It IS possible to grow good lettuce all summer in full sun in Sonoma County. People often have poor results with summer lettuce, eg. it is bitter or bolts (goes to flower) quickly. But if you learn about the variety choices and growing techniques needed for summer lettuce, you can have refreshing, delicious lettuce for your salads, (and BLTs), all summer.
There are so many varieties of lettuce available that choices can be a bit bewildering. Obviously you can look for “heat tolerance” in the description when looking for summer lettuces, but it’s also helpful to know about the basic categories of lettuce types, as some generally do better with heat than others.
The main types of lettuce include: leaf, romaine, butter, bibb, and crisphead (which include both Batavian and iceberg types). All of these can be red or green or color combinations, and there are intermediary varieties that have characteristics of more than 1 type. Although breeders have selected heat tolerance into varieties in all of these categories, in general from my experience, the most heat tolerant are Batavian (also known as “summer crisp” or “French”, and bibb types. And also, in general, greener varieties will do better in heat than dark red ones, as dark colors absorb heat and wilt more readily.
Most people have never heard of Batavian lettuces and they are relatively new to American markets, even though their close cousins – iceberg – are American classics. Batavians have the crunchy, refreshing quality of iceberg but with more of the shapes and colors of leaf lettuces. They usually taste great and are non-bitter and slow bolting. Some varieties you might find include ‘Nevada’ and ‘Cardinale’.
Bibb types are different than butter heads in that they are darker green, crunchier and generally – though not always – smaller heads. Old standards like ‘Buttercrunch’ and ‘Burpee Bibb’ are surprisingly heat tolerant.
In addition, two outstanding romaines for summer are ‘Jericho’ and ‘Toretto’. Both make large, delicious heads.
As mentioned, there are heat tolerant varieties amongst all types, so it is important to KEEP RECORDS of what and when you plant and how it does, as well as talking with other gardeners and reading seed catalogs carefully to find varieties that will do well for you.
But variety choices alone do not guarantee good summer lettuce. The first step is germination, and lettuce seed can go dormant when it gets above around 85 degrees. When whole heads, (as opposed to salad mix), are desired, best results usually come from starting lettuce in containers in potting mix in the shade. If I’m starting lettuce seeds and it gets too hot on my west porch, I move the container to my east porch, which stays cooler. Once the lettuce starts to germinate, I move it to a rack that gets dappled sun/shade under a tree, and gradually move into more sun as it grows. In warm weather it will be ready for transplant in around 3 weeks. I like to start 2, 3, or 4 varieties, which will mature at different rates, once a month from March through September. Lettuce is not a heavy feeder but it has shallow roots which must not dry out and need adequate nutrients to keep up with the fast growth rate of summer. So make sure to add some high nutrient compost or organic fertilizer before planting, and keep soil moist – but not wet. Another tip is to pick whole heads as soon as they fully “head up”. Even the most heat tolerant lettuce can’t be expected to hold for days once it is mature. And lettuce harvested first thing in the morning will taste much better and last longer in your fridge.
Lettuce’s water needs may be a deterrent to growing it in the summer, as we need to conserve water. I supplement my lettuce with my watering can filled with vegetable washing water.
Of course, you could be happy with summer salads of cucumbers, green beans, tomatoes and basil. And it is not too late to plant these crops through this month. Other June tasks include watching your plants grow – pay attention to how they are doing, help your vining crops, (tomatoes, pole beans, cucumbers), onto their supports, and make sure other needs are met. Once summer squash, cucumbers and green beans start producing, pick very often to keep plants productive. If your fruit trees have new growth reaching to the sky, this is a good time to do some summer pruning – removing some current year’s growth to keep tree height down and let more light onto lower branches.
Enjoy the long days and exuberant growth of June.