Last week I wrote about carrots — a vegetable we grow that few other farmers in our area grow.  Another one is lettuce.
Most of the lettuce that grows in the area around our farm is actually a weed:  wild lettuce.  This thistley country cousin bears little resemblance to the stuff in your salad — it’s one of the least palatable plants imaginable, bitter and spiney.  But it thrives in the hot dry weather we tend to have from April until November.  Unfortunately for us, domesticated lettuce does not.
Temperatures over 90 degrees bring out the “wild” instincts of even the most domesticated lettuce, causing it to develop a bitter sap that quickly renders it inedible.  Once the plant turns bitter, a return to cool weather will not eliminate the nasty flavor.  Even very small lettuce plants can be ruined by a spell of just one or two very hot days.
Spikes in temperature from warmer to colder and back can also cause lettuce to “bolt” to seed.  Changes in the length of the day during the crop’s life can have the same effect.  While this is a different physiological process than the one that makes the plant bitter, it has essentially the same result — inedible lettuce.  And lest I forget, lettuce is also vulnerable to damage from very cold weather, with some varieties (like romaine) being more sensitive than others.
There’s a reason why the Salinas Valley — and not the Sacramento Valley — is “America’s Salad Bowl” ™.  The summer weather there is cool, damp and mild.  That keeps lettuce succulent and sweet.  And with little variation in temperatures most of the year, there is little risk of bolting or freezing.
At Terra Firma, we have a short and relatively risky lettuce season.  If we plant it too early in the fall, it is guaranteed to turn bitter.  If we plant too late, it will bolt to seed in late winter before it makes a marketable head.  And even if we do everything else right, freezing temperatures in December (below 26 degrees) can set harvest back by a month or longer — or kill the crop entirely.  Contrast that with another popular salad green we grow — Spinach — which thrives here for 8-9 months of the year.
Over the years, we have experimented with different ways of growing lettuce for our CSA subscribers.  For years we grew only baby-leaf lettuce, avoids the risk of losing the crop before harvest, but creates other issues.  We finally gave that up.
In the last few years we have gravitated towards growing more “mini-lettuce”, new varieties that produce heads more quickly.  The leaves of these varieties are shorter than older type lettuces, making them easier to use in salads.  We’re also trying to identify varieties that are better adapted to our “marginal” lettuce growing conditions.  This year we have mini-romaine, mini-red butter, and mini-red oak, but we’re still keeping our eye out for new releases that might fit in at our farm.
Several subscribers have told us that they really enjoy the lettuce in the boxes, but they can’t find them elsewhere when our season ends.  It’s true that most supermarkets have not kept up with the lettuce trends and are still offering the “old standards”.  However, you can find the mini-head lettuces at most farmers markets.  And several of the pre-washed salad greens producers are now selling lettuce mixes made up mostly or entirely of them.
That said, TFF’s lettuce season begins today, and should continue in some fashion through April — although a weather related gap or two is almost guaranteed.