Fruit Trees for Watertown, Oconomowoc, Lake Mills, Jefferson and Fort Atkinson, Wisconsin

In the January 2019 cold snap, the Watertown and Fort Atkinson weather stations both bottomed out at −31°F. In the February 1996 cold snap the same two stations were 12°F apart: −27°F at Watertown, −39°F at Fort Atkinson. Some nights the cold fills the whole country; other nights it drains off the high ground and sits in the low spots. That's the thing to understand about fruit trees for Watertown, Oconomowoc, Lake Mills, Jefferson and Fort Atkinson. In this low, rolling corner of south central Wisconsin, the drumlins, the old lake beds and the Rock River bottoms each keep their own winter.

The map covers most of Jefferson County plus the edges of Dodge and Waukesha counties, from Watertown, Waterloo and the Oconomowoc end of Lake Country down to Fort Atkinson and the north shore of Lake Koshkonong. Type your address in the box on the map to get the number for your own place, and the list of what we sell that has come through it.

How to read this map

The big number at each spot is the 30-year planning low, the same number our cold hardiness calculator uses, built from NOAA station records with a small nudge for the ground around you. It leans cold, a safe number to plan around, not a record. The MFTC zone puts it in half zones. The typical winter is an average year's coldest night, the kind of average USDA's map uses. The spring layer shows how much warmer or colder a spot runs than Watertown on a still, clear night at bloom.

Watertown, the reference town, plans for −28°F (MFTC 4a), typical winter −15°F. The middle of the growing ground plans for −27°F, half of it between −28°F and −26°F. The warm end runs through the middle of Jefferson County, where Johnson Creek, Helenville, Hoopers Mill and Whispering Oaks plan for −25°F, just inside MFTC 4b. The cold end is the bottom of the Rock: Fort Atkinson and Blackhawk Island plan for −30°F. That's about 5°F of spread in winter, but about 10°F at bloom across named places, and that's where picking your spot pays.

Why the map looks the way it does

The glacier built this country. Jefferson County has more than 2,000 drumlins, streamlined hills 3 to 66 feet high, packed tight around Watertown and running north and south. Around them lie the beds of glacial Lake Scuppernong, flat lake plains covering about 38 percent of the county, with peat more than 6.5 feet thick common in the old basins (the state geological survey's 2022 county map). Most of those wetlands are drained and farmed now, but they're still the lowest, flattest ground around: the Jefferson Tamarack Swamp, Zeloski Marsh, Bean Lake below Rock Lake, the Crawfish bottoms. The Rock River gathers it all, coming through Watertown, taking in the Crawfish at Jefferson and the Bark at Fort Atkinson, and leaving through Lake Koshkonong, the lowest ground on the map at 774 feet.

On a still, clear night cold slides off every drumlin into the hollows and lake flats, then down the river lowlands. With hills this low the pools are shallow and patchy: a drumlin flank can work as a little thermal belt and the hollow below it as a little frost pocket. A 1936 Michigan State study found orchard ridges only 25 to 30 feet above the surrounding plain can be nearly as frost free as high hills, and that's the scale of relief here. The spring layer shows it. Hebron, on a 7 percent hillside 70 feet above its floor, reads 8°F warmer than Watertown at bloom. North Shore on Lake Koshkonong, right at the floor, reads 2°F colder, the coldest spring reading of any named place on the map.

The winter number takes that fine terrain at only a quarter strength, so in winter the stations drive the pattern, and their story is the Rock River bottom. The Fort Atkinson station sits at 787 feet, the town's own height and the lowest of the long-record stations, where the Bark comes into the Rock a few miles above Lake Koshkonong. It was the coldest station inside the map in the 1959, 1963, 1979 and 1996 cold snaps (in January 1979, −30°F against −22°F at Oconomowoc). Cold air runs to the lowest, flattest ground on a still night, and the Rock lowland from Jefferson to Koshkonong is just that, though we haven't found a local study that pins down why this station runs so cold. Other nights the gap closes: Fort Atkinson was among the mildest stations in the 1972 and 2009 cold snaps, and in 2019 nearly every station read −29°F to −31°F. Spreads open on still, clear nights and close when deep arctic air fills the whole region.

