Laudator Temporis Acti

Robert Frost, Putting in the Seed:

You come to fetch me from my work to-night
When supper's on the table, and we'll see
If I can leave off burying the white
Soft petals fallen from the apple tree.

(Soft petals, yes, but not so barren quite,
Mingled with these, smooth bean and wrinkled pea;)
And go along with you ere you lose sight
Of what you came for and become like me,

Slave to a springtime passion for the earth.
How Love burns through the Putting in the Seed
On through the watching for that early birth
When, just as the soil tarnishes with weed,

The sturdy seedling with arched body comes
Shouldering its way and shedding the earth crumbs.

Frost apparently planted his beans and peas around apple blossom time. This is a good rule of green thumb. See, e.g., Daniel Lindsey Thomas and Lucy Blayney Thomas, Kentucky Superstitions (Princeton: Princeton University Press, 1920), p. 219 (#2884): "When apple trees bloom, plant beans."

Perhaps Frost also planted the beans and peas right in an apple orchard, between rows of trees. See Michael Phillips, The Apple Grower: A Guide for the Organic Orchardist, 2nd ed. (White River Junction: Chelsea Green Publishing, 2005), p. 26:

Our great-grandparents often planted berries down the rows of a developing orchard. That way, they could enjoy several seasons of small-fruit production from the cultivated ground before the orchard trees filled in their allotted space. Beans provide both a marketable crop and nitrogen fixation on their leguminous roots. Such interplanting is an appropriate form of biodiversity, so long as the soil is built up and protected. Vegetables such as potatoes or winter squash can be followed with a cover crop rich in organic matter. The planting aisleway decreases in width as the tree roots seek out the enriched earth. Shallow cultivation here does not overly compromise young trees, because permanent roots that are encouraged downward access moisture and subsoil nutrients. The resulting good tilth from added organic matter more than compensates returning feeder roots with rich humus. Deliberately leaving crop ground for vegetable production between every few rows of orchard certainly abets airflow. Letting go the notion of a solid-block orchard — "Monoculture or Bust" — allows more management options on a diversified farm. Small orchards will reap diversity benefits from nearby borders of native plants in addition to the creative expression provided by crops interplanted between the trees.

Id., p. 106, n. 32:

Peas, beans, squash, and late potatoes work well in the early years of a wide-row orchard. Choose annual crops that require cultivation but don't require excessive soil enrichment.

Jasper Francis Cropsey, Apple Blossoms