Gardening in South Dakota: zones, frost dates and when to plant

East River, West River and the Black Hills

South Dakota gardeners talk about the state in halves, and for soil the split is real. East of the Missouri River, undisturbed soils built up deep organic matter under native prairie over thousands of years and are naturally productive, according to SDSU Extension’s Fertilizing Gardens in South Dakota. Most garden soils in the state sit near neutral, but West River soils can run strongly alkaline, high enough that some vegetables struggle.

Season length is the other dividing line. SDSU Extension’s Choosing Vegetable Varieties for South Dakota points out that in the upper Black Hills and across the northern part of the state, a variety needing around 120 days will not have time to mature. Gardeners in those areas, and anywhere elevation changes quickly, should lean on local experience along with the frost dates for your city above.

What limits gardens here

Moisture. SDSU Extension’s Vegetable Gardening in South Dakota calls water a frequent limiting factor. Vegetables need roughly 1 to 1½ inches a week from rain or irrigation, and a hot summer day can pull about a quarter inch of moisture out of the soil. Water deeply enough to wet the top 8 to 12 inches, then let the top inch dry before watering again.

Wind. Dry wind raises water loss and batters transplants. The guide suggests windbreaks of snow fence, a few rows of sweet corn, millet or sunflowers, or a row or two of Sudan grass on the windward side. Keep full-grown trees at least 50 feet from the garden, since their roots compete for water and nutrients. In windy spots, shorter-growing varieties hold up better.

Alkaline soil and free lime. Elemental sulfur can lower pH, but SDSU Extension notes that many South Dakota soils carry free lime (calcium carbonate), which makes acidifying impractical except in very small areas. Clay soils resist change too. Do not add lime or wood ash unless a soil test shows a need.

Salty water. Artesian water and some private wells are high in salts or sodium. Irrigating with them can build up salt in the garden, and high sodium damages soil structure. Have questionable water tested before relying on it.

Uneven spring weather. Swings between cool and hot spells in spring make cauliflower tricky, and cold nights make celery bitter and prone to bolting. SDSU Extension suggests celery only for dedicated gardeners in the warmer parts of the state.

SDSU Extension’s planting advice

Vegetable Gardening in South Dakota sorts crops by soil temperature. Spinach, peas, radishes, head lettuce and cauliflower go in during April or early May and fade in heat. Broccoli, cabbage, onions, carrots, beets, chard, potatoes and kohlrabi can go in at the same time or shortly after and tolerate more heat. Warm-season crops such as beans, sweet corn, squash, cucumbers, melons, tomatoes and peppers need warm soil and are damaged by frost.

Other points from the guide:

• Till in fall when you can. Snowmelt and spring rain often keep soil too wet to work on time.
• Clear plastic warms small areas quickly in spring. Hold off on organic mulch until the soil has warmed, then wet it down so it does not blow away.
• Hotcaps, row covers and wall-of-water devices let you set out transplants earlier and give some wind protection. Anchor them well.
• A fall garden goes in from late June through August, timed by each crop’s days to maturity. Make sure water is available, since these crops start in hot, dry weather.

Varieties that fit South Dakota

SDSU Extension’s variety guide gives state-specific direction:

• Cool-season crops: look for “heat-tolerant” or “widely adapted” broccoli, cauliflower and lettuce. Skip crisphead lettuce, which needs long, cool summers, and avoid broccoli sold as performing well in the Northeast.
• Asparagus: hardy all-male hybrids such as ‘Jersey Giant’, ‘Jersey King’, ‘Jersey Supreme’ and ‘Guelph Millennium’. Avoid California releases like ‘UC 157’, which are not hardy enough.
• Garlic: plant in late fall, one to two weeks after the first killing frost, under 3 to 4 inches of mulch. Hardneck types generally survive cold winters better than softneck.
• Onions: choose long-day or day-neutral types.
• Heirlooms: pick ones with a track record in the upper Great Plains.
• Cooler areas: check days to maturity for pumpkins, and choose shorter-season watermelons and early tomatoes.

Test the soil first

SDSU no longer offers commercial soil testing, but SDSU Extension lists neighboring university and private labs that do. For a sample, take slices about 6 inches deep from ten spots, mix them, and send about two cups. Most South Dakota gardens have enough potassium but need nitrogen, and sometimes phosphorus. A test tells you how much before you buy fertilizer.