The lakes don't buy much winter. Lake Koshkonong is 10,460 acres but averages 6 feet deep, and shallow water freezes early and quits giving off heat. Rock Lake (60 feet at its deepest) and Lac La Belle (45 feet) can hold out longer, but lakes shelter their shores only while they're relatively free of ice, as the Wisconsin State Climatology Office puts it, and every station record on this map was set between January 30 and February 20. Lake Ripley, on the west edge, has frozen over in January only six times since 1989, and its latest ice-on on record was January 17, 2007, so most winters it's capped well before the worst nights. Over its long record the Lake Mills station has the same −17°F average yearly low and the same −33°F record as Watertown's.

Watertown, the Rock River bend and the drumlins

Watertown grew up inside a horseshoe bend of the Rock, where the river drops about 20 feet in two miles over two 10-foot dams. The town point, at 819 feet and 10 feet above its floor, plans for −28°F (MFTC 4a), typical winter −15°F. Within 3 miles the floor has a median of −27°F, and the warmest tenth of the ground plans for −25°F. There's hardly any ground 100 feet above the floor near town, so your warm ground is a drumlin flank.

The flanks south and southwest read warm at bloom. Ebenezer, about 4 miles south and 50 feet above its floor, plans for −26°F and reads 3°F warmer than Watertown in spring; Grellton, 5 miles southwest and 60 feet up, plans for −26°F and reads 7°F warmer. Pipersville, on a 6 percent slope toward Ixonia, plans for −26°F and reads 4°F warmer. Hubbleton, on river-bottom ground 8 miles west, plans for −28°F and reads 2°F colder. Put a Contender peach (−30°F) or a Westcot apricot (−45°F) on a Grellton kind of flank, and keep the bottoms for apples like Haralson (−45°F) and bush fruit.

Oconomowoc, Lac La Belle, Pabst Farms and Summit

Oconomowoc is the hub of the western Lake Country: Fowler Lake downtown, about 97 acres and 50 feet deep; Lac La Belle to the northwest, 1,186 acres but averaging 11 feet deep; Oconomowoc Lake to the east, ringed by the village of the same name. The city's town point, on river-bottom ground at 864 feet, plans for −28°F (MFTC 4a), typical winter −14°F, and its spring reading matches Watertown's. Lac La Belle village, by the lake at 856 feet, also plans for −28°F and reads 1°F colder at bloom. Climb a little and it changes: the hamlet of Lake Lac La Belle, 50 feet above its floor, plans for −25°F, 3°F milder than the village a mile away. Oconomowoc Lake village plans for −28°F but reads 3°F warmer than Watertown at bloom. Prairie Creek Ridge, 2 miles northeast of downtown, plans for −27°F, and up north Ashippun and Old Ashippun −29°F.

South of the city the ground runs higher. Pabst Farms, the Pabst family's old farm, came into Oconomowoc from the Town of Summit in 2003. It sits at 892 feet and plans for −25°F, like the Town Centre at Pabst Farms and Summit village: 3°F milder than downtown Oconomowoc, under 4 miles away. The Ponds at Pabst Farms, on lower ground a mile north, plans for −27°F, and Dousman −27°F. At −25°F, Lapins sweet cherry (−35°F), Superior plum (−35°F) and Blushingstar peach (−30°F) all have room. East of Oconomowoc Lake, our Milwaukee, Waukesha and Racine map picks up.

Lake Mills, Rock Lake, Aztalan and Waterloo

Lake Mills sits on the east shore of Rock Lake, a 1,365-acre figure eight, and gives its name to the hummocky moraine highlands of the area. The town point, at 833 feet and 10 feet above its floor, plans for −25°F (MFTC 4a), typical winter −13°F, and reads 1°F colder than Watertown at bloom. Within 3 miles the floor runs −26°F and the slope ground 100 feet and more above it −23°F, among the warmest slope numbers on the map. Hoopers Mill, 2 miles east on river-bottom ground, plans for −25°F, just inside 4b, but reads 2°F colder at bloom.

