Answer: To space two different crops, figure the average of the two recommended distances, assuming they are going to be reaching full size simultaneously. So, your carrots could be about two and a half feet from your cucumbers.
Spacing can be manipulated in a number of ways. One of the most effective is to grow smaller plants in patches rather than rows. By limiting the amount of aisle, you preserve space for growing. For instance, you could grow about twenty or more carrots to maturity in a one foot square space, plus eat the carrots you thin out in the meantime.
To save lots of space, grow the cucumbers on a trellis. Also look for varieties described as bush, compact, or space saving.
Remember too that early season crops such as spinach will be finished early in the season and could be planted near plants that mature more slowly, such as tomatoes. The tomatoes will not need their full allotted space until well after the spinach is gone.
I suggest that you peruse some books on square foot gardening or French intensive gardening -- these techniques focus on maximizing a small space. Probably the best piece of information books like this provide is the potential yield of various crops...a 15 foot row of cucumbers or zucchini will produce a lot of fruit. Enjoy!
Q&A Library Searching Tips