Upper Ground Sweet Potato Squash: The Complete Growing Guide for Zone 6b Kansas Gardens

Some varieties survive on flavor, some on toughness, and a rare few on history. Upper Ground Sweet Potato squash has all three. Thomas Jefferson documented this variety in 1790, calling it a potatoe-pumpkin when he sent seeds to a friend, and the gardens at Monticello still grow it today. It is an Appalachian Kentucky heirloom, a true Cucurbita moschata, and one of the least common heirloom squashes in circulation. If you garden in Kansas and you have lost squash to vine borers or August heat, this old Southern variety was built for exactly your problem.

What Is Upper Ground Sweet Potato Squash?

Upper Ground Sweet Potato (Cucurbita moschata) is an open-pollinated heirloom from the Appalachian region of Kentucky. The name describes the eating experience: tan skin over dense, sweet orange flesh that cooks and tastes remarkably like sweet potato, grown above ground on a vine. Fruits commonly run large, up to 20 pounds at full maturity, so one good fruit feeds a holiday table with plenty left for the freezer.

Because it is a moschata, it carries the thick, corky stems that squash vine borers rarely defeat. In Kansas, where borers reliably destroy Cucurbita pepo varieties by midsummer, that species difference is the line between a harvest and a compost pile.

Why It Excels in Zone 6b Kansas

Vine Borer Resistance

The squash vine borer (Melittia cucurbitae) targets soft, hollow pepo stems. Upper Ground's dense moschata stems are a poor target, and borers rarely complete their lifecycle on them. K-State's squash vine borer management guide (MF3309) recommends resistant species as the first line of defense, and this is that recommendation in seed form.

Heat and Drought Tolerance

This variety was selected in the South for hot, dry conditions. Once established, the deep-rooted vines handle central Kansas dry spells with less stress than most winter squash. Consistent water through fruit set still pays off in size and yield.

Storage

Like our other moschata varieties, properly cured fruits store 4 to 6 months in a cool, dry spot at 50 to 60 F. A September harvest keeps you in homegrown squash past Valentine's Day.

How to Grow It in Kansas

Starting Seeds

Direct sow after last frost, typically mid-April to early May in Zone 6b, once soil holds 65 F or warmer; 70 to 75 F is ideal. Plant 1 inch deep, 2 to 3 seeds per hill, and thin to the strongest plant. For a head start, sow indoors 3 to 4 weeks before transplant in 3 to 4 inch pots and harden off for a week before setting out.

Spacing

Plan for serious vines. Give each plant 8 to 10 feet of run, or train it up a strong trellis with fruit slings once squash begin to size up. This is not a patio container variety.

Soil and Feeding

Work 2 to 4 inches of compost into the bed before planting and target pH 6.0 to 6.8. Balanced fertilizer at planting, a nitrogen side-dress when vines begin to run, then a lower-nitrogen feed once flowering starts to support fruit set.

Days to Maturity and Harvest

Roughly 110 days. Harvest when the skin has hardened to its mature tan, the stem corks and browns, and your thumbnail no longer dents the rind. Cure in a warm, dry spot for 10 to 14 days before storage.

In the Kitchen

Treat it like the sweet potato it imitates: roast chunks until caramelized, mash it with butter, bake it into pies and quick breads, or cube it into curries and soups where the dense flesh holds together. The flavor is sweet and rich without being watery, which is exactly what you want for baking.

Saving Seed

Upper Ground Sweet Potato is open-pollinated and breeds true. Save seed from your best fully mature fruit, rinse, dry for 2 to 3 weeks, and store cool and dry; seeds stay viable 4 to 6 years. If you grow other moschata varieties nearby (butternut, Seminole, Long Island Cheese), isolate by distance or hand-pollinate and bag blossoms to keep the line pure.

Related Growing Guides

More vine borer resistant moschata varieties from our trial beds: the Seminole Pumpkin growing guide, the Dickinson Pumpkin growing guide, and the Waltham Butternut growing guide. For borer tactics beyond variety choice, read our complete squash vine borer prevention guide.

Get the Seeds

We have a very small first batch of Upper Ground Sweet Potato squash seeds: 10 packets of 10 seeds, open-pollinated and non-GMO, shipped from Newton, Kansas. When they are gone they are gone until we grow our own seed crop. Browse the full Vine Borer Resistant collection for the rest of the family.