In Kitchen Garden Feb 05 I discussed watering and ventilation under cover where we have almost complete control and in May 02 I examined various ways of applying water. Now I'm turning my attention to the quality of the water. In the open ground it is possible to get away with rarely if ever watering anything. I have successfully sown, transplanted and grown many crops in my dry East Anglian soils without any additional water other than our sparse rainfall. Obviously without added water the timing of such operations is crucial and yields suffer. When water has been freely available and applied the timing of these operations becomes more flexible -and yields multiply significantly especially with certain crops such as sweet corn.
The problem is that rain does not fall when you want it and there is rarely enough saved up rain water to cover the needs of the average productive plot. Gardeners are then exasperated by hose pipe bans just when we need to use them most. Other sources of water are sometimes turned to as they can be used to advantage but either because of oversight or worries about pollution many of these may go untapped. Of course even the freshest rainfall is not pure water and other sources carry even more pollutants, so the question becomes which source is more suitable for what?
Rain may carry significant amounts of dust –remember the falls of red sand blown from the Sahara some summers ago. Bacteria, spores, viruses and seeds are all deposited by the rain which is far from sterile and is probably the main source of infection of tomato and potato blight and cucumber mosaic diseases. Rain also carries some fertility in the form of dissolved nitrates especially after thunderstorm activity. I've heard it said snow is even richer and it certainly seems to have a beneficial effect beyond the effect expected by the water content alone.
Then as you store water it changes, anyone who has an old butt full of leaves will know just how revolting such stagnant water is. A tea made from manure or plant materials may be of benefit to some plants but sour stagnant water is unlikely to be very beneficial to many. The main reasons may be heightened acidity which may harm some roots, a burden of pathogens especially wilts and moulds but also the deoxygenated state.
Plant roots need oxygen as they work differently to leaves and continually breathe out co2 and breathe in oxygen, They die and rot when waterlogged primarily because of a lack of air. Using sour stagnant water may relieve water stress at the cost of damaging the roots. However this is much more of a problem under cover and for plants in pots and containers rather than for those growing in the open ground. Even so for the latter such water can be ameliorated by adding garden lime to neutralise the excess acidity, and by applying it with a rose so it aerates to some extent as it breaks up and runs into the soil. Try and avoid getting foul water on foliage, stems or on soft or young growths especially seeds and seedlings or they are almost guaranteed to damp off.
Of course if the water butt is clean and the rain water in it relatively fresh then it is safer to use on more risky subjects but even so best kept from actual contact. If held in a warm butt such as inside a greenhouse then even apparently clean water soon becomes potentially full of pathogens. Thus although rain water is in itself preferable I reckon it safer to use tap water along with all the accompanying lime and chemicals for misting, spraying and sprinkling almost anything indoors or out. As I also keep goldfish in my water butts then I add some suitable oxygenating weeds and I find these keep the water clean and free of gnats –but it still carries a risk of pathogens.
Likewise with water from a ditch or pond. Hardly pure and as well as being a source of nutrients it may be a source of nasty human as well as plant disease and infection. So it should be used with care and given to the larger and more robust again and avoiding the young and delicate. Be careful if there is a slow flow and no bottom vegetation, be especially careful if it whiffs of either excrement or detergent. And do not use it on salad crops!
At least butt, pond and ditch water tends to be close to ambient temperature and not so cold it chills plants however water from a ground water or deep well can be very cold and would be better for warming up in a butt overnight before use. This is crucial for plants under cover but a cold chill does not help those in the open ground either and should be avoided. Well water may also have a load of unwanted pollutants and or fertility depending on the depth and ground structure. In chalky areas well water may be so hard it leaves residues on leaves etc. when it dries and can block pores and look unsightly. Of course tap water in the same area may well do likewise. Stone fruits, grapes, melons and brassicas love lime so they have no problem, most vegetables like it in moderation though blueberries and cranberries cannot tolerate it and need rain water. Watercress needs running clean alkaline water and if you have a source is a valuable crop.
One problem of hard water does not usually occur in the open ground in the UK but with pots and containers especially those outdoors in windy areas. Large amounts of water have to be added to cope with the evaporation and transpiration requirements. As each batch of water is used up it leaves behind it's load of lime and other salts which slowly build up and soon poison the compost. Signs of this are a crusty salty coating on the compost surface or on the outside of clay pots, and often brown tips to leaves. The best cure is to wash the compost and pots thoroughly with sufficient water to wash away the surplus salts and to apply only rain water thereafter.
