One of the reasons many of us may have for growing our own fruit and vegetables is because we wish to be sure our food is as unpolluted as possible. Whether you want to be completely Organic or not it seems fair to assume no-one actually wants to have more risky substances contaminating their soil and plants than can be avoided. After all they can be to no advantage and only pose a threat. But where do you start to reduce potential risks and which ones are worth worrying about?
Obviously organic gardeners are unlikely to be using many pesticides, and even those people willing to use pesticides ought to be doing it ‘by the book’. In fact a greater danger here comes from redundant pesticides, long since forgotten in the back of cupboards, leaking and contaminating all around them. The worst are those with lost labels. Many of the oldest were based on mercury, arsenic and lead and so may pollute for evermore. Post World War II pesticides were derived from nerve gases and are especially horrific. So anything old and especially if unidentifiable is best disposed of properly and NEVER burnt, buried or lobbed in the rubbish bin or down the drain- call your local council for advice on their disposal with as much identification as you can. And recently wood treatments traditionally considered safe such as creosote, tar and engine oil have all been deemed dangerous and now should not be used but disposed of safely. (Indeed anything potentially risky or poisonous should be evicted or locked up as children are far more at risk from these than they are from poisonous plants, mushrooms or berries. It is a salutary fact that for several decades significant numbers of children have been killed and injured by consuming household and garden products whereas during that same time not one has been killed by eating anything from nature. Most dangerous to them is putting liquids in beverage bottles as children may consume much of it before they realize it’s not good.)
Of course you can do little about the history of your soil and it could have been seriously contaminated in the past (SEE POLLUTION CONCERNS). Fortunately however this is not a common problem, and plants are quite cunning in taking up what they want and ignoring much else. Plants are even less prone to taking up contaminants if they are well supplied with moist humus rich soil and other nutrients are in plentiful supply. Thus adding loads of manure and compost, keeping the soil neutral with liming every so often and watering well will all give cleaner crops. And in fact it is the soil ON crops not the residues in crops that you have to worry more about. So washing and scrubbing, peeling and so on will all reduce any pollution levels considerably.
If you are worried by your soil’s history you can have it analysed. In the worst cases such as the site of an old chemical works, the topsoil may need to be removed and replaced. A big task but not as difficult or as expensive as imagined with the aid of modern machinery. (Those with an unpolluted but unworkable or difficult soil may also like to investigate the cost of replacing it with prime sieved loamy top soil.)
With less worrying contamination levels then covering the existing soil with a woven weed stopping fabric (to reduce worm movements bringing up soil from deeper) and then a new top layer of clean soil to grow in should suffice. Using weed control fabrics conventionally can further reduce soil contamination on crops grown through them by sealing everything underneath. Likewise thick mulches work nearly as well especially if continually topped up.
However you have to also consider possible contaminants you may be bringing in with your manures, mulches and composts. Obviously commercial ones; BF&B, seaweed, lime, sowing and potting composts should be clean though a shoddy supplier may let you down. Some builders merchants treat sand and gravel heaps with weed-killer! And it is hard to know exactly what you are getting when you order a truckload of this or that on the phone.
Well rotted farm yard manure is the ideal but from what? Over-fed pets’ and racehorses’ dung is likely to be good, even so it may bring with it all sorts of antibiotics, antiseptics and cleaning agents. But other manures may bring in more nasties. Certainly fattening animals are generally given less ‘nice’ food and ‘riskier medicines’ than breeding stock is, so choose muck from the latter if you can. Horse manure is considered safest, then sheep and goat, with pig being thought risky as it may be high in copper (often added to their feed). Chicken droppings have had high levels of Selenium as this was added to their feed. And likewise be careful with your pet and human wastes if you or they are taking antibiotics as these can contaminate crops as plants take them up from the soil. So stack and compost all manures well and for some time before you use them.
Never apply uncomposted bark mulches either as all sorts of diseases, and weeds may come in with these as well as possible pollutants. I stopped using sawdust from a sawmill when I found they used diesel as a cutting lubricant! (I was also smoking cheese with it and had wondered where the taint came from.) Some allegedly composted barks may really need re-composting. Likewise with leaves for leaf mould; ones from a busy roadside may be very dirty with oils, dusts and so on and maybe better avoided. And turf- one chap I know lost a load of bedding because he used the off cuts from his newly turfed lawn to fill his planters. This would have been good practice if the turf had not been from an old playing field and was full of broad leaved weed-killer residues….
