Lettuce Seeds - John Grow lettuce over winter and keep cropping! One of the best lettuce to grow over the winter to keep your plot cropping. John lettuce is ideal to grow in a greenhouse, cold frame or tunnel throughout winter after you\'ve harvested your tomatoes. A sweet and crunchy \'Butterhead\' variety with pale green leaves and well-filled heads. Downy Mildew resistant making this lettuce variety is ideal to use for winter salads and sandwiches at a time when salad veg are scarce on the plot.