Answer: Some gardeners have had success using or experimenting with this technique. They will plant the seeds or transplant into a handful of good quality compost stuffed into the top layer of the bale, water it, and watch the results. The hay bale is left intact with its ties and just sits on the surface so you could theoretically do this on a paved surface. Over time it will begin to rot and the plants' roots will work their way down through it. You may need to continue with a steady fertilization program using a water soluble fertilizer and topdress periodically with compost for best results, also water as needed to keep the material slightly damp like a wrung out sponge. Hay bales may contain a lot of weed seeds so you may prefer to use straw instead, or allow the hay several weeks to sprout their surface seeds prior to planting. An old leftover bale from last year should work fine as it will already be partly decomposed. At the end of the season your bale will be pretty much composted, so you can add it to the compost pile, use it as mulch, or dig it into the garden as a soil amendment. Here is one gardener's description of what worked. You may need to cut and paste the complete url into your browser to make it work correctly.
I hope this helps.
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