Our New Cover Crops

Cover crops have many benefits for the garden.  A cover crop is simply a plant grown, not to harvest, but for its benefits to the soil.  You can grow cover crops anytime that you have a spot in the garden that doesn’t have a crop growing in it.  Fall and winter are a great time to have cover crops in St. Louis, as the garden is usually bare unless you are growing some type of overwintering crop like garlic.  

Cover crops have the ability to improve soil quality by adding organic matter and nitrogen.  They also cover the soil surface, meaning less erosion and fewer weeds will germinate.  Possibly the biggest benefit that cover crops have is that they feed the beneficial microorganisms in your garden soil.  These organisms feed off the compounds that living roots exude into the soil and dead organic matter as mulch.  Feeding these organisms improves nutrient availability and soil structure, making it easier to dig and easier for water to absorb into the soil.

In the past we have offered several types of cover crops made of single species or a blend of two species but increasing research on cover crops has shown that having more species in your mix increases the benefits of cover crops.  In addition, our increasingly warm winters have meant that cover crops that used to be killed by the winter are now surviving the winter more years than not.  Due to both of these facts we have changed our cover crop offerings to just two blends to simplify things and increase the effectiveness of the cover crops.

The first blend is the “winter kill blend.”  This is a blend of 4 species of cover crops that were selected to die when the coldest part of winter comes.  This type of cover crop should be planted in September so there is enough time for the cover crop to grow before the cold kills them.  The winter kill blend can be a great choice if you don’t want to have to worry about killing the cover crop in the spring.  It is also the best option if you want to plant cool season crops where the cover crops will be growing.  This blend includes oats, berseem clover, phacelia, and tillage radish.  Oats are particularly good at adding carbon to the soil and feeding beneficial organisms.  Berseem clover is one of the best nitrogen fixers so it can add fertility to the soil.  Phacelia blooms over a long period, helping to feed and sustain beneficial insects in your garden.  Tillage radishes wide arching leaves help to quickly cover the soil, reducing weeds, and their large tap roots help to break up compaction and increase water infiltration.

The second blend is our “overwintering blend.”  The “overwintering blend” is a combination of 4 cover crops that were selected to reliably survive our winter.  Overwintering cover crops can be a great choice if warm season crops are more important in your garden.  This blend can be planted as late as mid-October, right around when you are ripping out your warm season crops.  It then grows throughout the winter and spring and is ready to be killed or removed around the end of April, just in time to plant your warm season crops again.  The 4 species of this blend are annual ryegrass, winter rye, crimson clover, and winter peas.  Annual ryegrass creates a short dense turflike growth with a dense mat of roots holding and covering the soil, reducing erosion and weed germination.  Winter rye adds an enormous amount of carbon to the soil and provides support to the winter peas.  Crimson clover adds nitrogen to the soil and produces flowers to feed beneficial insects in the garden.  Winter peas also fix nitrogen in the soil while also being edible.  The tender growing tips of pea plants are delicious all winter long.

Best Bok Choy for St. Louis

by: Dean Gunderson

Bok choy is a delicious and nutritious vegetable that is pretty low maintenance to grow in St. Louis, EXCEPT, it tends to quickly bolt once it gets hot.  Given St. Louis’ erratic spring weather this tendency can be a huge problem.  It’s not unusual for us to hear from gardeners who had their bok choy bolt and stop producing before the plants were even big enough to harvest.  So this spring we did a variety trial with the goal of identifying one or more varieties of bok choy that were resistant to bolting and produced well in St. Louis and we are happy to say we found 3 varieties that did exceptionally well.  Before we get into that let’s first talk a little about bok choy.

Bok Choy Background

Bok choy is a member of the brassica family.  But it is Brassica rapa, not Brassica oleracea (the species that includes cabbage, broccoli, cauliflower, kohlrabi, brussels sprouts, collards, and kale).  Like Brassica oleracea though Brassica rapa is a species that was domesticated into many different crops.  Brassica rapa includes bok choy but also turnip, tatsoi, broccoli raab, napa cabbage, komatsuna, field mustard, and several other types of less common greens.  

Although Brassica rapa is from somewhere in Eurasia, the exact location of its original domestication is debated.  However, bok choy specifically is generally accepted to have been developed in the Yangtze River Valley of China.  From there it spread throughout East Asia and then to the rest of the world.  As its place of origin, and where it is still the most popular, China has the greatest diversity of bok choy varieties and where the bulk of the world’s bok choy is still grown.

When bok choy was developed there were two main types that were developed; green stemmed and white stemmed.  Green stemmed varieties are generally speaking more forgiving and adaptable.  White stemmed varieties are generally the ones you will see at the store because the brilliant white colored stems look nice and they tend to be more juicy and crunchy.

the bed showing all the bok ahoy in the trials
Here you can see all the bok choy in the trial on May 20th. You can see on the right that one variety has already bolted and another is in the process of bolting.

Our Test

In an attempt to find a variety that would grow well in St. Louis, despite our erratic springs/summers, we identified 7 varieties that were claimed to be the most heat and bolt resistant.  The 7 we tried were:

  1. Chun Mei
  2. Chun Yu
  3. Jimao Choi
  4. Mei Qing Choi
  5. Extra Dwarf Pak Choi
  6. Hotau Improved
  7. Joi Choi

One by one extra dwarf pak choi, mei qing choi, hotau improved, and then jimao choi bolted with extra dwarf bolting in mid-May and Jimao bolting by mid-June.  Even these varieties that “failed” did quite well considering how most bok choi performs in a St. Louis spring.  Hower joi choi, chun mei, and chun yu left the others in the dust.

Joi Choi

Someone holding a head of job choi showing the large white stems.
A head of joi choi that was harvested mid-June.

Given that white stemmed varieties tend to be more picky about their weather than green stemmed varieties we were shocked when joi choi, a large bok choy with thick succulent white stems, was one of the last to bolt in our test.  The other white stemmed varieties in our trial bolted in May.  Joi choi bolted over a longer period of time than the others, where all individuals of the same variety bolted within a week.  The first one started bolting in the second week of June but we didn’t end up harvesting the bulk of the joi choi until the end of June which is impressively late.  By this time those plants had endured many days in the 80’s, 90’s and even a day that reached 100 degrees.

chun yu and chun Mei in mid-June looking healthy
Mature heads of chun yu and chun mei in mid-June

Chun Yu

Chun yu is a green stemmed variety that produces baby sized heads.  It never actually bolted but by the first week of July it was starting to elongate and look a bit ragged so we harvested it.

Chun Mei

Shows what chun mei looked like when we harvested them.  Slightly elongated and a bit ragged looking but still healthy and delicious
This is what chun mei looked like in mid-July when we finally harvested them. Although they may not be the prettiest they still tasted great, with no bitterness.

The winner of the trial.  Chun mei was almost identical to chun yu in size and look but seemed a bit more bolt resistant than chun yu.  Like chun yu it never actually bolted but started elongating and looking ragged in July.  Unlike chun yu though this didn’t happen until mid-July!  This is incredibly late in the season to harvest bok choi that hasn’t been protected from the heat in some way.  By the time we harvested the chun mei those plants had endured 38 days of temperatures in the 80’s, 15 days of temperatures in the 90’s and even a day that reached 100 degrees.  Not too shabby for a cool season crop prone to early bolting.


All of the varieties we tried did comparatively well against most bok choy we have grown in the past but if you are looking to grow a large bok choy and/or a white stemmed bok choy, joi choi is a great one to grow.  If you want to grow a green stemmed and/or baby bok choy, try the varieties chun yu or chun mei.