Authors: Natalie Hoidal & Marissa Schuh
It is dry, great for field work, but a little unnerving. Portions of the state are abnormally dry and a few spots have tipped over into moderate drought, but we are avoiding the drought a lot of the country is in. NOAA’s last release of seasonal precipitation and temperature forecasts are giving an equal chance of above or below average precipitation (we are due for new seasonal forecast releases soon). 10 day forecasts are showing a pretty good chance of rain sometime Sunday through Tuesday for much of the state.
We tend to tell people to wait until June 1 to plant their most tender crops, just to be really safe. Most years, mid May is totally fine, but every so often we get a late spring frost that decimates tomatoes, peppers, and cucurbits. This year, it’s looking like we’re very very likely in the clear in the southern part of the state, but currently lows next Tuesday are projected to fall around 35 degrees in northern Minnesota. On a 10 day forecast, that’s enough risk that I personally would wait to plant.
Beets and carrots: With already dry conditions and uncertainty about rain in the forecast, it’s going to be a tricky week to germinate your small seeded, direct seeded crops. Irrigation will be critical. And row cover really does help to conserve soil moisture. Some growers go as far as using a full on tarp (e.g. a silage tarp). The trick is to plant something that germinates more quickly than your carrots or beets (like radishes), so that you can pull the tarp off right before your carrots / beets germinate so that you don’t accidentally kill them.
Brassicas: Cabbage maggot has emerged now from its overwintering locations everywhere south of St. Cloud, and we are likely to see them emerge in the northern half of the state in the coming week. They’ll be flying for the next few weeks, so now is the time to cover your Brassicas. There are very limited treatment options since they lay eggs in the soil near your plant roots, and so physically preventing them from laying eggs with row cover is your best bet. Once they lay eggs, they can do extensive damage to radishes, turnips, broccoli, collards, and anything else in the Brassica family.
Cucumbers, squash, melons: definitely wait at least a week. If you can’t wait, you might be fine, but you also might have some cold damaged plants.
Garlic: We’re hearing reports of yellow garlic tips. What can cause this? A few things: garlic tips can turn yellow with cold damage. They can also turn yellow when there’s too much or too little moisture. It can also be a sign of nitrogen deficiency. We’re starting to push past the recommended window for side dressing garlic with fertilizer, but if you suspect a nitrogen deficiency, it’s still worth fertilizing. Do it as soon as possible to avoid delaying bulb setting.
Tomatoes and peppers: Wait a week if you can (or two in northern MN) to plant outdoors. If you can’t wait, you’ll probably be fine in the southern part of the state.
Potatoes: Colorado potato beetles is starting to emerge in the southern portion of the state. Get an update on different management tactics in our article "Colorado Potato Beetle Refresher."
It is dry, great for field work, but a little unnerving. Portions of the state are abnormally dry and a few spots have tipped over into moderate drought, but we are avoiding the drought a lot of the country is in. NOAA’s last release of seasonal precipitation and temperature forecasts are giving an equal chance of above or below average precipitation (we are due for new seasonal forecast releases soon). 10 day forecasts are showing a pretty good chance of rain sometime Sunday through Tuesday for much of the state.
Still deciding how to deal with crop residue or an overwintered cover crop?
If you have a lot of crop residue in your fields, you have a few options. Check out recent video about methods for terminating cover crops if you’re still deciding what to do with overwintered cover crops like rye, vetch, or winter wheat.
The obvious answer is to till residues into the soil if your goal is to plant as quickly as possible. While tilling is harmful to soil structure and can cause long term compaction issues, it’s efficient and can be the best tool when a lot of residues are left on the soil surface. However, it’s not always necessary. Some alternatives include:
The obvious answer is to till residues into the soil if your goal is to plant as quickly as possible. While tilling is harmful to soil structure and can cause long term compaction issues, it’s efficient and can be the best tool when a lot of residues are left on the soil surface. However, it’s not always necessary. Some alternatives include:
- Using a wheel hoe with a basic stirrup attachment is surprisingly effective at getting a field sufficiently clean for transplanted crops. The practicality of this depends on your scale, and how much time you have available. In the photo below, the high tunnel soil was really really compact (and rocky), with quite a bit of surface residue. A broadfork and wheelhoe were able to loosen the soil and incorporate residues with much less disturbance and soil turning than a rototiller would have done.
