Winter is so, like, last season.  But, in a moment of reflection, we wanted to share with you the results of our overwintering variety trials. Like many Northeast growers, we took advantage of NRCS’s Seasonal High Tunnel Initiative to put up an unheated high tunnel in 2010.  We’ve been excited to have this year-round growing space, particularly for trialing different varieties of overwintering greens.

Overwintering Heading Crops

This winter was our second year growing in the high tunnel.   One thing that we were curious about was our ability to overwinter heading crops.  From our experience last year, we knew that it was no problem to grow and harvest leafy greens since we had successfully overwintered 12 varieties of spinach and 30 baby lettuce varieties.  We wondered about the feasibility of overwintering small heads of lettuce and heading Asian greens (the choys and the tat sois) for harvest in the early spring.  Many growers already sell salad mix and baby greens; wouldn’t it be cool to offer the season’s first head lettuce?  Or baby pac choy at market? But we weren’t sure these would make it through the winter at all.  Would they size up nicely in the spring or would they immediately bolt?

Mini-Romaine Lettuce Heads Results

We seeded 14 varieties of lettuce in the greenhouse in late September and transplanted them into the high tunnel on November 22. The result?  Gorgeous heads of lettuce ready for harvest, depending on the variety, from the first week of April through the end of the month.  In our zone 4 climate, most growers would be lucky to plant their first head lettuce in the field by the first week of April (under row cover), so this harvest date certainly extends the season by a good month or two.  And, it was such visual candy to peek into the high tunnel and see rows of these colorful, adorable, mini heads!

We planted several varieties of romaine lettuce.  Spretnek  produced bright green, mini romaine heads but was the first to bolt.

Red Tide was the earliest to mature, with large loose heads ready for harvest the first week of April.  This is a gorgeous red leaf variety with a lime green interior and soft leaf texture.  April 10th  trials notes say “Really pretty, full size heads, there isn’t much that’s mini about this variety.  Heads are about 7” across, ready to be harvested.”  During the main season Red Tide produces big full heads; we were excited to see this variety standout in our overwintering trials as well.

Winter Density was another variety ready for an early April harvest.  From the notes again: “Leaf is tender, color is nice dark green; nice stout, low growing head.”

We really liked Pomegranate Crunch, a variety we are hoping to be able to offer in our 2013 catalog.  The color of this variety is uniformly purple/red – striking! It formed nice, dense, squat mini romaine heads.

Breen has been a favorite in our main season trials for mini-romaine heads with striking color (burnished red over pale green).  In the high tunnel, Breen’s color was more subdued – more bronzy than bright – and it elongated before producing much of a heart.  Likewise with Rouge d’Hiver, which produced tall, upright, very loose heads without hearts.

The green leaf varieties we planted like Two Star were slower growing and reached harvest maturity around the third week of April.

Emerald Oak, a nice bright oak leaf variety, produced small heads early on, but we lost a lot of the stand to cold or disease.  A lovely variety, but apparently not a great overwintering one.

Asian Greens Results

Compared to the head lettuce, our Asian green trial was not as successful.  We seeded varieties at the same time as the lettuce, Sept 29 with a November 22 transplant date.  They were planted at 4” spacing in rows 6” apart – tight spacing to promote small heads.  They were ready to harvest at a large braising size, or very (very!) mini head size, in early March.  By late March/early April, all the varieties were bolting (except for the Prize Choy, which produced good size bunches of dark green leaves on thick white stems ready for harvest at this time).

But, we discovered the bolting wasn’t all bad.  Shanghai Green produced tender, juicy stalks with mild brassica flavor and florets about ½” in size.  Tat Soi, too.  Tat soi had a stronger flavor than Shanghai Green, but the stalks were just as tender.  Yukina Savoy, on the other hand, had thicker, stringer stalks – fine for chopping up and cooking, but definitely not as tender.  As a leaf variety, Yukina Savoy is more upright and more bolt resistant than Tat Soi but in its unplanned role as a sprouting brassica, it took the backseat.

We harvested the stalks, at the floret stage, and made bunches with lots of leaf.  Staff took the bunches home and cooked them up in stir-fries.  Delicious!

Efficient Use of Greenhouse Space?

One undesirable aspect of this trial is the tie up of bed space.  Varieties that were planted into the high tunnel in the late fall occupied bed space all winter and weren’t harvested until April.  Since we don’t fire up our greenhouse until March, we don’t have a place to start seedlings in late winter/early spring, so that is partly why we planted in the fall.  What one grower in our area does – and what we’d like to try next season – is transplanting head lettuce and bok choy into the high tunnel in March.  The harvest date might not be quite as early, but you’re not tying up all that bed space through the whole winter.  We haven’t tried it, but we can imagine a succession planting plan for direct seeded spinach or leaf lettuce in the fall, followed by transplanted heading varieties in the early spring for a nice diverse crop offering.

In a separate trial, we seeded Shanghai Green on Sept 5 and transplanted into the high tunnel on Oct 6.  The planting date resulted in gorgeous, tight mini heads ready for harvest at the end of November.

In northern climates, the winter growing movement is exciting and it’s wonderful to see so many of our customers extending their season and providing more local produce to their communities and families. We’ll continue to share our experiences with you all, and hope that likewise, you’ll let us know what you’re excited about and what’s working well for you.

Now, onward to summer!