If you’re growing lettuce for seed, you’ve got all season and several key growth stages when it’s easy to spot off-types and rogue them out. By the time lettuce plants start flowering, the only ones left are your favorites and top performers. For lettuce, you can essentially eliminate off-types in one generation through this process so it’s worth putting in the effort. Here’s how that year would go for lettuce:
After your seedlings have sprouted, you should walk through your plot and complete a cycle of roguing when the plants have 4-6 true leaves. At this point you should be paying attention to two main criteria – plant vigour and leaf colour/pattern. It’s always good practice to remove the weakest 10% of seedlings; look for the slowest growers and last to germinate. With 4-6 true leaves showing, you can evaluate the leaf colour and colour pattern. You should be familiar with the varietal norm and make your selections based on this but you can also look for leaves that have colours or patterns unlike the rest of the population and remove them.
Your second walk-through and roguing cycle should be done when the lettuce plants have 10-12 true leaves. At this point, several characteristics can be evaluated to spot off-types – the degrees of lobing, savoying and blistering all contribute to the overall leaf shape. The plant stature, how upright it is and how many leaves are touching or laying on the ground, should be used as another selection criterion. The leaf texture, its thickness and crispness, should also be observed in order to spot and remove off-types. It may be better to wait until closer to plant maturity when evaluating this particular characteristic.
The third roguing cycle should be done when you would normally harvest the lettuce as the criteria at this point are mainly focused on flavour. Select the plants based on sweetness, lack of bitterness or any other distinctive flavours that are characteristics of the variety. You can also select for the degree of heading and tightness of the head.
The last two criteria to select and rogue for are early bolting and disease resistance. Selecting for disease resistance is an ongoing process. Anytime you’re in the field, and certainly during the other roguing cycles, you should remove any plants showing signs of disease. As for selecting for early bolting, caution must be taken with long-season varieties, such as crispheads, not to select so strongly that the variety no longer produces flowers and seeds in shorter growing seasons.
You can see why lettuce is a particularly agreeable crop for roguing and selection. By the time the plants flower, you’ve had a generous amount of time and several growth stages to make observations and selections.
Lettuce is among the easiest vegetables for saving seeds, because it's an annual and it mainly self-pollinates. That means it produces flowers and seeds in one summer, and insects don't tend to carry pollen between flowers, so your saved seeds won't be crossed with nearby varieties.
You should keep your "seed lettuce" at least 20 feet apart from other varieties, just to make sure it doesn't cross, but that distance only matters if the other varieties are allowed to bloom. If you grow other varieties of lettuce just for eating, and you don't let them grow flowers, then you can grow them as close as you want. Allow some of your lettuce plants to grow "too tall", well past the time when they're good to eat. They will grow flower stalks about 4 feet tall, and lots of yellow flowers that look like tiny dandelions. Just like those relatives, the flowers turn into fluffy balls with seeds hidden underneath. You can pick lots of seeds from the fluffy parts when they're dry on the plant: just a few pinches should give you enough to replant a row!
Now for the experienced lettuce grower, here's how you can make your seeds better year after year. While lettuce is mostly self-pollinating, it does happen that a little pollen gets where it shouldn't, so there is always cross pollination. You've probably seen a row of lettuce where the plants all look the same, except for one or two that have a different shape or colour. If you're growing a variety like Jester lettuce that has a little genetic variability, you'll also notice that some of the plants aren't quite what you expect. To save the best seeds, simply be sure to save them from the plants you prefer.