The differences between green and string beans are easy to remember because they don't exist. The designations "green" and "string," when applied to vegetables of the Phaseolus vulgaris species, refer to exactly the same plants. To confuse matters even more, they're also known as snap beans. What distinguishes them from other beans is their time to harvest, which is when their pods are still green and and filled with immature seeds.
Snapped and Unstrung
In days gone by, the stringy fibers running down bean pods' seams, or sutures, were manually removed. The bean stringer twisted one of a bean's tips until it snapped, pulled it down the seam to unzip the fiber and repeated the exercise in reverse with the other tip. Except for heirloom bean varieties, the fiber and snapping are no more; thanks to decades of hybridizing, modern green beans have no strings attached. Their alternate names, however, refuse to die.
A Snap to Grow
Whatever you choose to call them, string, green or snap beans are the ideal vegetable for non-green thumbs. Plant their seeds after the soil temperature reaches 65 degrees Fahrenheit.
The Planting Site
Plant bean seeds where they'll receive at least six hours of daily sun. A well-drained spot with loose, sandy loam soil is best. If heavy, water-absorbing clay is all that's available, amend it with a 3-inch layer of organic compost.
Loosen the upper 6 inches of soil with a spade or rotary tiller. Break up large clods and remove stones or other debris.
Distribute the compost evenly over the loosened soil, using the wheelbarrow.
Till the compost into the soil until the two are thoroughly incorporated.
The Planting Process
To plant the seeds, run the corner of a hoe along the soil in a 1-inch deep furrow. Plant the seeds about 2 inches apart and cover them with the removed soil. Firm the soil lightly with the flat side of the hoe, and then water well. For a large crop, space multiple furrows 12 inches apart.
Keep the soil moist until the seeds germinate. When the seedlings reach 6 inches, mulch around them with a 1/4 inch layer of herbicide-free grass clippings, replenished with fresh ones as they die down.
As legumes, string beans pull nitrogen from the air and channel it to root nodules, or bumps, filled with the soil-borne Rhizobia bacteria. The bacteria change the nitrogen into a form the plants use to manufacture their pods. Thanks to this collaboration, beans grown in organically rich or compost-amended soil rarely need extra fertilizer.
Like other vegetables, string beans typically need 1 inch of rain or supplemental water per week. Increase the amount when the average temperature -- figured by adding the daytime high and nighttime low and dividing the total by 2 -- exceeds 60 degrees Fahrenheit. Give the beans an extra 1/2 inch of water for every 10 degrees the average climbs above 60 F.
As an example, when the highest weekly daytime temperature peaks at 98 F and the weekly nighttime low is 80 F, for a total of 178, the average temperature is 89 F. That's almost 30 degrees above 60 F, and the beans need another 1 1/2 inches of water, for a total of 2 1/2 inches if it hasn't rained.