I live in what is reputedly the driest village in Great Britain. East Anglia supposedly gets 24 inches of rain a year, mostly falling during winter and Bank holidays, in my garden I've measured a scanty 16-20 inches most years. Although I make every effort to save and store my rain and have a shallow ground-water well I never have enough water. Irrigating my greenhouse and polytunnel crops and watering plants in containers obviously takes priority, so a recurring problem has been summer water shortages which have restricted the yields of open ground crops.
As droughts have long been a problem here even in the years before hosepipe bans elsewhere I soon noticed many drawbacks with using copious quantities of tap water when I could do so. Adding tap water with a sprinkler, encouraged weed seeds to germinate, facilitated slugs and snails moving around, chilled the soil by application and by evaporation, and introduced chlorine and salts the soil could well have done without. More importantly I begrudged the inconvenience and time taken to water throughout much of the growing season. Certainly more water gave bigger crops; I found the most convenient and effective way was trench irrigation but with the arrival of water meters this has become prohibitively expensive. (Oh but you should see the results!)
From the start I had mulched some areas heavily but generally had restricted this to initial and permanent plantings such as around new trees and shrubs and in the fruit cage Although I was aware of the water retaining capacity of mulches I was mostly using them for their weed control not for saving watering. However I became more and more impressed by their beneficial results, not only with the much diminished need for water but in the increased fertility and most surprisingly the better pest control achieved.
The moistness under any mulch demonstrates the water saved from evaporating away. That moist soil is also throbbing with life which would be dormant or living deeper down if the soil was drier. The greater activity in the soil over it's whole depth is also abetted by the less extreme temperature range induced by the mulch and thus the soil becomes more alive and more fertile. This is increased yet further as most mulches are themselves degrading so adding new material to the process. The foliage of heavily mulched plants could be seen to be darker and they endured droughts better and for longer than similar ones nearby in bare soil.
Mulched plants generally seem to suffer fewer pest attacks and this may be because the plants are not under water stress. Pigeons continue to be a problem and mice can increase under a mulch, as unfortunately do slugs. These latter were never a problem here with my bare soil (sand and dust). Mulches, excepting cocoa shell, encourage slugs and these can prove troublesome for a few crops during damper periods. I use slug pubs whenever necessary and plant prone crops under plastic bottle cloches or within cut out plastic rings. The weed control obtained from a thick mulch means little weeding and I notice that as a surface is less disturbed more creatures move in, particularly ground beetles and spiders which are voracious predators and as these thrive so the slugs dwindle.
For several years I tried various mulching materials with differing degrees of success in different parts of the garden. Some were more or less suitable for different purposes but one in particular has proven itself effective and, more importantly, cheap enough for really widespread use, and that is straw. Traditionally straw is mostly employed for earthing up rhubarb and mulching round strawberries, however I have found it can be used more extensively over almost the whole vegetable garden.
At first I used straw as a thick mulch under and around semi-permanent crops such as beds of Jerusalem and Globe Artichokes. As I had noticed with plants in the fruit cage the plants became much healthier in leaf and produced bigger and better crops with no weeding or watering. Over the years I started deep straw mulching between sweet corn, brassicas and under tomatoes, marrows and courgettes. Even in the greenhouse and polytunnel I have found a straw mulch useful and it keeps the crops, and knees, clean. Straw makes excellent paths as it is neat, light, does not stick to the feet and dries very quickly on the surface after showers.
Soon I decided to reverse my method and instead of mulching piecemeal I covered my entire vegetable grounds, paths and all, in a very deep straw mulch. Four rows of ten beds each four foot wide by sixteen feet long with one foot paths between each bed and two foot wide ones between the rows were covered with one hundred bales to four to six inches deep. The only beds that were left uncovered were two of overwintering onions and two with green manures. From then on I have only exposed the soil when necessary for sowing and have continued to top it up liberally. Each autumn another forty or fifty bales are added.
