What Will Fit in a Straw Bale?

I learned the hard way last year that there is only so much that can reasonably be grown in each bale of a straw bale garden.  The problem I ran into is that there seems to be much space available when planting, leading to an urge to plant more than the bales can reasonable sustain.  There are many resources on the interwebs that warn against this and offer reasonable numbers of plants per bale depending on what is being planted, most of which I would consider a bit conservative despite my over-planting issues of a year ago.  I just went way, way overboard.

So here is a list of what I plan to plant in my bales for Straw Bale Garden 2012, dependent on what crop is being planted.  Of course I don't claim to be any sort of expert on the subject, what with only a year of experience under my belt, so take these numbers with a grain of salt.  Of course numbers may vary quite a bit for some crops, so be sure to take into account the description of what size your plants will end up being.  No matter what, try not to plant bigger plants like tomatoes too close to the edge of the bale or it will become unstable when it grows large.

1. Tomatoes - The conservative number here is two plants per bale, but I think most varieties can probably fit three plants as long as the tomato bales themselves are spaced apart from each other.  In this case I would zig-zag the plants in a V-shape across the bale to space the plants as far apart as possible.  
2. Cukes/Squash/Things that grow on vines - This type of plant really is more dependent on what space you have available for the vines to ramble, but assuming this is not too much of a constraint each bale should be able to accommodate upwards of four plants.  Three might be better though if the plants are going to be wide ranging, as bigger plants will consume your bale more quickly and hurt the harvest yield.  Cukes and summer squash in particular can be trained to climb a bit so keep that in mind to save ground space.  Winter squash have huge leaves and seem to crowd-out other vines competing for the same space.  I ordered one variety of cuke this year called "Spacemaster" that I am hoping will mostly stay atop its bale.  I think anything advertised to be good for planters on your porch/deck are just right for straw bales.
3. Peas/Beans/Etc. - These can be planted very close together and I think 12-15 plants per bale are easily accommodated for most varieties.  I had 15 wax bean plants in one bale last year and they did very well.
4. Spinach/Loose Leaf Lettuce/Other Greens - I plant these in pretty thick by scattering the seeds on a prepared bale, then thin them out as they grow in.  This worked very well last year, with the thinned leaves and shoots creating the base for really wonderful salads.
5. Peppers/Eggplants - Unless they are really large plants, six in each bale should be fine.

Things I am not experienced with directly, but can make a good guess at:

• Broccoli/Cabbage/Head Lettuce - Probably six plants would work well, possibly eight.
• Corn/Sunflowers - I wouldn't try these at all, personally.  2-3 plants for each might be feasible if the ground your bales sit on is very flat.
• Root vegetables - These are not supposed to do well in bales.  I think the nature of the substrate would not allow for normal growth of things like carrots, potatoes, etc.

There are probably some types of plants I am forgetting to include, but this list should be a good starting point.  I think the best answer though, is just to realize how big your plants will be when they are fully grown, and don't be tempted by the tiny size of your seedlings to add more and more.

Happy gardening.