Here is how I plan our heirloom garden. I draw up a draft of the garden, with rows. With a pencil, I plan where I want to grow each crop. My rows are 4 feet apart which allows for the crop to get large and I can still walk between the rows. This is mostly for the larger sized plants, such as tomatoes, potatoes, beans, peppers, etc. I double plant alot of rows. It works like this; I plant two rows of beans about a foot apart. Then there is a 4 foot space to the next crop. I do this also with potatoes. Small crops like lettuce, radishes, beets, onions, etc. are normally planted in our raised beds in rows 6-12″ apart. It is not necessary to have a 4 foot space between rows because in raised beds, we reach everything from the outside. We don’t need to walk between the rows. If I plant these smaller crops in a flat garden (no raised beds), I plant 2-4 rows 6-12″ apart and then a 4 foot space for a path. It is not necessary to have a 4 foot path on both sides of each row of onions, or carrots, etc.
I do not like to spend time weeding and hoeing and therefore, I eliminate paths whenever it seems expedient to do so. I like the garden filled to the brim with productive plants.
Also consider planting your rows north and south rather than east to west if possible. This helps the sun reach both sides of a tall crop like tomatoes. In my garden it is more convenient with the irrigation layout to plant east to west. I must consider, however, that the tomatoes and climbing beans will somewhate shade the row on the north side of them.
I draw this out on paper. Once I am content with the plan, I copy it onto cardstock and slip it inside a flat plastic bag. Then I can take it outside with me when I go to plant. Otherwise, you may run out of room before you finish. If you want to be sure that your rows are straight, take two stakes, one with twine or string wrapped around it. String it tight across the garden and hoe your trench for seed along the string. Then move it to the next row, measuring 4 feet on each end. My rows get a little crooked now and then, but when the garden is teeming with life and beautiful heirloom vegetables, the crooked row just never gets noticed!
I save the cardstock plan from year to year as a reference. Then I have an idea of how much I planted when I want to increase or decrease it the next season. It is also best not to plant the same crop on the same spot of ground year after year. Move the crops each year to discourage insects and disease that may be a problem if you grow a particular crop on that ground every year. I seldom worry about pest and disease. Treat your garden well (that doesn’t mean babysit 24/7) and it will abound with prosperity!