A source of useful if polluted water is grey water from the house. I find that bath, shower and washing up water can be redirected to fruit trees and other perennial crops to advantage. However the place where it runs to soon becomes stagnant and unpleasant from the soaps, fats and debris carried in the water. The solution is to run it for only a few days at a time into a network of shallow scraped out troughs above the roots of this or that crop. Then to move the outlet to another set of troughs elsewhere and to immediately rake back down the first trough walls to cover the slimy residues which locks in the moisture and seals away their decomposition into fertility most sweetly.
Water from the average dishwasher or washing machine carries too high a load of residues to be used safely even in droughts. It is possible that by using lesser amounts of safer more natural detergents then even these grey water sources could be used but at the moment it seems of dubious quality and safety. –Mind you I don't even have a dishwasher.
I have heard of people so keen to keep some plants watered with the appropriately pH balanced pure water that they have selected a particular bottled water for their treasures. Of course most kitchen garden crops are not worried by a bit of lime and indeed benefit from it however if you happen to have a collection of blueberries what else are you to do when the rain water butt runs out? Well defrost the freezer -that ice that has formed on the inside of a freezer compartment is not sterile but it is almost pure -tease it off and melt it in a plastic bucket and you can have pints of the equivalent of distilled or de-ionised water for free, and your freezer will run much more efficiently for the clearing. And also if you have an air de-humidifier or an air conditioner; both of these condense out large amounts of almost pure water which ought not go to waste.
And then of course there is the difficult question of which desperate crop gets which water first?
Well obviously existing crops in containers must have the first call and those with a swelling crop of fruits most urgently so. The younger and smaller seedlings and plants in pots and the open ground also need water more than their older brethren simply because their root systems are so much smaller they can tap less soil. As said earlier these also need the warmer and more sterile waters rather than the cold and rank.
Although it is possible to sow in dry soil and hope the rain comes it is the next most crucial watering of all. Water the ground thoroughly the day before you intend to sow so that it has soaked in and warmed up. For this I prefer tap water not rain simply because it takes so much. It would be foolish to use anything but clean rain or tap water for soaking the actual drills. Even if you pre-soaked the ground it is a good idea to soak the sowing drills long enough before sowing for the water to drain away again. Thus we can ensure there is enough moisture in the soil to not only germinate the seed, see it through to emergence but then to get it's roots down deep enough to find it's own water.
Secondly it most important to water most plants before transplanting them so they have reserves to last till they re-establish. Again it helps to plan so you do this the day before the operation. And do water the new site and planting holes also at the same time, again so they have time to soak through, aerate and warm up before the new plant arrives. The bigger and stronger and older the plant then the less pure water can be used more safely. Such as leeks, celeriac, sweet corn, runner beans, blackcurrants and comfrey revel in unpleasantly dirty water once they get going. However it is very dubious practice to use really foul butt, pond or house water on such as seedlings which will probably collapse - and any salad crops. Do not contaminate the foliage you are going to eat! Salad crops really do deserve only tap water for the sake of hygiene, and because of plant viruses and bacteria in rainwater likewise it is safest to use tap water for tomatoes, potatoes and cucurbits.
Third crops in flower respond really well to a good watering when you see their flowers, and as they are established most will be happy with fouler water than when they are younger. In order of value I would give water first to potatoes and sweet corn, then peas and beans. It is barely worth watering the onions or roots, or brassicas once they’re established.
Finally comes everything else which fortunately being mostly perennial can cope with well water and other grey sources. I have rarely seen much benefit from watering most soft fruit in the ground after it's first year of establishment. I think the reason is the fruits swell fairly early before the soil water is depleted most seasons though on very dry sites raspberries and their kin can really suffer. Obviously the bog loving blue and cran berries need plentiful water, blackcurrants are happy in a ditch liking plenty of water -but don't actually need it so wet. Grapes should never need water! Strawberries are a moot point as I reckon they taste, and jam, better when grown on the dry side though the crops are lighter.
Much of the top fruit being more deeply rooted tends to do better from a good mulch early on and judicious pruning and thinning than from any added water except in droughts. But pears are an exception and need a moister soil than any other top fruit save quinces and mulberries, these three all may fail to hold crops in dry soil. This makes them good candidates for the grey water from the house or sludgy tank and they may share it in rotation.
And when you reach the bottom of that barrel and you get that sludgy black smelly gungy watery mess -don't put that anywhere but on the compost heap.