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How do I grow high-quality fall brassicas?

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Organic farming is a long-term process. Always start the year before by planting a good cover crop, something that will over-winter and return in spring like cereal rye, clover or vetch. If that didn’t happen, or if you’re farming your acreage more intensively, you can also start with a spring cover crop like a mix of field peas and oats. You can research your cover crop options to find the best mix for your soil needs. A good place to start is with the Marbleseed fact sheet “How to Choose Cover Crops“.

To ensure optimal nitrogen value and also create a good amount of biomass for soil microbes without allowing the cover crop to set seed, incorporate the cover crop in early to mid-June. By starting early, but not too early, you leave yourself enough time to work out many of the residual weed seeds in your field. Incorporate the cover crop the first time, then wait 10 days or so and work your field again, by tilling, cultivating or plowing, using whatever machinery and method you usually use for bed prep. Depending on the weather (always), you’ll ideally get another nice weed flush right before you plant. Prep your bed as usual right before planting by cultivating or tilling, then plant your brassica transplants.

The nutritious vegetable that they are, brassicas are heavy soil feeders. Making sure your soil macronutrients are balanced is key. Nitrogen, phosphorus and potassium levels need to be balanced, and not too high or low. Trace nutrients like manganese and boron can also make a big difference in the quality of your brassica crop. Soil tests (soiltest.cfans.umn.edu, uwlab.soils.wisc.edu) applied to fertility practice are important to start with because it’s really hard to make drastic changes in your soil chemistry at any time, especially in the thick of the season.

Some symptoms of out-of-balance soil resulting in nutrient deficiencies:

  • Light yellow color and/or premature head formation also called “buttoning” can be a nitrogen deficiency.
  • Too much nitrogen can cause the plants to grow too fast also resulting in a hollow stem.
  • Large pest infestations can mean your plant isn’t healthy and can’t defend itself.
  • Iron can inhibit calcium uptake, causing localized browning.
  • Phosphorus deficiency, especially when the phosphorus can’t move in the cold of later fall, can cause the plant to turn purple.
  • Boron deficiency can cause a hollow brassica stem, and browning and uneven heads.

Starting with healthy transplants is always essential to healthy produce. One of the most difficult parts of growing fall brassicas is having to care for the transplants in the greenhouse while you’re in the thick of summer harvest. Starting the seeds in a good soil mix, watering consistently, and applying a foliar feed or root drench fertilizer to boost your brassica plant’s health prior to transplanting can make all the difference in the health of your final product. Another option is to create a healthy seed bed in the field, seed with your varieties and bare root transplant from that. For more on this, see the University of Minnesota Extension site .

If you’re buying seed varieties as most produce farmers do, ask the farmers in your area what has worked for them, and also try a few different varieties to find what works for you.

When the plants are in the ground, the best way to balance deficiencies is to either side-dress or foliar feed the plants. Going back to those soil tests and symptom list, you can know what you might need to attend to the health of your growing brassicas and create a mix of fertilizer and minerals in a hopper to be side-dressed once or twice throughout the growth life.

Companies such as Midwestern Bio-Ag can work with you to read your soil tests and provide inputs to balance your soil. You can also try a few different products to find what works best.

At our farm, we foliar feed our brassicas weekly with a fish emulsion mixed with Photo Mag, both OMRI-approved applications. Our soil was in conventional production up until last year, and shows some deficiencies in most everything, including the trace minerals like boron. It’s been really important to give those brassicas feeders good additional nutrition as they grow this season.

Posted: Dec 2016
Answer By: Jennifer Nelson