Calabaza de Castilla: The Complete Growing Guide for Zone 6b Kansas Gardens
By Autumn Prairie Pumpkins
Calabaza de Castilla is the squash you see stacked at Mexican markets every October: big, deeply ribbed, light brown at maturity, heavy as a sack of feed. It is a Cucurbita moschata, the same species as butternut and Seminole, and it is one of the oldest domesticated squash on earth. Archaeologists have pulled moschata remains roughly 7,000 years old from caves in Tamaulipas and Puebla.
The name is a piece of colonial confusion. Spaniards carried the squash from the Americas back to Europe, and Europe assumed anything that good must have come from Castile. It never saw Spain until after it was already ancient in Mexico.
It grows well in Kansas. It also takes over. Here is what to expect.
The specs
- Species: Cucurbita moschata, open-pollinated heirloom
- Days to maturity: 100 to 110 days from direct sowing
- Days to germination: 7 to 10 days in warm soil
- Fruit: light brown rind, deep ridges, rich orange flesh, averaging 15 to 20 pounds
- Vines: very vigorous, reported as long as 50 feet
- Spacing: hills 4 to 8 feet apart
- Seed depth: 1 inch, in a mound 3 to 4 inches tall and about a foot wide
- Soil: fertile, well drained, slightly acidic at pH 6.0 to 6.5
- Sun: full, all day
- Storage: 4 to 6 months at 50 to 60°F after curing
When to plant in Zone 6b
Do not rush this one. Moschata squash sulk in cold ground, and a seed that sits wet at 60°F will rot before it sprouts. Wait for soil at a steady 70°F at 2 inches deep. In south central Kansas that usually lands between May 10 and May 25.
Direct sowing beats transplanting here. Squash roots resent disturbance, and a direct-sown seed catches up to a transplant within three weeks. If you must start inside, use 4 inch pots, sow no more than two weeks before your transplant date, and set them out before the second true leaf hardens.
At 100 to 110 days, the latest safe sowing in Zone 6b is about June 13. Later than that and you are betting the harvest on a late first frost.
Soil and site
This is a heavy feeder carrying 15 to 20 pound fruit. Work 2 to 3 inches of finished compost into each hill before planting, or a shovelful of aged manure worked in the fall before. Skip fresh manure in spring, which pushes vine at the expense of fruit.
Drainage matters more than fertility. A hill 3 to 4 inches tall does two jobs: it warms faster in May and it sheds water in a Kansas gully washer, which keeps crown rot off the plant.
Spacing, and the 50 foot problem
The seed house reports runners up to 50 feet. Plan for it rather than fighting it.
- Hills: 4 to 8 feet apart in every direction, 2 to 3 plants per hill after thinning. Go to the wide end of that range if your soil is rich.
- Row style: plants 3 feet apart in the row, rows 8 to 10 feet apart
- Edges: plant along a fence line, a field edge or the back of the garden and let the vine run out into ground you were not using. It will smother weeds while it goes.
Trellising is not practical here. A 15 to 20 pound fruit needs a sling and a cattle panel rated for real weight, and the plant is happier on the ground where it can root at the nodes. Those secondary roots are worth having in August.
Water and feeding
An inch a week, delivered at the base, is the target. Drip or a soaker hose beats overhead watering by a wide margin, because wet leaves at dusk are how powdery mildew gets started.
Water deeply and less often rather than a daily sprinkle. Deep water pulls roots down where the soil stays cool in a Kansas July. Side dress once when the vines start to run, and again when the first fruit sets to the size of a softball.
Expect the big leaves to wilt at 2 p.m. in August heat. If they are upright again by evening, the plant is fine. If they are still flat at dawn, check for borers.
Pests: borers, bugs, mildew
Squash vine borer. This is where moschata earns its keep. Borers lay on the stem base, and the larva tunnels through soft, hollow pith. Moschata stems are dense and solid, so the larva often fails to establish. This is resistance, not immunity. The best insurance is free: bury two or three leaf nodes along the runner with a scoop of soil in early July. Each one roots and becomes a backup plant if the crown is hit. Kansas State's guide MF3309 covers timing and trap crops in detail.
Squash bugs. Check the undersides of leaves twice a week from late June. Scrape the bronze egg clusters off with a putty knife or a strip of duct tape before they hatch. A board laid flat near the crown at night collects adults you can dispatch at dawn.
Powdery mildew. Almost inevitable by late August in Kansas humidity. It usually arrives after fruit set and costs you little. Space for airflow, water at the base, and do not panic when the older leaves go silver.
Harvest and curing
Harvest when the rind has turned light brown and dulled from glossy to matte, and a thumbnail will not dent it. The stem should be dry and corky. Cut, do not pull, and leave 2 to 3 inches of stem on the fruit. A squash without its stem is a squash with an open wound.
Cure for 7 to 10 days somewhere warm, 80 to 85°F, out of the rain. A few days in direct sun on a pallet works, so does a closed truck bed or a sunny porch. Curing heals small scrapes and converts starch toward sugar, which is why a cured squash tastes better in December than it did in September.
Storage
Cured moschata squash hold 4 to 6 months at 50 to 60°F with moderate humidity. A spare bedroom closet, a stair landing or an unheated back room is usually about right. Do not refrigerate, and do not let it freeze. Set fruit on a shelf without touching, stems up, and check monthly for soft spots.
In the kitchen
The traditional use is calabaza en tacha: chunks of squash simmered slowly with piloncillo, cinnamon and orange until the flesh candies and takes on a dark syrup. It is a Day of the Dead staple and the reason this variety is grown by the truckload in Mexico.
Beyond that it behaves like any good pie squash. Roast it, puree it, fold it into empanadas or a pie, or cube it into a pot of beans. The seeds are large and plentiful and roast into proper pepitas, which matters when a single fruit carries a few hundred.
Saving seed
This is an open-pollinated heirloom, so seed saved from your best fruit will grow true. The catch is that Cucurbita moschata crosses freely with every other moschata in bee range, which includes butternut, Seminole and most of the tan pumpkins. If you grow only one moschata, save away. If you grow several, hand pollinate and tape the flower, or accept that next year's fruit will be a surprise.
Scoop, rinse the pulp off, dry on a screen for two weeks somewhere with moving air, and store cool and dark. Squash seed stays viable 4 to 6 years, with the strongest germination in the first 2 to 3.
