Vegetable farming in the era of climate change

Climate Land Leader and farmer Dan Guenthner of Common Harvest Farm recently shared observations on climate change impacts over 35 years of vegetable farming. Following is a lightly edited version of Dan’s comments on the cohort call.

Dan Guenthner & Margaret Pennings of Common Harvest Farm near Osceola, WI

To place ourselves: We own 40 acres in the St. Croix River Valley, south of Osceola, WI. This is an alluvial outwash plain, so those farms within close proximity to the river valley have sandy and silty loam soil. This is very different than your Iowa loamy soils; we tend to have shallower topsoils and gravelly subsoils, and this factors into the water holding capacity of our soils. They’re fairly well suited for vegetables if you have irrigation, which we’ll talk about.

We have three vernal ponds, a small woodlands, a little bit of pasture, and we earn our living from 10 acres of organic vegetables. We’re not certified organic. We’ve been doing this for 35 years. We do almost all of our distribution through a CSA (Community Supported Agriculture). In addition to that, about 25% of what we raise goes to food shelves primarily in the Twin Cities. Our members support that effort by paying for some of the associated labor costs and transportation.

We’re very fortunate in that we have a very committed group of members, many of whom have been with us for many years. Our members tend to be very interested in climate issues. They do not shy away from having difficult discussions about climate impacts on the farm and want to know how it’s impacting us. That ends up creating an opportunity for dialogue, and we don’t feel alone. We know that we have a group of people who are really wanting to work through some of these challenges with us, and that makes our work easier.

We typically grow about 40 different types of vegetables; diversity is the key to a fresh market vegetable farm like ours. We are planting something almost every week – that’s one of the things that distinguishes us from the conventional row cropping system; we are continually planting.

Vegetables require about an inch of moisture a week. When we started farming, we did not have irrigation for the first five years. In the first 10 years that we farmed, the longest dry spell we had was three weeks. Often it would dry up in late summer, you’d have an August dry spell, and then the fall rains would return. By contrast, in 2023, we had 14 weeks of a very pronounced dry spell, coming on top of now a three-year pattern here of drier than normal precipitation.

So what are some of the impacts that we’re seeing on our farm?

Averages don’t tell the whole story

This past year is a good example: our driest year in 34 years of farming this past year, and yet at the end of the year, we ended up only about three inches below normal on precipitation. That largely had to do with a couple things. We had above normal snowfall last winter and no frost in the ground, so all of that moisture, about eight inches of liquid precipitation, went into the ground. We also had nine inches of precipitation within a six-week period in the fall. On Christmas Eve and Christmas Day we had 1.63 inches of rain, which exceeded the total we received in the months of May and June, historically our two wettest months of the year. So the averages really don’t tell the whole story.

Along with this is the uneven distribution of precipitation. I’ve heard it said by [meteorologist and climatologist] Mark Seeley that in 1970 about 70% of the precipitation fell in the form of a gentle shower and about 30% in the form of thunderstorms. Now that has flipped: we receive about three quarters of our precipitation in the form of a fast-moving thunderstorm, often with high winds and rain falling at a rate that the soil cannot absorb. When rain falls at a high rate, because we have silty loam soils, the rain tends to put a cap on the soil. This means when rain falls hard, it tends to compress the surface of the soil, and that leads to a good portion of that water running off and not making it into the soil profile. So if you look at the averages of precipitation and the distribution of precipitation, not all of it is making it into the root zone to the benefit of the plant.

So what are some patterns that we’re seeing?

Changing seasons and warmer nights

One of the things that has been observed over the last 10 years is cooler springs. We’re having these sluggish springs where we just can’t seem to warm up, and then we move very quickly to summer-like temperatures. In 2021, we had a frost on May 27th. That’s a late frost for us. Our average last frost is about May 5th. On June 3rd of that year, we had 90 degrees, and we had eight days in a row above 85. This is a week after we’ve had a frost. On that May 27th, we covered more than six acres with row cover because we had already had all of our sensitive plants out – peppers, eggplant, tomatoes. Plant shock from heat is also an issue. Young tender transplants cannot acclimate themselves quickly enough to be ready for the shock of those high temperatures.

Dan Guenthner (left) showing other Climate Land Leaders an example of what he calls a “climate weed”

One of the other trends that we’re seeing is warmer nighttime temperatures. On face value, you would think, wow, isn’t that generally a good thing? Unfortunately, what we’re talking about here is disrupting natural patterns, and even small disruptions can have really profound differences. One of the things that we’re seeing on our farm is accelerated weed growth. For example, a few years ago we had our crew out hoeing, trying to finish a field by the end of the day on Friday. Our crew doesn’t work on the weekends, so everybody was wrapping up the week and taking off, and we had six rows left to hoe in this field. By Monday morning the weeds had tripled in size because of these warm nights. Instead of cooling down into the upper 50s or around 60, it had held in the 70s, and the rate of growth was just astounding. In an organic cropping system, we’re relying upon mechanical means to control weeds. When something becomes rooted, our options become more limited in terms of the effectiveness of hoeing and what we’re capable of. We took an equal amount of time to eradicate the weeds in those six rows as we did in the field of 30 rows because of the growth we saw over the course of a weekend.