Aztalan, about 3 miles east of Rock Lake on the Crawfish River, is where a Mississippian town stood from about A.D. 900 into the 1200s or 1300s, its people growing maize and gathering acorns, hickory nuts and berries. The hamlet sits 50 feet above its floor, plans for −25°F and reads 5°F warmer than Watertown at bloom, the best spring reading of any named place near Lake Mills. That's apricot and pear ground: Harlayne apricot (−30°F), Seckel pear (−35°F).

Waterloo, in the northwest corner of Jefferson County on river-bottom ground at 814 feet, plans for −27°F (MFTC 4a), typical winter −12°F, and reads 1°F colder than Watertown at bloom. Its station has only 14 years on file, and its 30-year number, −27°F, is colder than anything it has recorded (−26°F in 2019). On the west edge, Lake Ripley by Cambridge plans for −27°F. Cambridge itself is on our Madison and Yahara lakes map.

Jefferson, Johnson Creek and the Crawfish confluence

Jefferson, the county seat, sits where the Crawfish River joins the Rock just above I-94, at about 800 feet. Both rivers flood the land beside them every year (in 2008 they briefly closed lanes of I-94). The town point, on a 6 percent toe slope at 805 feet, plans for −25°F (MFTC 4a), typical winter −13°F, and reads 2°F warmer than Watertown at bloom. The slope ground 100 feet and more above the floor within 3 miles plans for −22°F, the warmest slope number of any town on the map. Whispering Oaks, a mile southwest of downtown, plans for −25°F, just inside MFTC 4b. Stable Rock Winery here makes apple, cherry and raspberry wines, and the state winery association files Jefferson under its Glacial Hills Region.

Johnson Creek, at WI 26 and I-94, grew where the railroad crosses the creek just above its mouth on the Rock. The village point, on a 5 percent toe slope 20 feet above its floor, plans for −25°F, inside 4b and the warmest number of any named place on the map, and reads 2°F warmer than Watertown at bloom. Farmington, 5 miles east and 40 feet above its floor, plans for −26°F and reads 3°F warmer.

Fort Atkinson, the Bark River and Lake Koshkonong's north shore

Fort Atkinson sits where the Bark River comes into the Rock, and it's the lowest town on the map and the coldest. The town point, at 788 feet and 10 feet above its floor, plans for −30°F (MFTC 4a), typical winter −16°F, and reads 1°F colder than Watertown at bloom. Within 3 miles the floor runs −29°F, but the slope ground 100 feet and more above it plans for −24°F, the biggest floor-to-slope gap of any town on the map. Old Lake Scuppernong left a delta near town at about 860 feet, some 70 feet above the river; get up onto ground like that and you're out of the bottom, headed toward that slope number.

Below town the Rock spreads into Lake Koshkonong, a deep-water marsh of reeds and wild rice until the Indianford Dam was built in 1932. The shore flats are cold ground at bloom: North Shore, Blackhawk Island and Lake Koshkonong read 2°F colder than Watertown. But Glenn Oaks Beach, on a 16 percent slope 40 feet above the floor, reads 7°F warmer, and Vinnie Ha Ha, 40 feet up a mile and a half from Blackhawk Island, 6°F warmer. In winter those bluffs still plan cold (−28°F at Glenn Oaks Beach, −29°F at Vinnie Ha Ha), because the winter number leans on the Fort Atkinson station. Hebron, 7 miles east of town, has the best spring reading of any named place on the map: on a hillside 70 feet above the floor, where cold air drains past, it reads 8°F warmer than Watertown and plans for −26°F.