- If you’re at a larger scale, consider whether a shallow (1-3 inch) cultivation pass with something like a harrow, or cultivating knives will do the trick. The less deep you can till, and the less you can turn the soil over, the better for soil health. On the flip side, you want to choose a method that will disturb things enough that you don’t have to go back and do it again.
- If you’re still not going to plant for a while (e.g. in beds where you’ll plant carrots or broccoli in mid to late June for fall harvest), using a tarp for ~4 weeks in the spring can often effectively kill a cover crop or weeds. Tarps tend to hold moisture in the soil nicely, and a tarp + a wheel hoe, or a tarp plus shallow tillage can work just as well, if not better than really deep tillage.
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| Grad student Ben used a broadfork and stirrup hoe on attachment on a wheel hoe to loosen some very compact high tunnel soil and incorporate surface residues before planting. |
How likely is another frost?
We tend to tell people to wait until June 1 to plant their most tender crops, just to be really safe. Most years, mid May is totally fine, but every so often we get a late spring frost that decimates tomatoes, peppers, and cucurbits. This year, it’s looking like we’re very very likely in the clear in the southern part of the state, but currently lows next Tuesday are projected to fall around 35 degrees in northern Minnesota. On a 10 day forecast, that’s enough risk that I personally would wait to plant.
If you’re in the southern part of the state, waiting doesn’t hurt. We’re still looking at plenty of nights in the high 40s / early 50s, which is cooler than tomatoes like to be, and a lot cooler than cucurbits like to be. These crops won’t grow much over the next couple of weeks, and so… if your tomatoes and peppers are starting to get stressed indoors, go ahead and move them out. If you still have space for them and they’re doing fine inside, they’re unlikely to benefit much from moving out early. Cucurbits (cucumbers, melons, squash) are especially sensitive to the cold; keep them indoors at least another week if you can help it.
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Some patchy sweet corn survival after a cold recently night. Charlie Rohwer
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| Some patchy sweet corn survival after a cold recently night. Charlie Rohwer |
Timing your spring nitrogen fertility
Many Minnesota vegetable farmers have plenty of phosphorus and potassium in their soil already, and mostly need to add nitrogen. For organic growers, your options for nitrogen only fertility sources are animal byproducts like blood meal or feather meal (both about 12% nitrogen), and ground up crop products like soybean meal, peanut meal, soybean hydrolysate, or corn gluten meal. Conventional growers have access to products like urea. If you’re adding nitrogen-rich fertilizers this spring, consider the following:- Seedcorn maggot and cabbage maggot are attracted to freshly applied / decomposing organic matter. Seedcorn maggot feeds on the seeds of large seeded crops (corn, beans, peas, and cucurbits (squash, melons)), while cabbage maggot feeds on all the brassicas. The A colleague recently recommended working organic N sources like bloodmeal into the soil about 2 weeks before direct seeding to avoid luring in the seedcorn maggots. (Planting when the soil is warm enough will also help - seeds that are just sitting in cold soil vs. germinating are more vulnerable).
- Aphids love nitrogen. In general this means they like to eat fresh, nitrogen rich young plants. Specifically, there is some evidence that they reproduce more quickly when nitrogen levels are in excess. Following soil test recommendations and accounting for nitrogen credits can help you to avoid excess nitrogen - and will also save you a lot of money in the long run. (Our steps for calculating nitrogen credits are on the high tunnel fertility webpage at the moment, but the same principles apply to fields!)
