This year I decided to try one of the new weed-stopping fabrics in my plot at Southwark/Queen Village Garden. Actually, I did manage to put it down in the path between my garden and the fence. I've not yet got it down anywhere else. Everything got in the way: work, weather, bedding plants that had to get planted before they got too old, etc. So I can't really report on whether the stuff keeps weeds down, much less on whether it is at all effective in keeping moisture in the soil. The only thing the package says is that you can water through it - and, I guess, use water soluble fertilizer. Anyway, it is a new thing to try.
Biodynamic, French intensive and many traditional gardeners believe that a vegetable garden should be watered daily. The way it works is that you start when soil moisture is still good and, using a watering can or a water breaking hose attachment, water your growing area just until the soil surface is shiny when you stop. This kind of watering, particularly on raised beds or raised rows, keeps the whole depth of the soil moist from the very deepest part to the surface. It's great - if you start early and keep on keeping on. But if you neglect your daily (or twice daily) watering for a couple of days in dry weather and haven't put any mulch down, you get problems. The nice ''column" of moist soil from the surface down is cut, and the plant's roots can dry out near the surface. Not good for the plants. Not good at all.
Lots of other folk recommend watering deeply once or twice a week in weeks when we don't get at least an inch of rain. (And when was the last time we had that - at least in South Philadelphia?) This encourages the roots of your plants to grow deep into moister parts of the soil and thus be less stressed by dry weather (or occasional neglect). Penn State's Urban Gardening Program even has a watering guide based on this idea and on when each vegetable needs water most to make sure it produces best. You can get a copy by calling 560-4167.
Putting a mulch down on soil that's moist from the surface down 6-12 inches will help hold that nice water column so plants can depend both on deep and near surface roots during a dry spell. It also saves you both water and work - a great idea in July when we get very little rain and the heat and humidity are enough to discourage practically anyone. But before you put the mulch down, you absolutely have to be sure the soil is moist. If you're going to use black plastic, especially, the soil has to be nice and moist. If it is not, it can just cook under that plastic.
If you have the money, you can lay an irrigation system under your mulch. The easiest sort would probably be a soaker hose laid down a row or two hoses dividing a bed in thirds. When you turn your water on, it will go to the end of the hose and then seep through the tiny pores in the hose and water the plants' roots, period. No water will get lost or wasted by evaporating into the air. No water will splash on the soil and then splash upon the plant carrying diseases. No water will be left on the leaves as a place for fungi to land and breed.
Recyclers who can get hold of PVC plastic pipe can drill tiny 1/16-1/8 inch holes in it and cap the ends and use it in much the same way as soaker hose. Just be sure to drill your holes down both sides of the pipe.
Myself, I think it may be a bit late this season for most folk to go with irrigation systems like these unless they're still gardening in rows. It's really easy to lay drip hose or pipe or whatever along the rows and attach them to a "header" pipe or hose along one short end of the garden. But if you've moved on to growing in beds, it may be a bit more difficult to put in an irrigation system after the fact. My beds are not in nice lines, and jumping hose or pipe across my paths would be a real problem. If I decide to go this route, I'll just have to redesign the beds and do some extra digging in the fall or early next spring. A really good soak and mulch is possible, though, and should drought-proof both the backyard and my Southwark/Queen village plot "tolerable well". Besides, we all voted to close the office Friday, so there will be both gardening and partying time.