How to build a Three Sisters mound

The Three Sisters is corn, beans, and squash grown together on a raised mound. The mound and the planting order are the parts people skip, and they are the parts that make it work. Here is how to shape one and plant it, and where the honest limits are.

What the mound is for

A mound is a low, raised hill of soil. Raising the planting area a hand's width above the ground warms it faster in spring and drains it better - both of which the heat-loving corn and squash want in cool, wet soils early in the season. In a dry climate the advice flips: a raised mound sheds the water you need it to hold, so growers there flatten the top and press a shallow saucer into it to pool irrigation. (Extension sources describe the warming and draining; treat it as a sound reason to mound, not a precise, measured yield effect.)

How big to shape it

Two common sizes, both from extension guides - pick by how much room you have:

• A small hill: about 30 cma foot high and 45–90 cm18 inches to 3 feet across, holding 3-4 corn plants. Space hills 0.9–1.2 m3–4 feet apart, in every direction.
• A larger mound: a few feet wide, holding 7-10 corn plants.

Whichever you build, the corn's spacing inside it and the gaps between mounds are set so the whole patch reads as a block - which the next section explains is not optional.

The layout the planner produces

This is a Three Sisters bed laid out by the planner - the corn in its block, the beans at the corn's feet, and the squash filling the gaps between the mounds, exactly as the placement rules compute it:

• 36 × corn
• 27 × common bean
• 4 × summer squash

The corn must be a block, not a row

This is the single mistake that ruins a first Three Sisters bed, so it leads here. Corn is wind-pollinated: pollen falls from the tassel at the top and has to land on the silks below, and a single decorative row lets the wind carry most of it away - you get ears with gaps where kernels never formed. The fix is to plant corn in a block of several short rows so the pollen has neighbours to land on:

Well established

Corn requires a block of at least 4 rows (roughly 12 plants) for adequate kernel set.

fatal if ignored → block

Mechanism: Maize is wind-pollinated and protandrous. Tassels shed pollen that must land on silks of neighbouring plants. Below roughly 12 plants in a block of at least 4 rows, insufficient pollen reaches enough silks; each unfertilized silk is one missing kernel.

Evidence: confirmed against 4 sources in the research-based literature.

the 4 sources

UMN Extension, 'Growing sweet corn in home gardens', extension.umn.edu/vegetables/growing-sweet-corn (read 2026-07-11): 'Always plant corn in blocks of at least four rows. Corn planted in a single row will have much of its pollen blown out of the row, and will produce ears that have blank areas where kernels did not form.'

NC State Extension, 'Organic Sweet Corn Production' (Horticulture Information Leaflets), content.ces.ncsu.edu/organic-sweet-corn-production (read 2026-07-11): 'Corn is wind-pollinated and should be planted in blocks of at least 4 rows for good pollination to occur.'

UMD Extension, 'Growing Sweet Corn in a Home Garden', extension.umd.edu/resource/growing-sweet-corn-home-garden (read 2026-07-11): 'Plant in blocks of at least three to four short rows, rather than one or two long rows, to ensure good pollination; minimum of three rows side by side (preferably four rows).'

Clemson HGIC 1308, 'Sweet Corn' (updated 2023-01-23), hgic.clemson.edu/factsheet/sweet-corn (read 2026-07-11): 'This crop is wind-pollinated; therefore, plant in blocks of several rows rather than 1 or 2 long rows to ensure full ears.'

remedy

Plant in a block of at least 4 rows, or omit corn and substitute a trellis.

Read the full rule → · open in the planner ↗

Cluster your mounds together for the same reason - a tight block of hills pollinates; a line of them strung out does not.

Plant in order, not all at once

The three don't go in on the same day. Each gets a head start before the next would crowd or shade it, and the corn in particular has to be strong enough to carry the beans before they climb:

Well established

A vine assigned to a living support must be sown after the support is established — corn ~6 in (~15 cm) tall, roughly 2-3 weeks — not at the same time.

costly if ignored → warn

Mechanism: Load. A bean vine on an immature, poorly-anchored stalk pulls it over; extension guides key the delay to the support's height (corn ~6 in) as a proxy for it being rooted enough to bear the climbing load.

Evidence: confirmed against 2 sources in the research-based literature.

the 2 sources

Cornell Garden-Based Learning, 'How to Plant the Three Sisters', gardening.cals.cornell.edu/lessons/curriculum-classics/the-three-sisters-exploring-an-iroquois-garden/how-to-plant-the-three-sisters (read 2026-07-11): 'When the corn plants are about 6 inches high, pole beans and pumpkins can be planted around the corn plants.'

USDA National Agricultural Library, 'The Three Sisters of Indigenous American Agriculture', nal.usda.gov/collections/stories/three-sisters (read 2026-07-11): 'Two or three weeks after the corn was planted, the women returned to plant bean seeds in the same hills.'

remedy

Sow the vine 2-3 weeks after the support, once it is about 15 cm tall.

Read the full rule → · open in the planner ↗

In practice, over about three to four weeks:

• Corn first, once the soil is warm (around 13°C55°F). Sow 5-7 seeds per hill, 2–3 cman inch or so deep; thin to the sturdiest 3-4.
• Beans next, when the corn is about 15 cm6 inches tall and can serve as a trellis - sow a few pole-bean seeds in a ring around the corn.
• Squash last, about a week after the beans - a few seeds at the mound's edge, thinned to one, to run out across the ground between the hills.

Use pole beans and a running squash, not bush types - the whole structure depends on one climbing and one sprawling.

The honest limit worth knowing

The story that the beans feed the corn this season is the one everyone repeats, and it is overstated - most of a legume's nitrogen reaches its neighbours only after its roots and leaves break down, largely the following year. The beans improve the ground; they are not fertilising this year's corn. The companion planting, honestly guide has the full picture, and the Three Sisters guild page shows every claim graded. Grow it for the real structure - a living trellis, a living mulch, a block that pollinates - not for a nitrogen transfer that mostly isn't happening yet.