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May 3, 2021 |

The Wonderful World of Overwintering Brassicas

By: Dean Gunderson

When you have a garden in St. Louis you have plenty of produce in the summer and fall and usually well into winter through things like squash, sweet potatoes, cold hardy greens, and by ripening green tomatoes inside.  With some pretty low tech season extension like low tunnels it’s also easy to overwinter cold hardy greens like collard, kale, spinach, and turnip greens in order to have fresh produce all the way until those bolt, usually in March.  Unless you are doing indoor or greenhouse gardening though there is usually a gap from March (after the greens bolt) until well into May where there isn’t much of anything you  can harvest from the garden other than maybe some early planted greens or green onions.  

Before widespread food distribution networks this period was called the ‘hungry gap.’  Knowing that people want and/or need good fresh produce from their garden all year and not just part of the year we have experimented with different crops over the last couple years to try and find ways to help fill this ‘hungry gap’ in St. Louis gardens.  Europe’s climate has a similar ‘hungry gap’ in their growing season and the people of western Europe have spent many centuries trying to fill that ‘hungry gap.’  Those crops for the most part have not been grown here because our winters are more extreme than the parts of Europe where those crops were developed so they couldn’t overwinter here.  However, given the heat island effect of growing in a city, our increasingly warm winters, and the accessibility of cheap and effective coverings like row cover and low tunnel plastic that can keep the plants a bit warmer we thought these crops were worth a try. 

OUR FIRST WINTER BRASSICA – SPROUTING BROCCOLI

shows the large leafy sprouting broccoli plants under a low tunnel

Sprouting broccoli plants in Mid-January

A few years ago we tried growing our first winter brassica, sprouting broccoli, in order to fill the ‘hungry gap’ and it was a big success.  We planted it in the fall at the same time we planted our fall broccoli, cabbage, kale, and collards, covered them with a single layer of row cover, and by mid-March there were small broccoli heads forming on the plants, before we had even planted our spring planted broccoli.

shows the mature sprouting broccoli florets ready for harvest

Sprouting broccoli florets on March 25th

Although sprouting broccoli produces smaller heads than newer broccoli cultivars they are a nice hearty addition to that early spring garden.  They also produce many side shoots and you can keep harvesting from them for several weeks. 

After growing sprouting broccoli successfully for several years we decided to investigate if there were other “winter brassicas” that we could trial in order to see if they could successfully survive our winters.  We were able to get seed for 3 varieties of winter cabbage and 4 varieties of winter cauliflower and decided to do a variety trial.  Although this is the first year we have grown them and we will need to grow them for several more years to verify our results, our initial trial was very successful.  We will go through what varieties we tried, how we grew them, the results, and what we would recommend if you want to grow them yourself.    

WINTER CABBAGE

When we were looking at winter cabbage varieties we wanted to find the most cold hardy variety of green cabbage, red cabbage, and savoy cabbage.  The three varieties we tried are listed below. 

     Winter King: a standard looking green cabbage

     January King: a beautiful purplish green cabbage

     Omskirk: a savoyed green cabbage

Winter cabbage is different from sprouting broccoli and winter cauliflower, it’s really just a more cold tolerant cabbage.  So like any other fall vegetables they need to be planted early enough to be full grown by the second half of November at the latest.  If they are mature by then, due to their cold tolerance they can just hang out in the garden all winter and you can harvest them whenever you need cabbage.

All three of the cabbage varieties survived our winter just fine.  They were unprotected for all of the winter except for the week long period in February when temperatures were unusually low.  For that week we covered the cabbage with a layer of low tunnel plastic and a layer of row cover.  We did this because we wanted to make sure at least some would survive so we would know which was the most cold hardy.  Low and behold they all survived with virtually no damage beyond a leaf or two with a little freeze damage on the edge of the leaves, despite the fact that there were several days in a row where the temperature never got above 5 degrees.  This would suggest that we didn’t need to cover them as much as we did, or possibly at all over the winter.

It’s important to note at this point that we planted our winter cabbage too late.  We didn’t get the seedlings in the ground until mid-September so they did not have heads on them by the time winter started.  Since cabbage will bolt by the time spring comes we did not actually get any fully formed cabbage heads.  However, the cabbage plants did start forming heads before they bolted, they just didn’t fully mature before they bolted and there were noticeable differences in how they grew that are interesting to note to inform further grow trials.  