Be careful of what you put in your compost heap as although the process can break down many contaminants it is unable to deal with some such as heavy metals. Glass, pottery, metal especially old batteries, foil, ring can pulls, perforated zinc and so on are all really foolish things to add to the heap and so to your soil. I know you would not- but watch what your family and friends add to the bin for them. Be particularly vigilant of donated bags of material as others will never be as careful as you would. Grass clippings from neighbours’ lawns that used weed-killers may be best avoided or well mixed into a well made heap. Do not worry about fruit and vegetable wastes and any pesticide residues in them as these are likely to be broken down by the composting, as are poisons such as the oxalates in rhubarb leaves.
Indeed you can compost almost anything that once lived but leather is full of nasties, wool and cotton are probably okay. Modern newspaper, ordinary paper and cardboard are safe enough but avoid too much glossy or heavily coloured material as that is pernicious. Some reckon adding the vacuum cleaner contents is risky because of dust brought in on your feet- so leave your shoes at the door... Soot used to be thought good stuff but is now seen as a mess of dioxins and other horrendous chemicals and best avoided.
However I reckon an area where most risky stuff may sneak into the garden is via the Bonfire. You know what I mean, there is a tendency to lob all sorts of things onto one when having a ‘tidy up’. Do not do so, or at least if you do then do not use the wood ashes as these will be full of nasties. In some countries it is now a crime to burn painted or treated wood. (One of the commonest undercoats was lead based and a common wood treatment was chromium based) Burning plastic is even worse and tantamount to poisoning your entire neigbourhood. Throwing any junk on a fire is seriously risky. Especially dangerous are old watches, clocks & automobile dials from fifty to hundred years ago as these have radioactive paint. Electrical items may have lead, mercury and many many other nasties. Most older electrical appliances have a lot of asbestos in them. Surprisingly so does much of that old thick textured plaster-finish for ceilings and walls, and even some lino-like floor coverings.
Do remember that a hot fierce fire of dry material burns cleaner and causes less air pollution than a smouldering damp pyre. Of course you wouldn’t be daft enough to breathe the smoke but try not to let it fall on your soil or plants either by getting air in under the fire by raising it on irons supported on bricks.
Even without a bonfire the air is full of dust, and all sorts of chemicals and disease spores. Some herbicides especially the hormonal ones have distorted vines and other crops when droplets arrived from unbelievably great distances away. A thick windbreak especially a sticky leaved poplar belt if you could ever run to one, an evergreen hedge or two, or a trellis covered with a dense climber will filter much of the floating stuff out before it reaches you. The more trees and hedges the better for all of us. A good filtering screen is especially important between you and a road or railway as the dusts and oils from these are potentially very hazardous.
Rain is not pure either, the rain is full of dirt though usually not enough to worry, remember how snow darkens as it melts. Worst is a roof that has accumulated dust for weeks on end and then gets some little rain. This will make a very dirty run off, with bird droppings and so on, making it unsuitable for splashing on salads and fruits even if diluted in a huge butt. So be careful to apply rainwater to your soil not the plants! There are gadgets which fit on the down-pipe which bypass the first very dirty flushing and then allow the cleaner bulk to go to the tank. Lead and copper corrode and iron rusts so inspect your roof and where permitted paint over exposed metal. (I’d use black bituminized or similar waterproof paint or a clear lacquer)
Watch out for dripping oil or petrol from your mower or power tools, and a petrol leak may be a fire hazard as well as a pollutant.
Then there is the general detritus. Don’t add to your existing litter. And remove it before it breaks up into more bits. Be careful of plastic in particular. I have not yet seen a plastic pot, gizmo or watering can that does not eventually start to deposit small shards of brittle-ised plastic here and there. Bin them before they appear everywhere. Plastic sheet used for cloches or ground cover is pernicious once it starts to go. As are video/audio tapes used for bird scarers which not only break up but also shower off their magnetic coating. Thank goodness cds seem to be replacing these.
-And what about car tyres and old carpets- well I admit to using both. Car tyres are remarkably stable and have outlasted all the plastic tubs I acquired at about the same time. In fact it is the dust off tyres that is more of a threat, I have seen it quoted that eight tons of rubber dust from worn tyres is deposited on London every day. As to carpets, well in the past I used them as temporary weed-killing mulches but the modern woven ground cover fabrics are better, cheap and second hand carpet has become too expensive to use in the garden. Of course some folks have given carpet a bad name as they have been silly and left them down for long periods to become a problem on some allotments and been banned. One council even claimed carpets were so full of pollutants ‘walked in’ from the street that they should not allowed in gardens. We’d better keep them in the house then……..