So in Fort Atkinson, plant for the river-bottom number in town and save early bloomers like Siberian C peach (−35°F) and Debbie's Gold apricot (−45°F) for bluffs and hillsides like these. Around the lake and down the Rock, our Janesville and Beloit map takes over; it overlaps this one along the Koshkonong shore.

Sullivan, Helenville and the Glacial Drumlin Trail

The Glacial Drumlin State Trail, named for the drumlins along it, strings together Lake Mills, Jefferson, Helenville, Sullivan and Dousman. Sullivan, once Winfield, sits at 864 feet on the valley floor, plans for −28°F (MFTC 4a) and reads 2°F warmer than Watertown at bloom; Rome, 3 miles southwest, also plans for −28°F. Oak Hill, about 5 miles south of Sullivan at 819 feet, plans for −29°F and has the coldest typical winter of any named place on the map, −17°F. Helenville, toward Jefferson, plans for −25°F, just inside 4b; Jelli's Farm there runs u-pick apples. The National Weather Service's Milwaukee/Sullivan office keeps a station 3 miles southeast of the village at 929 feet, the highest on the map, and it gets the latest spring frost of any station here.

Spring frost and bloom in the drumlin country

More than nine in ten of the plants we sell are rated −30°F or colder, and 95 percent of the growing ground here plans warmer than −30°F. For most of the list, bloom nights decide things, not winter. Open blossoms of nearly every tree fruit start dying around 28°F (Michigan State's numbers), and NC State's fruit people say 3°F to 4°F can separate no crop from a full one. On a spring frost night the cold layer usually tops out 30 to 200 feet above the ground (the FAO's frost protection manual), so with drumlins no more than 66 feet tall, even partway up one counts.

NOAA station records for 1991 to 2020 put the median last 32°F in late April at the river-town stations: April 27 at Jefferson (only 15 years of data), April 28 at Watertown, Lake Mills and Fort Atkinson, April 30 at Oconomowoc. The Weather Service station southeast of Sullivan runs later, May 4. The last 28°F comes about two weeks earlier. One spring in ten the last 32°F comes as late as May 14 at Watertown and May 21 at Fort Atkinson and Oconomowoc; Fort Atkinson's median matches Watertown's, but its late tail runs a week behind. The frost free season runs 175 days at Jefferson, 166 at Watertown, 160 at Fort Atkinson and Oconomowoc and 158 at the Sullivan station. Lake Michigan usually holds southeast Wisconsin's bloom back, which gave it some protection in the 2026 frosts (Wisconsin Public Radio), but how far inland that reaches we haven't found measured.

Site first. Apricots, peaches, sweet cherries and pears go on the ground that reads warmest at bloom: drumlin flanks and bluffs like Hebron, Grellton and Glenn Oaks Beach, and higher villages like Oconomowoc Lake. The lake flats, peat and river bottoms are for apples, honeyberries and bush fruit. Only about 15 percent of apple blossoms need to set for a crop (University of Minnesota), and our Red Lake and Montana Black currants fruited well at our place in 2026 after their flower buds saw about 22°F. Unless the fruit is clustered, like cherries and grapes, most fruit can lose half its blossoms and you'd never know it. A hedge or tree line across the bottom of a slope backs cold air up into the trees above it, so open a gap at the low end. Through bloom keep the grass under 2 inches, don't till, and water a day or two before a frost night.

Fall counts too. The first fall 32°F comes from October 6 at the Sullivan station to October 17 at Jefferson, and a hard freeze before trees harden off kills at temperatures a January tree shrugs off. This is MFTC zone 4 country, so taper the water from mid-August, skip late nitrogen and don't prune in late fall.

What the weather records say

NOAA station records here go back to 1893. The coldest readings on file: −39°F at Fort Atkinson (February 3, 1996); −33°F at Watertown (February 20, 1929); −33°F at Lake Mills and Oconomowoc (January 30, 1951); −30°F at the Sullivan station and Jefferson (January 31, 2019). Just past the edges, Whitewater read −37°F on January 30, 1951, and Hartford −35°F in 1979 and 1982; Hartford is on our Fond du Lac, West Bend and Kettle Moraine map.