‘Winter King’ was probably the least successful variety.  They were slower growing than the others and several of them started trying to form multiple heads in late winter instead of just one.  They also were definitely the smallest plants and heads by the time they bolted and several of the individual plants didn’t make it to spring.

‘January King’ was by far the prettiest cabbage I’ve ever seen and did quite a bit better than ‘Winter King.’  All of the ‘January King’ plants survived the winter.  They also started forming heads, which got pretty large, before they bolted.   

‘Omskirk’ seemed to be the best of the three varieties.  They all survived and had really no leaf damage over the winter.  They also started forming heads in the fall and then they kept growing in the spring.  Due to this they were the largest plants and had the largest heads of all three of the varieties.

WINTER CAULIFLOWER

Winter cauliflower was definitely the big success story of our trials in the winter of 2020-2021.  We were able to get seeds for four varieties.  The varieties are listed below.

     Prestige

     Corella

     Chester

     Fredor

Like the winter cabbage the winter cauliflower were planted in mid-September and left uncovered until the cold snap in February when they were covered in the same way.  ‘Prestige’ didn’t survive the winter but the other three varieties survived.  They each had some frost damage on the leaves but recovered just fine.  So like the cabbage it seems possible that they didn’t need as much coverings as we provided them during the cold in February.

shows several mature cauliflower heads

Mature ‘Corella’ and ‘Fredor’ Cauliflower

‘Corella’, ‘Chester’, and ‘Fredor’ all produced well.  ‘Corella’ and ‘Fredor’ both started producing around April 15 and we harvested the last head off of those varieties on April 27th.  April 27th was also the first day we harvested heads off of ‘Chester.’ 

shows a chester cauliflower head

A ‘Chester’ cauliflower head

‘Chester’ produced the most ideal looking cauliflower heads of the three varieties but the weather was much more erratic when the heads of ‘Corella’ and ‘Fredor’ were forming so it’s unclear if the difference was due to varietal differences or weather differences.  We will have to grow them again to know that.  However, we can say that all three varieties produced heads that were very flavorful and tender. 

HOW TO INTEGRATE WINTER BRASSICAS IN YOUR GARDEN

We will continue to experiment with these interesting varieties but if you want to try them yourself in order to be able to harvest more than greens from your garden in the winter and early spring below is what we would recommend.

The most important thing is to make sure you get them planted early enough.  Seedlings for the winter cabbage should be planted in the first half of August to assure they have enough time to mature before winter.  Sprouting broccoli and winter cauliflower should be planted as seedling between the beginning of August and the third week of September to make sure they are established before winter sets in.

We also recommend to be prepared to cover them.  As we discussed above covering isn’t necessary unless the temperature become very cold but what exact temperature they need protection from is unclear.  Until we have a more clear picture of how hardy these plants are we recommend covering if the temperatures are predicted to get down into the mid teens or lower, although again, as discussed above, that might not be necessary.

shows a small 1" diameter cauliflower head forming

A newly emerging cauliflower head on April 7th

If you are wanting to increase the food produced in your garden throughout the winter and early spring we recommend growing a combination of winter cabbage, sprouting broccoli, and winter cauliflower.  You should be able to harvest the winter cabbage as needed all winter until about Mid-March when it starts to bolt.  Conveniently, it was around this same time on March 15th that we got our first harvest of sprouting broccoli this year.  The sprouting broccoli continued to produce until April 7th, when we harvested the last ones and ripped out the rest of the bolted plants.  It was on this same day that we saw our first cauliflower heads forming and then a week later on April 15th we harvested our first cauliflower from the ‘Corella’ and ‘Fredor’ varieties.  Then on April 27th we harvest the last of the ‘Corella’ and ‘Fredor’ heads and the first of the Chester cauliflower heads. 

So if you plant winter cabbage, sprouting broccoli, and ‘Corella’ and/or ‘Fredor’ cauliflower, and ‘Chester’ cauliflower you could potentially be harvesting nice hearty brassicas fresh from your garden from early December all the way through early May!

So we will grow these varieties this winter, along with a few more winter cauliflower varieties we were able to get seed for this spring, and continue to trial them going into the future.  We will also of course continue to share our findings with all of you.  If you grow them we would also love to hear your results to add information to our trials.