- Timing: Nitrogen availability is highly variable across organic inputs, and depends on soil moisture and temperature. Since microbes have to break organic nitrogen down into plant available forms, and microbes work best when they are in soil that is perfectly moist and an ideal temperature, actual release rates vary quite a bit from year to year, and from place. In general though….
- Plant-based compost releases nitrogen very very slowly. Less than 10% of the nitrogen in it is released in a typically growing season. Yard waste compost is unlikely to provide enough nitrogen for your plants to thrive unless it’s paired with another input.
- Composted poultry manure products (e.g. Sustane, ChickNpoo, etc.) also release nitrogen slowly, though not quite as slowly. We usually assume somewhere around 30-50% of the nitrogen in composted poultry manure will become available in the first year, though some commercial products are mixed with other things that allow a bit more nitrogen release.
- Inputs like feathermeal or bloodmeal release plant available nitrogen more quickly, with most of the plant available nitrogen becoming available within a month or so of application. This means that if you’re relying entirely on products like bloodmeal or feathermeal for fertility, you should consider applying part of your fertility up front, then side dressing (or fertigating, or applying with a backpack sprayer) a couple of times throughout the season. This mostly important for long-season fruiting crops like tomatoes, cucumbers, or peppers.
- For anyone who wants more of a deep dive, here’s a nice article from UC Davis comparing nitrogen release rates of different organic inputs.
Crop specific updates
Asparagus: Harvest continues. Both common and spotted asparagus beetles are out, causing bent spears and damaging tips. Get management advice in “Tips for Managing Asparagus Beetle.”Beets and carrots: With already dry conditions and uncertainty about rain in the forecast, it’s going to be a tricky week to germinate your small seeded, direct seeded crops. Irrigation will be critical. And row cover really does help to conserve soil moisture. Some growers go as far as using a full on tarp (e.g. a silage tarp). The trick is to plant something that germinates more quickly than your carrots or beets (like radishes), so that you can pull the tarp off right before your carrots / beets germinate so that you don’t accidentally kill them.
Brassicas: Cabbage maggot has emerged now from its overwintering locations everywhere south of St. Cloud, and we are likely to see them emerge in the northern half of the state in the coming week. They’ll be flying for the next few weeks, so now is the time to cover your Brassicas. There are very limited treatment options since they lay eggs in the soil near your plant roots, and so physically preventing them from laying eggs with row cover is your best bet. Once they lay eggs, they can do extensive damage to radishes, turnips, broccoli, collards, and anything else in the Brassica family.
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| Cabbage maggots feeding on Brassica roots. Photo: UMN Extension website |
Cucumbers, squash, melons: definitely wait at least a week. If you can’t wait, you might be fine, but you also might have some cold damaged plants.
Garlic: We’re hearing reports of yellow garlic tips. What can cause this? A few things: garlic tips can turn yellow with cold damage. They can also turn yellow when there’s too much or too little moisture. It can also be a sign of nitrogen deficiency. We’re starting to push past the recommended window for side dressing garlic with fertilizer, but if you suspect a nitrogen deficiency, it’s still worth fertilizing. Do it as soon as possible to avoid delaying bulb setting.
Tomatoes and peppers: Wait a week if you can (or two in northern MN) to plant outdoors. If you can’t wait, you’ll probably be fine in the southern part of the state.
Potatoes: Colorado potato beetles is starting to emerge in the southern portion of the state. Get an update on different management tactics in our article "Colorado Potato Beetle Refresher."
Sweet corn: Soil temperatures are just starting to reach 60°F in southern Minnesota. Seedcorn maggot is at its peak south of Alexandria / Mora. You could plant sweet corn, but it might be better to wait until the beginning of next week. Seed that sits in cool soil is less likely to germinate quickly, and more vulnerable to seedcorn maggot. The good news is, soil temperatures warm up really quickly this time of year.
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| Mariusz Sobieski, Bugwood.org |
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