING

  1. What’s the matter with preparing the soil by digging it over?

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