Author: Natalie Hoidal, UMN Extension educator, local foods and vegetable crops
Summer is here, and so begin weekly vegetable updates. In this series I'll provide an overview of things we're seeing in the field, a crop report, and issues to anticipate in the coming week.
If you're seeing interesting things in your fields, need help identifying problems, or just want to share photos, we'd love to hear from you! Growers can reach out directly to me any time at hoida016@umn.edu, and you can submit questions and diagnostic help here.
Vegetable weather report
Conditions have been very dry across the state this week, but rain is in the forecast for most of Minnesota starting next weekend. While Southern Minnesota and far Northwestern Minnesota have received substantially less rainfall than normal since April, the Northeastern part of the state and the areas around Alexandria have received substantially more rainfall than normal.
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| Map: Minnesota DNR, State Climatology Office |
However, in the last week or so conditions have been fairly dry throughout the state. The ongoing dry spell allowed growers an excellent window of planting time, and the warmer weather in the forecast is ideal for quick seedling growth.
The DNR publishes summaries of annual normal temperatures from 1981-2010, which they use to estimate last spring frost dates (less than 10% risk of 32 degree weather). For areas south of Willmar and Minneapolis the risk of frost has passed, but north of that line frost is still very much in the cards. Click on the link to see frost dates for your area. All of that said, temperatures are not expected to reach freezing in the next 7-10 days, even as far north as the Iron Range.
Soil temperatures are warming quickly across the state. The Minnesota Department of Agriculture publishes daily
updated soil temperatures for major field crop growing regions of the state.
Data is compiled from MDA managed stations in the Southern half of the state,
and NDAWN managed stations in the northern half. As such, the data is presented
slightly differently. The following tables provide a snapshot of soil
temperatures across the state. For more detailed info, see https://app.gisdata.mn.gov/mda-soiltemp/
Soil temperatures from MDA stations, data collected to 6’’ depth
|
Station location |
Nearest major town |
Coldest soil temperature in the last 7 days (approx.) |
Temperature on May 12, 2020 |
|
Blue Earth |
Albert Lea (Iowa border) |
50.5 º F |
52 º F |
|
Russel |
Marshall |
47 º F |
62 º F |
|
Henderson |
St. Peter / Belle Plaine |
49 º F |
61 º F |
|
Campbell |
Wahpeton / Elbow Lake |
49 º F |
56 º F |
Soil temperatures from ND-managed stations in MN
|
Station location |
Nearest major town |
Average turf soil temp on May 21 (4’’) |
|
Sabin |
Fargo / Moorhead |
55 º F |
|
Mavie |
Thief River Falls |
50 º F |
|
Fox |
Roseau (Canada border) |
50 º F |
Crop updates
- Cole crops: Most farmers have planted / transplanted their first couple of Brassica successions at this point. Our degree day models are forecasting adult cabbage maggot emergence in the very southern tip of Minnesota around May 13th, and seedcorn maggots are already flying in the southern half of the state. If you use row cover, now is a good time to start getting it ready if it's not already out, at least for growers in the southern half of the state.
- Sweet corn: Soil temperatures are reaching 55 degrees throughout the southern half of the state, meaning we're reaching the time of sweet corn planting! Some varieties do better with soil temperatures of 60-65, so check your seed packets before you get too enthusiastic about planting this week.
- Lettuce: Spring high tunnel lettuce is soon coming to an end to make way for warmer season crops, but all of the lettuce I saw this spring looked beautiful with no notable issues. Growers in southern Minnesota transplanted lettuce outdoors as long as a month ago, and growers in the northern part of the state are just getting started.
- Carrots and beets: Many farmers have planted their carrots and beets. Remember that these crops need *very* consistent moisture to germinate, so irrigate these fields daily (especially if your soil is prone to crusting), and consider adding row cover until emergence to hold moisture near the soil surface.
- Onions: Many growers have had their onions planted for a little while now; no reports of any issues yet!
- Garlic: Ideally, garlic would receive about 1/3 of its nitrogen requirements in the fall at planting, and the rest in early May. It's getting to be a bit late for nitrogen applications, as late nitrogen can delay bulb formation. However, if you haven't fertilized your garlic this spring do so asap. More info on garlic management.
- Asparagus: Asparagus harvest is well under way.
- Potatoes are mostly planted at this point, but there's still plenty time to plant if you haven't done so. Many growers took advantage of the dry weekend ~2 weeks ago when it was still too cold to plant other things to get their potatoes in the ground. We've been digging trenches around potato fields for Colorado Potato Beetle control before they emerge, and will have more data to share on the efficacy of trenches after this year. I received my first report of an adult CPB citing today (5/12/2021) near North Branch, MN!
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| A potato beetle trench, dug by hand. This was a 50'x50' field, and it took about 2.5 hours for 2 people to dig the trench, cut the plastic, and install it. You can also do this much more quickly with a tractor. Photo: Natalie Hoidal |
- Peas are establishing well, and most seem to have weathered the freeze just fine. We saw a lot of pea diseases last year. This spring is warmer and drier than last spring, but make sure you're rotating your planting location nonetheless. For growers who have had consistent pea disease issues, microbial inoculants containing Trichoderma spp. and Bacilus spp. often show disease suppression effects, though results are quite variable based on location, weather, soil conditions, etc.
- Peanuts?! I will not be posting weekly peanut updates, but we do have a small open field / low tunnel peanut trial going on in Marine on St. Croix. Despite being a tropical crop, studies from the early 80s in Minnesota show that an early May planting is likely to result in higher yields than later planting dates. So if you're planting peanuts, now is the time to do so - keep in mind that the inoculant for peanuts is a different species of rhizobium than the inoculant for peas, beans, vetch, etc., but it is widely available online.
- Tomatoes: Tomatoes are all over the place - some growers have had their tomatoes in high tunnels and greenhouses for a while and are already at the flowering stage; others are starting to transplant into tunnels this week. As you do so, keep a close eye out for bacterial diseases, and only plant healthy looking plants without spots. Bacterial spot can have variable symptoms, so be skeptical of any spots at this point to prevent the introduction of infected plants into your tunnel.
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| Planting peanuts, covered in inoculant. Photo: Natalie Hoidal |
Problems in the field
Potting mix issues
I've received a higher than normal inflow of questions about potting soil issues this spring. It seems that there's been an increased demand for potting soil (this is anecdotal), and suppliers are struggling to keep up. Some have changed their mixes, and in some cases farmers have had to buy from different suppliers. Why does this matter?
- I've received a few calls from growers whose plants are experiencing symptoms affiliated with high salt levels, including burnt leaf margins, and lesions along leaf veins that are not disease-related.
- I was also called about two distinct situations where growers received very hot (~130 degrees or so) compost. If your compost is this hot, it is likely not finished composting, and should not yet be used.
At this point in the season, there's not much to be done about these situations. However, if you suspect problems with your potting soil, it is worth getting it tested. The UMN Soil Lab has a $25 test for soil media under their Greenhouses, Florists, and Nurseries tab. This test can analyze pH, soluble salts, nitrate, ammonia, phosphorus, potassium, calcium, magnesium, sodium, iron, manganese, zinc, and boron.
Educational opportunities
The Vegetable Beet: join us during your lunch break
on Wednesdays for a 30 minute discussion about vegetables. Next week's
topic (May 19th, 11:30am) will be about mycorrhizal fungi and other microbial inoculants.
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