Laying straw mulches on still days obviously makes sense and spraying them with a hose afterwards helps the straw settle. Straw could blow around when being laid, this is no problem in a fruit cage but in an open garden it risks a mess - though birds and worms seem to clear it all away fairly rapidly. Birds can mess it up themselves but in critical areas can be prevented by holding down the straw with light plastic netting. I have been happily surprised by how well a straw mulch resists even high winds once it has settled.
I use wheat straw bought from a non-organic farmer, I would prefer organic straw but this is unobtainable. To minimise residues I buy old straw bales that are somewhat weathered, wet or degraded and stack these for six months before use so they are partly broken down. New straw is cleaner, but not allowed under organic regulations, and costs much more! (Barley straw has irritating awns but otherwise behaves similarly as does hay which unfortunately attracts most slugs, fresh grass clippings are high in nitrogen and behave completely differently.)
Straw mulches are alleged to cause nitrogen robbery and so are usually accompanied by a recommendation for a prior dressing of nitrogen such as blood, fish & bone meal, I find this unnecessary. True if any high cellulose material is mixed into soil the microlife breaks it down at the temporary expense of fertility, but this cannot occur whilst it remains on the surface as a mulch. Although a straw mulch can incorporate at a phenomenal rate there appears to be no significant robbery unless it is accidentally mixed in and I suspect this is because it is processed differently when absorbed only at the soil surface, presumably it is chewed up by worms and wood lice etc.
The best attribute of straw (other than cheapness) is that although it retains moisture in the soil underneath it also allows rain to pass through much more easily than do mulches such as well rotted manure, composted bark or mushroom waste. Thus although light showers get absorbed heavy rain, when any does come, easily penetrates deeper. Wherever my soil is necessarily bare it forms a crust which throws off rain, and it cracks which allows the runoff to then run to waste. Under the straw mulch the soil surface stays open and absorbs the water.
One drawback with a permanent straw mulch is a slight delay in the soil warming up in spring, this is a serious handicap for asparagus. For most other crops though this can be counteracted by covering the mulch with black plastic for a few weeks before sowing. Some crops such as onions also seem to prefer bare soil around them to grow and ripen properly, the same goes for haricot drying beans, and carrots and radish do best for me in small blocks. For all of these I rake the straw aside, the tilth revealed is excellent, and quickly warms up ready for sowing. With most transplanted crops such as brassicas, sweet corn, leeks etc. I find once they are established the straw mulch can be repositioned closely around them.
Indeed I find most of these last crops can even be grown straight through a deep straw mulch. Obviously one must part the straw a bit to plant or sow but this can be done without disturbing the rest of the mulch. I find the smallest, and those direct sown plants, are best given a plastic bottle cloche or ring until the time they have grown above the straw. Bigger transplants are easier and may use the straw for initial support while they are limp. Early sowings such as rows of peas enjoy being in the sheltered valley excavated through straw which helps keep the spring winds off them while they are tiny. At the other end of the season I use a thick straw mulch under a plastic sheet to store root crops and cabbages in situ- they then keep fresh throughout winter.
Long ago I had tried the Lawrence Hills no-dig potato method where you earthed up the potatoes with straw rather than with soil, for years I used a modified version of this employing grass clippings as they also fed the spuds. In most years I found potatoes that were mulched early on were later than those grown in bare soil but earlier mulching saved more water and gave better yields. I also noticed that volunteers growing through the new permanent straw mulch were a little late but they gave a big crop if left, almost certainly due to the greater retention of the winter rainfall. In bare soil I had previously tried autumn planting of potato sets but had experienced too many losses in cold winters. With the straw mulch as added protection the volunteers came through, so I realised it could equally protect an intended crop. Thus I then planted last year's potato seed in the autumn as that year's crop were dug, choosing the best sets I planted them four to six inches deep in the soil on a new bed and recovered them with straw. The great majority survived the winter, flourished and harvested a good crop - all without any attention whatsoever. No trenching, no earthing up, no weeding and no watering. Now if I could only get them to dig themselves up .... .