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Weekly vegetable update 5/18/2022

Author: Natalie Hoidal, UMN Extension educator, local foods and vegetable crops

This was a rough week. Many of you sustained damage to your farms, including damage to high tunnels and other infrastructure, as well as damaged trees. Heavy rains delayed planting and bed prep yet again, and the cooler weather sustained many of the issues we've been having with humidity in greenhouses. Looking forward, the week ahead looks more calm, though temperatures will remain cool.

Crop updates 

Crops continue to be delayed due to cool weather and wet fields.  
  • Sweet corn: Growers in Southern MN can probably begin direct seeding sweet corn this week, especially if you have varieties suited to cooler soils. Transplanted corn seems to be doing well so far. The seedcorn maggot forecast predicts that the first generation has emerged already in the southern half of the state. Read more about it here.   
  • Asparagus: Asparagus harvest is now underway, and asparagus beetles are laying eggs. Eggs are black and usually stick out at a 90 degree angle; they can be along the stem or in the top of the spear. Harvesting spears regularly can help reduce populations since doing so removes eggs from the field. The threshold for spraying is: 1/10 plants have adult beetles, 50-75% of the plants have larvae, or 2% of spears have eggs. Learn more about management options in the Growing Asparagus in Minnesota guide.

Asparagus beetle eggs. Photos: Annie Klodd

  • Cole crops: Most people have finally been able to get their Brassicas out into the field. The cabbage maggot forecast shows that adults are already flying in the Southern part of the state, and they should reach central Minnesota this week. I've already seen some flea beetles in Dakota County. Consistent cool weather increases the likelihood of bolting when warm weather finally comes. Brassicas are winter annuals in their home range of the Mediterranean, and they have to go through a vernalization period to trigger flowering. Our cold spring evenings provide this vernalization, and once they are exposed to enough cold, they can enter their reproductive / flowering phase. One of my broccolini varieties at home has already bolted! 

Bolting broccoli. Image: ret0dd, Wikimedia

  • Tomatoes and peppers: Our return to cool weather and plenty of moisture in the atmosphere this week means growers need to be extra vigilant about increasing airflow in greenhouses / tunnels, and scouting for disease. We've seen plenty of gray mold and bacterial leaf spot already this spring. 
  • Garlic: Garlic is catching up quickly, despite a slightly delayed spring. In this month's Premium Garlic Newsletter, Jerry Ford shared some preliminary results from garlic demonstration plots at six farms across the state (full results to be published soon). Here's what they found regarding spring mulch removal:

    It’s an abiding practice among some garlic growers to remove mulch in the spring to warm up the ground and give the plants a head start.  Other growers claim that it doesn’t make a difference, and the reduction in weeding by leaving the mulch on is worth it.  In 2018, we had six farms participating, and in 2019 there were five.

    We found that it made little difference in the size of the bulbs harvested. In 2018, the un-mulched bulbs were an average of 9% smaller than those where the mulch was left in place; whereas, in 2019, they were 3.4% larger.  All the growers reported that they had to weed the un-mulched plots more often.  One farm claimed that un-mulched bulbs were harder to clean.
  • Carrots and beets: Many growers may have to re-plant after the heavy rains last week. Keep an eye on your soil to prevent crusting, which can happen after heavy rainfall events. Providing light irrigation to keep the top half centimeter of soil consistently moist can help to prevent crusting in fields where you're waiting for small seeded crops to germinate.  

Vegetable weather report

With warmer weather coming in to Minnesota today and tomorrow, meteorologists are predicting scattered thunderstorms throughout the state with the possibility for more severe weather on Thursday. 
After the storms pass, we'll continue to see cool weather for the next week or so, with lighter rain in 5-7 days. Most of the state can expect around an inch of rain this week, with more like half an inch in West Central Minnesota.
Soil temperatures continue to warm, but in most areas, we're not quite ready for planting warmer season crops (ideal soil temperature is around 65 for sweet corn, green beans, etc). 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

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 17, 2020 (approx).

Blue Earth

Albert Lea (Iowa border)

56 º F

61 º F



58 º F

68 º F


St. Peter / Belle Plaine

58 º F

62 º F



48 º F

51 º F

Soil temperatures from ND-managed stations in MN

Station location

Nearest major town

Approximate turf soil temp on May 17  (4’’)


Fargo / Moorhead

54 º F


Thief River Falls

50 º F


Roseau (Canada border)

50 º F

Problems in the field

Tunnel trouble

The storms last week resulted in significant damage to high tunnels across the state. I talked to a lot of farmers this winter who were enthusiastic about the benefits of using caterpillar tunnels vs. full-scale high tunnels, but many people saw the downside of smaller tunnels this week, which generally seemed to sustain more damage from heavy winds. Thankfully most people did not sustain major plant damage in their tunnels. Take some time to assess how your farm infrastructure held up in this storm, and how you can be more resilient going forward. Maybe that means moving your smaller tunnels to a more protected spot, or investing in windbreaks

Tunnel damage after storms. Photo credit: Ted Carey, Kansas State University via eOrganic.

Think twice about fertility as you prep your fields

I've been in a rabbit hole this winter exploring the significance of high phosphorus levels on vegetable farms. I often see soil tests from farms I visit where the phosphorus levels are well above 50ppm (which is already considered excessive), and last year I really started to see plant health effects related to over-fertilization in high tunnels. I'm happy to announce that I've finally released a 3-part podcast series about this, which includes interviews with soil scientists, vegetable specialists, and freshwater ecologists about how over-fertilization impacts plant health and the environment, and what we can do about it moving forward. If you already saw me talk about this at a winter conference, consider these episodes a deeper dive. I hope you'll listen, and really consider your phosphorus management as you prep your fields this spring. You can stream them here, or look up "The Vegetable Beet" podcast on Apple podcasts, Spotify, etc. 
Episodes include:
  1. Tunnel Trouble: increasing many things, but not yield
  2. Where phosphorus comes from and where it goes
  3. Building organic matter without building phosphorus

Connect with the fruit & veg team

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, and you can submit questions and diagnostic help below. 

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