Varietal differences plus the growing methods can't really be compared. Soil in a window box will dry out 100x faster than the commercial varieties grown in the ground. Lettuce is a water hog since it is 90% water to begin with. But that soil moisture level must be consistent and that is impossible to do in a windowbox.

Water it well with cold water 1 hour before harvesting it for the most crispness the particular variety will allow. Also don't let the leaves get too big/old before harvesting.

Dave

It's probably because they're different varieties, and because they're young. Some types of lettuce are crisper than others.

A window box is a furnace on a hot day.

I find the Romain and bib type the best for container growing. A drain pan under the container to hold extra water can be of some help along with a good soil mix like Al's 5 1 1 and watering every day. ( you will find Al's 5 1 1 over on the container fourm ) Still growing lettuce as crisp as the store type (Iceberg) in a window box would be a challange. I for one no longer care and seldem buy at the store I enjoy the taste and varity of all the other lettuce's including the leaf types

Curt

Tom Thumb is a butterhead lettuce, supposed to be less crisp.

thanks a lot for all the responses. I will not let the soil dry out and try the cold water tip. Also though the lettuce is planted in a window box, it just stays on my covered front porch which gets some morning sun, so mostly its in partial shade with the radishes in another window box.
Next year I will surely give it a try in the ground and see if there's a difference.

I've been growing lettuce in containers for several years and thought they did well - until this year when we put in raised beds. The difference in the lettuce is so remarkable that I changed my mind about growing some in containers near the kitchen door. The quality of the lettuce this year is well worth the walk to the garden.

I find that picking lettuce a couple hours ahead, soaking in very cold water for a few minutes, and then refrigerating it gives even the softer lettuces maximum crispness. Goes against how I like to pick everything as fresh as possible, but works pretty well for me.