Answer: Straw bale gardening is the ultimate in soilless gardening. You can use one or dozens of bales as you need and in any pattern. Because straw bale gardening is raised, it's easy to work with, so make sure you allow for handy access.
Wheat or oat straw is best - it is the stalks left from harvesting grain so it containers very few seeds. Hay bales are less popular because they are made of whole plants with lots of seeds and often other weeds in. Use what you can get locally ? it may even be lucerne or pea straw bales.
Put the bales in the exact place, because it's too hard to even nudge these monsters once you've got your little straw bale garden factory in full swing. You'll get one good season out of a bale and usually two, albeit with a bit of sag. It makes for great compost or mulch when finished with.
Lay them lengthwise to make planting easy by just parting the straw. Make sure the string is running around each bale and not on the side touching the ground in case it's degradable twine. Keep the twine there to hold it all in place and if it does rot, bang some stakes in at both ends.
Starting off with slightly aged bales of about 6 months is best, but if they're new, thoroughly soak with water and leave for 5 or so days while the temperature rises and cooks the inside, then they will cool and be ready for planting. They won't be composting much inside yet, that takes months, but you don't want that initial hot cooking of your plants.
Your biggest task will be to keep everything well watered. Straw bale gardening uses more water than a normal garden, so be prepared. It may be that dumping a bucket on it each day will be enough in your area, or you may need to keep the hose handy.
Best wishes with your garden!
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