BALES: Worked for us to grow right on top of rocky, root filled soil. We planted tomato starts and nasturtium seeds using older bales. Still they heated up when we wet them, so we waited 2 weeks & added compost to planting holes. The soil under the bales has improved enough now after 2 gardening seasons that garden space is usable for vegetables and though still rocky soil we remove as we encounter them. For your slope it depends on what you want to plant. If you add finished compost and/or soil to your planting holes it might work fine. LEAVES: In my climate we have a lot of large maple leaves that are super slow to decompose without shredding or adding greens. I use them to make leaf mold and/or as mulch. We recently gathered about 30 bags from an apartment complex, emptied bags on lawn & mowed over them with mulch mower. Used in garden as mulch and bagged up about 10 bags to use in spring for composting projects or as mulch again. I like fewer bags to store, but didn't like the amount of work we created for ourselves once we dumped ALL those leaves. I don't think I'd do it again, so your plan to just them rot is much easier!

I copied this from an article in a small rural newspaper while travelling. Not all new gardeners can count on cultivated soil for their plants. Some may be burdened by limited space or rocky ground. As a result, whether a new gardener or a veggie veteran, bale gardening may be the way to go. Growing vegetables in bales really works because bales provide the two things seeds need to grow. "For seeds to germinate, all you need is heat and moisture," said John Sims of the Farmer's Cooperative. In 2005, The Post published an article on bale gardening, and it has been one of the most frequently read articles at The Post Online. Tomatoes, peppers, squash, cucumbers, green beans, melons and a host of other plants grow well in bales. The Farmer's Cooperative, Southern States, and Danny's Builder Supply in Centre all carry wheat straw bales. To plant a hay bale garden, first, around 10 days before planting seeds, place the bales in a sunny location. Soak them with water for three days. On the fourth day, apply 5 oz. of fertilizer, followed by a couple more days of watering. On the seventh day, apply 2.5 oz more fertilizer, followed by a couple more days of watering. On the 10th day, apply a cup fertilizer and lightly water into the hay bale. On the 11th day, plant seeds by applying a three-inch layer of top soil or potting mix to serve as a bed. Each bale can hold two tomato plants, four pepper plants, six to eight cucumbers, three yellow squash or 12-15 bean seeds. Bales can typically be used for two or three seasons.

Update: I found a source listed in another thread. Sorry for asking an already answered question. Island Farm Inc 417 2nd Avenue West, Seattle, WA 98119

I have done it the last 2 years. I grew potatoes in bales and tomatoes. I threatened to do squash, but it never happened. I tried cabbage last fall but that was a complete bust. My husband didn't think the potato yield was good enough, but it was the year of the monsoon spring rains and other peoples potatoes were drowning, so I thought we were lucky to get any. The reverse is true though, you have good drainage, so they dry out faster. With tomatoes it was like growing them in very deep mulch. As soon as the roots hit the soil below the straw, the tomatoes obviously did better. I was not unhappy with tomatoes grown in straw bales. It gave me room for more plants, and they are taller to work with, like you say. Last year I had 5 bales together with long sides butted against each other. Nothing grew in the center bale. My theory was it got too hot, so consider that in your plans. A row of bales end to end did not have problems like that. I think you could get away with rows 2 bales wide. In my experience, the inside of the bale does not turn into compost, at least not in time to be useful. I seasoned the bales as recommended, too. My method became cut a hole in the bale wide enough for a transplant and fill it with potting soil. The roots can grow down through the potting soil into the ground below. Tomatoes can be planted lower in a modified version of planting them deeper in dirt. Alternative method is to pry the flakes apart and put a transplant in the straw. It is too hot and dry here to put 2" of soil on top of a bale and expect things to survive in it. Not even alyssum. Unless you want to water twice a day and fertilize because you're flushing all the nutrients through. I've seen pics where everything is growing happily in the bales and flowers in the sides, etc. The only thing I can figure is it's not as hot and gets more rain. While I didn't think they broke down into compost, the bales do deteriorate over the season. If you want to hold them together better you might wrap chicken wire around them for support. I don't want to discourage you from trying this. Like I said, I got to grow a lot more tomatoes than I would have otherwise. I think we may have to learn to adapt the method to our climate. I will be interested to hear how squash and cukes do with this method. I may even try squash in a bale this year.