We’re seeing life cycles of insects changing. Insect cycles are based upon heat degrees, and historically they have followed these predictable intervals of hatching. Now those are getting kind of blurry. For example the flea beetle historically would come for about three weeks in the spring and then go through an eight-week egg-laying and incubation cycle before we had them again. Now that eight week period between those two hatches has been shortened to four or five weeks. With the Colorado potato beetle, historically we had a period without them; now we see larvae throughout the summer. Biological sprays are very expensive, and we are having to spray more often.

First frosts are later in the fall. Just in the past decade alone, the average first frost date in the fall has moved back about two weeks. And so you think, okay, well what’s wrong with having a nice extended fall? But we now have the life cycle of insects extended; there may be another complete hatch of certain insect populations. We’re having extended weed growth periods when weeds are still able to flower and set seed.

Winter is our friend. If you look at a map of organic matter in this country, the highest organic matter is in the northern latitudes. The reason for that is winter slows down the metabolic process in the soil. It’s basically giving all those soil organisms a chance to rest and slow down. Frost helps break up the soil. It helps break disease cycles. Winters are now shorter here. Places in southern Wisconsin now have four fewer weeks of winter temperatures than they did 25 years ago. These changes are accelerating other changes.

Summers are hotter. This past summer was a good example of having hotter summers and what that means for the varieties of crops that we’re growing. We experienced what is normally the average temperature for Kansas City or St. Louis, a location that’s historically two growing zones south of us. There again on face value it’s easy to say, well, what’s wrong with that? Can that really be all that challenging or difficult? For vegetable farmers what’s becoming increasingly difficult is growing cool season vegetables, things like spinach and fall brassicas and certain herbs. Spinach is a really important crop for us. It’s highly nutritious. It’s suited for a northern climate Fall. Spinach will not germinate in soils that exceed 80 degrees. We seed it in the middle or latter half of August. Now we have to use overhead irrigation to cool down the soils in order to get spinach to germinate. Then when we have these hot and extended falls – for example we had a record high temperature this past September – our spinach is reaching a smaller size and then showing signs of bolting in the fall, which is historically more of a problem for spring spinach. Spinach has been a staple for us. This is a crop that has been relatively easy to grow in the past that’s now becoming more difficult to grow.

Nagging questions and hopeful things

I’ll wrap up with some nagging questions. One of the nagging questions is, will we need to change some of what we’re growing? Is the variety of what we’re growing likely to change within our lifetimes? This is not a hypothetical thing. I can see in the not too distant future when certain things that we’re growing are going to become more difficult, and we’re going to have some hard decisions.

Another nagging question is, can we grow an entire crop on delivered water? I was born in Montana and grew up in Idaho. I grew up in a very arid climate. One of the things I love about living in the Midwest is it rains here. Irrigation for us on our scale is a very time-consuming enterprise. We have not only the moving of the pipe or setting the drip lines, but there are lots of repairs – gaskets and valves and problems with our pump. Big farms have a full-time irrigator. For a small farm like ours, when it doesn’t rain that means the equivalent of my getting another part-time job. So I may be working 70 hours a week, and all of a sudden I’m working an additional 15 to 20 hours a week just on irrigation. Most of the small vegetable farms don’t have a lot of excess water in terms of our capacity to deliver it or the source of pumping it, and if you’re pumping out of a well the water isn’t tempered, so you’re creating your own shock by delivering cold water to the vegetables.

A final nagging issue is, I think local food needs to be more expensive. We’re talking about some very real realities here. The premiums in organic food have largely disappeared in the last 30 years as we’ve had bigger and bigger players get involved in organic food. It has a way of capping and suppressing the locally produced food as well. And yet we’re shouldering more costs for refrigeration, irrigation, labor and other things. We have difficult working conditions working out in the heat and the [wildfire] smoke. So these are some of the big picture questions about a place, the upper Midwest, that historically has been a really wonderful place for growing vegetables.

I’ll end with a couple hopeful things. We have such a committed group of CSA members who want to talk about these challenges and who support the farm. They helped with a downpayment for our farm and the purchase of a conservation easement for it and paid for a solar array, which produces one hundred percent of our electrical needs.

Another hopeful thing is we’re taking more land out of production. As vegetable farmers we have some advantage because of the economics of high value crops. We can be better stewards of some of that marginal land in terms of getting it planted in perennial cover, woody vegetation and other things.

I’ll close by saying how much we’ve enjoyed connecting with the Climate Land Leaders. Being connected with all of you is a really hopeful thing. We’re all in this together. No matter what our enterprise or land or scale, we’re all going to have to figure out how to work together.