The planning number is a planning number, not a floor. In the January 2019 cold snap six of the seven stations on this map reached or beat their own 30-year numbers, Jefferson's by 4°F, and Fort Atkinson's −39°F in 1996 ran 8°F past its own. That's why we rate every plant by the coldest it has actually come through, and why room to spare is cheap insurance. And the two stations behind the warm middle of the map never saw its worst night: Jefferson's started in 2005, and Lake Mills' has no readings on file for the February 1996 cold snap.

USDA's 2023 map moved most of inland southeast Wisconsin from 5a to 5b (−15°F to −10°F), and UW Extension says 5b now reaches west to Madison. The 1990 map had Watertown, Jefferson and Oconomowoc in 5a and Lake Mills and Fort Atkinson in 4b. USDA's zones come from an average winter, and our typical winters here (−12°F to −17°F) land near that 5a and 5b line; our MFTC zones, 4a and 4b, come from the bad night.

What you can grow here

The pollination maps show which trees pollenize which; Toka plum (−45°F), for one, is a good pollenizer for Superior.

The warm middle and the slopes: −22°F to −26°F

Johnson Creek, Helenville, Whispering Oaks and Hoopers Mill (−25°F, 4b); Jefferson, Lake Mills, Summit, Pabst Farms and Aztalan (−25°F, 4a); Hebron, Ixonia, Ebenezer, Grellton and Farmington (−26°F); the slopes near Jefferson, Lake Mills and Fort Atkinson (−22°F to −24°F). Anything rated −30°F or colder is a good pick: Honeycrisp (−45°F), Zestar!® (−40°F) and Northern Spy (−30°F) apples; Superior and Stanley (−30°F) plums; Lapins and Gold sweet cherries (−35°F); Seckel and Harrow Sweet (−30°F) pears on good-spring ground; Contender and Blushingstar peaches and Tomcot apricot (all −30°F) on the highest flanks; Marquette grape (−35°F). Plants rated −25°F, like Stella sweet cherry and Redstar peach, fit the 4b ground and the slopes and are worth a try in a good spot elsewhere in this band; just remember Jefferson's station saw −30°F in 2019.

Most of the map: −27°F to −28°F

Watertown, Oconomowoc, Lac La Belle, Oconomowoc Lake, Waterloo, Sullivan, Dousman, Lake Ripley and most of the Koshkonong shore. Good picks run from −30°F down: Haralson (−45°F), Honeycrisp and Freedom (−35°F) apples; Ure (−45°F) and Flemish Beauty (−40°F) pears, kept off the low ground; Toka and Alderman (−40°F) plums; Evans Bali (−45°F) and Meteor (−40°F) tart cherries; Siberian C peach (−35°F) for the most margin, Contender and Blushingstar (−30°F) and Sungold apricot (−40°F), all on flanks that read warm at bloom. Tom McCamant grows Contender at Forbidden Fruit Orchard in Paradise, Montana, and it's the only commercial peach we know of that has taken −32°F. The −25°F plants are only worth a try here, on your best spot.

Fort Atkinson, the Koshkonong flats and the Ashippun corner: −29°F to −30°F

Fort Atkinson and Blackhawk Island (−30°F); Vinnie Ha Ha, Oak Hill, Ashippun and Carcajou (−29°F). Plants rated −30°F just clear here, so lean on the ones with room: Kerr (−50°F) and Trailman (−55°F) applecrabs (if you only plant one tree, make it one of these), Wealthy (−50°F), Haralson and Honeycrisp apples; Summercrisp pear (−45°F), on the bluffs only; Brookred (−50°F) and Mount Royal (−45°F) plums; Evans Bali tart cherry; Siberian C peach and Debbie's Gold apricot on the bluffs at Glenn Oaks Beach and Vinnie Ha Ha. On the flats, bush fruit: honeyberries (−50°F), Consort black currant (−50°F), Montana Black Currant (−50°F; we've never seen winter damage on it), Pixwell gooseberry (−40°F) and Boyne raspberry (−50°F).

