Hello Folks,
I have a restaurant that is interested in Romaine lettuce all season long. However, I was only really growing romaine lettuce in early and later parts of the season, because I find in the summer heat, the lettuce tastes pretty bitter. I find most lettuce tends to be bitter in summer heat, but romaine seemed to be the most bitter. I tend to grow other varieties mid season, but this restaurant is determined to have romaine.
So what’s the deal with bitter mid season lettuce? Is it a fertility issue, water, or can something be done in post-harvest?
Heat is definitely your enemy here. Lettuce gets bitter in heat or when it is close (or past) bolting. Heat resistant varieties is a good idea, but so is growing lettuce in shaded areas. You could set up an area or a bed with shade cloth tied to some posts for that purpose, which will extend the period before bolting even in high summer heat. If you have natural shade somewhere, use that!
Water-wise, you can’t really water lettuce too much unless you have poor drainage (which would lead to stem rot and attract slugs). You could also mist the lettuce to cool it down, but you can only do that in he shade as water on the leaves of the lettuce in full sun will burn the leaves.
Over the years, I have found variety to make the biggest difference when it comes to bitter or not during the summer. The other thing I have found, especially with some romaines, is the need to keep a close eye on when the plants look like they are starting to think about bolting (which is when they may start to get bitter) and that they may not get as large in the summer as they do in the spring.
I have relied on Coastal Star as a summer romaine for several years but I think there are better varieties. The EFAO tour of William Dam Seeds last August took place towards the end of a hot, dry season on a very hot dry year. Their lettuce had not been irrigated. It was in a sunny spot. I took a really close look at their various varieties and I had a taste of anything that looked good. The two best romaines in their trials were Arroyo and Rainer. Both were better than Coastal Star and Jericho (often promoted as a heat-tolerant romaine but never came out that way in my trials). I have had good luck in the last couple of years with some mini-romaines in the summer, specifically Ansar and Monte Carlo. I’m going to be giving Arroyo a try this year.
I have found Nevada to be the most reliable summer lettuce, especially in terms of bitterness. It’s a Batavian but it works well for ceasar salads. I can easily convince market customers to use it in place of romaine. Not sure a restaurant will be as open to doing so.
You may need to try a few different varieties that other growers and seed catalogues have indicated are heat tolerant, non-bitter, and see which actually work that way in your farm conditions.