Authors: Natalie Hoidal & Marissa Schuh
It’s a classic Minnesota spring with wild swings between hot and dry to cold and wet. Field work has been delayed on many farms after some parts of the state saw almost 2 inches of rain in 48 hours. A few parts of the state also had frost in the last week. On the horizon, it looks like much of the state should have 4-5 days of dry, warm weather that will allow for tractor work and planting.
Dealing with crusts after rainfall
Soils with lower aggregate stability are more likely to experience some break-down of soil aggregates (clumps) during intense rain events. This is especially true in soils with more clay content. Heavy rains can separate soil into very small aggregates and particles; if the soil surface dries quickly after such an event, these small particles can bind together and form a cement-like surface over the top of your soil. As the weather warms up this weekend and you prepare for planting, what are some options for dealing with crusting?
Use shallow cultivation, setting your sweeps / knives / etc. only as deep as the base of the crust. If you’re growing on a small scale, use shallow hand hoes that barely scrape the surface rather than hoes designed for deeper digging.
Once you’ve planted, keeping the soil surface moist through regular irrigation helps to prevent crusts. Using frost blankets or other row covers also helps to conserve soil at the surface.
Calculating nitrogen credits from compost and manure applications
As you’re prepping fields for warm season crops and finalizing fertility plans, remember to include nitrogen credits from previous applications of manure. Nitrogen in compost and manure can take a long time to become available to your crops. Here's a rough guide to calculating nutrients. While manure can be highly variable, we have estimates for an average amount of nitrogen, phosphorus, and potassium available from different types of manure, reported in pounds of nutrient per ton (English ton - so 2000 lbs) of manure. These estimates are for solid manure, not liquid, see the webpage linked above for more info on liquid manures.
Poultry manure: 52 pounds of nitrogen, 47 pounds P2O5, and 38 pounds K2O per ton of manure.
Beef manure: 18 pounds of nitrogen, 12 pounds P2O5, and 16 pounds K2O per ton of manure.
Dairy manure: 14 pounds of nitrogen, 7 pounds P2O5, and 16 pounds K2O per ton of manure.
In the first year that it's applied, availability really depends on how quickly it gets incorporated into the soil. For example, if you broadcast dairy manure and then incorporate it within 12 hours, you'll get about 60% of that nitrogen. If you wait more than 96 hours to incorporate it, you'll only get 25%. Regardless of how long you waited in year 1, you'll get about 25% of the nitrogen from beef, dairy, or poultry manure in year 2.
1 cubic yard of beef manure is somewhere around 660 lbs. So, let's say you spread around 4 cubic yards per acre last year. That's about 1.2 tons. 18 pounds of N per ton is 21.6 pounds of nitrogen applied to your field total. 25% of that will be available this year, so you'll have just over 5 pounds extra nitrogen, which you can subtract from your total. This isn't a huge amount, but if you're spreading large quantities of manure it can add up quickly.
It’s thistle time
Late spring is one of our key times for managing Canada thistle. For more about managing this tricky, prickly weed, see A war of attrition: Canada thistle management.
Crop specific updates
Asparagus: Harvest is ongoing. With farmers market season ramping up, you might be storing asparagus for a few days before selling it. The optimal storage temperature for asparagus is 32 degrees fahrenheit with 95% humidity. Asparagus with looser tips will go bad faster, so try to sell these spears towards the beginning of the day at farmers markets, and save the spears with tighter tips for later since they keep longer.
Cucumbers, squash, and melons: We’re finally approaching warm enough soils and weather to start planting cucurbits outside in the next week or two. As you plant, remember that cucurbits are extremely sensitive to root disturbance, so handle your transplants carefully. If you have two seedlings in a cell, it is usually not worth trying to break them up. Instead, plant both or cut one near the soil surface. Roots can also be damaged during weed control, so hoe and cultivate carefully. Cucumber beetles tend to show up right after planting, so now is the best time to start planning for them.
High tunnel greens: We tend to see a buildup of aphids this time in the season. While things like biological control and entomopathogenic fungi can keep lower populations of aphids in check, once we get real heat aphid populations can spike, sometimes into something larger than these means of control can keep up with. If populations are growing and you are using a biological control, talk to your supplier about how you might modify your program. What other products can provide control and the threshold will vary by crop; check the Midwest Vegetable Production Guide. Remember, you can select just OMRI products with greenhouse uses.
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| This aphid infestation on spinach is very high. You can see multiple life stages, the shine of honeydew, and the shed exoskeletons of growing aphids. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org. |
Pumpkins: The 24(c) special needs labels for Reflex and Dual Magnum have been approved (previous labels expired at the end of 2025). For a refresher on pumpkin weed control, see Weed Control in Pumpkins and Winter Squash. We are a week or two out from having the 60°F soil temperature that pumpkins need to germinate (most of the state has not hit with any consistency).
Tomatoes & peppers: With the cold and cloudy weather, the transition to hot, sunny weather outdoors may be particularly stark if you’re transplanting next week. In particular, we often see stem girdling and damage right after transplanting these crops into black plastic, where air pockets under the plastic can be 40-50 degrees above the air temperature. Keeping them well watered and being especially careful to adequately harden them off will help with the transition.
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