Roots, soil and site

Roots are the weak link, and snow protects them. At Ed Schultz's farm in Gallatin Gateway, Montana, Bud 118 apple rootstock has seen near −50°F under snow with no rootstock damage. After Wisconsin's snowless 2024 to 2025 winter UW's fruit program found apple damage "just below the graft union," so on bare ground hold the snow, mulch and go into winter with moist soil. Plant on a slope, off the floor and off a windswept top; Montana State recommends a 4 to 8 percent grade where cold air won't settle. The old lake beds are silts and clays and the basins hold peat, so test drainage first: dig 2 feet, fill it, let it drain, fill it again, and under 10 hours means well drained. Stay out of the Rock and Crawfish bottoms that flood every year. UW Extension's fruit pages cover fire blight, apple scab, codling moth, apple maggot and plum curculio.

Questions people ask

What zone is Watertown, WI?

Our map plans for −28°F in Watertown, MFTC zone 4a, with a typical winter of −15°F. USDA's 2023 map moved most of inland southeast Wisconsin from 5a to 5b, and UW Extension says 5b now reaches west to Madison. USDA's zone is based on an average winter, ours on the bad night we plan for.

When is the last frost in Oconomowoc?

At the Oconomowoc station the median last 32°F is April 30 and the median last 28°F April 17 (NOAA station records, 1991 to 2020). One year in ten the last 32°F comes as late as May 21. The first fall 32°F comes around October 10, for a 160-day frost free season.

Why is Fort Atkinson so cold?

We haven't found a study that explains it, but it's the lowest town on the map, where the Bark meets the Rock above Lake Koshkonong, and on still nights cold air drains to the lowest, flattest ground. Its station hit −39°F on February 3, 1996; in that cold snap Watertown's bottomed out at −27°F. Our map plans for −30°F in town but −24°F on the slope ground within 3 miles.

Can you grow peaches in Lake Country, Wisconsin?

Yes, on the right ground. Contender and Blushingstar (−30°F) clear Oconomowoc's −28°F, and Siberian C (−35°F) gives more margin. Peaches bloom early, so put them where the map reads warm at bloom, like Oconomowoc Lake (3°F warmer than Watertown) or a drumlin flank, not the river bottoms.

Where are the frost pockets in Jefferson County?

By the physics, the low ground: the old lake beds and peat flats (the Jefferson Tamarack Swamp, Zeloski Marsh, the Crawfish bottoms), the hollows between drumlins, and the Rock River bottom from Jefferson down to Lake Koshkonong. On the map, at bloom North Shore, Hubbleton, Blackhawk Island and Hoopers Mill read 2°F colder than Watertown, while drumlin flanks like Hebron and Grellton read 7°F to 8°F warmer.

What fruit trees grow in Jefferson County, Wisconsin?

Almost everything we rate −30°F or colder: Honeycrisp and Haralson apples, Superior and Toka plums, Lapins and Evans Bali cherries, Contender peach, hardy apricots, currants, honeyberries and grapes like Marquette. The map plans for −25°F around Jefferson, Lake Mills and Johnson Creek and −30°F at Fort Atkinson, so check your address, and let the spring reading decide where the early bloomers go.

Warmer spots, colder spots

Here's the number to plan for at named places on the map, warmest first. Each one is the 1-in-30-year low for that spot: the cold hardiness calculator's number from the same weather stations, sharpened by our microclimate model for the ground right there. Zone is our MFTC zone, set by that one bad night, not by an average.

The weather stations behind it

These are the long-record stations in and around this map, with each one's own numbers since the winter of 1995-96. The last column is this map's 30-year number right at the station, which won't match the station exactly: it's a blend of the stations around it, the way the calculator works everywhere.

Source: NOAA records through ACIS, winters 1995-96 through 2025-26. What the "carried forward," "gaps filled" and AWOS rows mean is explained in how our microclimate maps work.