First weekly vegetable update of 2026 - May 7 2026

UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

The beginning of the growing season has been relatively gentle, all things considered. Last week at this time, we had record breaking heat and wild fires. While most of the country is under some amount of drought right now, most of Minnesota has normal soil moisture levels. We've had a nice mix of warm days for field work, a little bit of rain, and plenty of cool weather in between. The main problems we're seeing so far are familiar: potting soil problems, and planting too soon. 

Nitrogen troubles

Every couple of springs we see a big batch of potting soil that's not quite right. I've seen nitrogen deficiencies in a lot of flats this year. If your seedlings are looking yellow overall, especially on the bottom leaves, and seem to be growing slowly, it is likely a nitrogen deficiency. Applying fish emulsion to your flats is an easy way to give seedlings a boost. Some people also make a slurry of blood meal in warm water. 

Brassica transplants with a nitrogen deficiency. Photo: Natalie Hoidal, UMN Extension.

Planting too soon

Every year we get a flush of warm weather, and we all get the itch to start planting. We are still very very likely to have a frost across most of the state, so hold off on planting those warm season crops like tomatoes, peppers, and especially cucumbers. Even if we don’t get a hard frost, they do not thrive in cool weather. 

What about in a high tunnel? It really depends... if you're not using any supplemental heat, there's still a risk of a hard frost injuring high tunnel tomato and cucumber plants at this point. I've seen tomato plants get killed by a hard frost in mid to late May in a high tunnel plenty of times. If you are heating your tunnel, you can go ahead and plant. But even in a heated tunnel, your plants will be a bit stressed if your nighttime temperatures are consistently below 60 degrees F. 

A tomato transplants damaged by multiple rounds of frost in an unheated high tunnel. Photo: Natalie Hoidal.

Soil temperatures outdoors are hovering between 45 - 55 degrees Fahrenheit right now, meaning it's a perfect time to plant things like beets and carrots, but still on the riskier end for direct seeding sweet corn and beans, which are more likely to have seedcorn maggot damage if they are planted into cool soils. Some growers do transplant sweet corn onto plastic this early in the season... We just learned that our colleague Charlie Rohwer is planting an early sweet corn trial this week to identify varieties that do well with a really early planting date, so we'll be excited to share those results with you next year! 

The wonders of a heated greenhouse

If you are going to plant heat loving crops early, a heated greenhouse is critical. Below is a photo from a heated greenhouse in central Minnesota, which is already producing cucumbers, basil, tons of lettuce, green onions, and in a few weeks, a first succession of carrots. The tradeoff here is propane. Whether it's worth it to heat a greenhouse is really a matter of whether you have a market for early spring crops, how much your market is paying for those early crops, and how much propane you are comfortable using. We’re learning more about technologies like “climate batteries” and other more passive means of heating high tunnels and greenhouses, but we still have a lot to learn before we have clear guidelines and cost / benefit estimates. 

A propane heater has allowed for a lot of crop growth in this heated tunnel. Photo: Natalie Hoidal, UMN Extension

Crop specific updates

• Asparagus: Asparagus harvest is already underway. It’s been chilly and windy, so if you’re seeing bent spears, it could either be weather or asparagus beetle. Asparagus beetle management is tricky – sprays should be timed for peak beetle activity (warm, sunny afternoons) and products need a short pre-harvest interval. For example, in organic production, Entrust is labelled for asparagus beetle but has a 60 day PHI, meaning we can’t use it until we are done harvesting. For conventional growers, there are a couple of options, check the Midwest Vegetable Production Guide for information.

• Garlic: The garlic we’ve seen so far this year looks pretty good. Winter survival seems better than last year, though this is purely observational based on the few farms we’ve visited so far. We are nearing the final days where we would recommend spring fertilizer applications, and many growers may already be past this point. Try to avoid fertilizing after your garlic has reached 4-6 inches, as too much nitrogen at this stage of development can hinder bulb growth. Each year we’re seeing more and more widespread aster yellows, as well as other viruses. Check for plants that are extra yellow and stunted, and remove them to reduce potential problems later this growing season.

• Brassicas: early planted Brassicas are getting established in fields. This will be a good week to start transplanting things like broccoli, cabbage, and cauliflower.  Cabbage maggot has started to emerge from its overwintering locations in the southern half of the state, and flies will continue to be out and laying eggs for a few weeks (depending on how warm the weather is going forward). When these flies are out, they are looking to lay eggs on brassicas, a row cover is the best method of prevention, especially if you have a history with this pest.

• Other greens: We’re getting close to the transition time between choosing varieties that are well suited for early spring plantings, and varieties that need to be more heat tolerant for summer harvest. 

• Potatoes: many growers in southern MN planted potatoes last week. We got one question about whether planting late could help alleviate potato beetle damage. The answer (as usual) is… it depends. Colorado potato beetles spends the winter in field edges (either in the soil or in plant debris), and they start to wake up when temperatures are above 50°F.  They will wait in the soil to warm up for 50 to 250 (base 50) degree-days (a unit entomologists use to capture how much warmth an insect has experienced).  This translates to…Colorado Potato Beetles need a period of time where temperatures are above 50° to dig themselves out of the soil.  Once out, they use some combination of sight and smell cues to find emerging potatoes. I’ve seen instances where the beetles are out of the ground before the potatoes, but the beetles are hanging out in the soil in the spots where potatoes have planted. So why would late planting help? Adult Colorado potato beetles we see in the spring don't tend to get too far, they often don’t fly, so wherever they can waddle is where they’ll end up. The goal in planting late is that we are planting after these beetles have emerged and have starved. This will likely be part of an integrated approach for dealing with Colorado potato beetle, if trying it, make sure you will still have enough season after planting late to reach your yield goals.

• Onions: This week is a good time to plant onions in the southern and central parts of the state. Do you need to trim them? Many people say you should trim onions before transplanting to help them grow more quickly, and to encourage stronger leaves. Whether this actually improves onion hardiness is up for debate. It certainly doesn’t hurt, but it’s not clear that it’s worth the time to do so. 

• Beets and carrots: This is a great week to seed your first succession of beets and carrots. If you don’t have a super smooth seedbed, using row cover can help preserve moisture in the top layer of soil, which can improve germination. 

• Sweet corn: Use soil temperature to pick when you plant. Check the soil temperature maps in your area and wait until temperatures get closer to 60°/65°F consistently to plant your sweet corn. Planting before the soil is warm enough will delay germination, increasing chances of root rots and making succession plantings all come up at the same time. Seedcorn maggot is flying across Minnesota, if you have a history of damage from this pest, have a protection measure in place for plantings going out.