At the end of a season most gardeners will have a number of lettuces going to seed from which they can harvest seeds from.  But to be sure you label your seeds accurately it is better if you chose your healthiest lettuce plants mid season and label them as the plants you are going to collect seeds from.  For more information on this see Labelling Seed Source Plants. 

As lettuce seeds stay true to type and a single lettuce plant produces far more seeds than one gardener can possibly use I generally only harvest seeds from one plant of each lettuce variety.  And as lettuce seeds keep for five years I do not collect seeds from every type of lettuce  that I grow every year.

 When lettuces go to seed they get taller, skinner and heavier at the top as the seed heads fill out.  This makes the plant prone to falling over or the stem breaking, especially during windy weather.  To prevent this it is best if you stake and tie the plants as they mature.

As lettuce seed heads get close to shedding their seeds they get much darker and the plant itself begins to dry out.  If you pick the seed heads too early the seeds will not have matured enough.  Immature seeds are usually a greenish colour and flatter than fully mature ones.  But if you leave the seed heads too long they will start shedding their seeds.  If a strong wind blows up you can lose almost all the seeds in a single day. 

To make sure you don't lose any of your seeds it's best to pick the heads when the seeds have matured but the heads have not fully dried out.  To harvest lettuce seeds cut the stems just below the seed heads.

To make sure my seeds are fully dried I temporary place harvested seed heads in a paper bag or folded newspaper sheet bag which I then hang up in a dry place for another couple of weeks before separating out the seeds. 

You can skip this stage, but If you dry the seed heads in bags before packaging the seeds you can harvest the heads slightly earlier than you would if you harvest and package the seeds at the same time.  If also reduces the risk of the seed becoming over mature and blowing away in the wind.  For more information see the Bag Drying Seed Heads webpage.



Place the dried stalks with their seed heads in a large mixing bowl.  I have found the pressed stainless steel mixing bowls to be the best as they have a wide opening and are very light. 

Draw your closed hand along each stalk to strip the seed heads and then thoroughly crush the heads and stalks with your hands.  While you are doing this pick out the larger plant pieces.  Continue doing this until only seeds and small pieces of dried plant are left.

Swirl the bowl in a circular motion.  Because the seeds are heavier than the small plant pieces the seeds will drop to the bottom while the plant pieces will move to the top.  They will also settle into a compact central cluster.

Tilt the bowl on an angle and steadily blow air from your mouth over the pile of seeds and pieces of dried plant.  As the plant pieces are lighter they will be blown out of the bowl, leaving the seeds in the bowl.

You will not get all of the bits of plant out on the first go so repeat the swirling and blowing process five or six times.  But be careful not to blow too hard as you will blow a lot of the seeds out as well.  You won't get every tiny piece of plant out but you should be able to get the mixture so that at least 95% of it is seed. If there is a lot of fine dust mixed in with the seeds I sometimes tip the seed mix into a fine sieve and shake it a bit, then return the contents to the mixing bowl.  However I usually do not have to do this.

Now all that's left to do is label and package the seeds.  For more information on packaging seeds see Packaging and Storing Seeds.  For more information on labelling see Labelling Seed Packets.