The techniques used to harvest seeds will vary from one plant family to another and will depend on the scale of your production. Seeds are collected from two main types of seed crops, both requiring different harvesting and processing methods: dry seeded crops, with seeds enclosed in pods or husks and usually dried in place on the plant; and wet seeded crops, with seeds embedded in the flesh of the fruit. All Solanaceae as well as Cucurbitaceae crops fall into the latter category. When mature, dry seeded crops are usually harvested (gradually or completely) with the help of bags, buckets, or any other recipient big enough to accommodate whole plants and seed stalks. Wet seeded crops are usually harvested when the fruit is physiologically ripe (i.e. cucumbers becoming soft and turning yellow), left to mature further (squashes) or sometimes dry (peppers), by simply scrapping the flesh out of it in jars or bowls using a spoon. For certain crops, horticulturally ripe fruits (i.e. normally ready to be eaten for consumption) are also considered physiologically ripe and are indicative of complete seed maturity.
Note 1: It is often good practice to stop watering the plant a few days before harvesting its seeds. This beneficial stress will force the crop to concentrate all its remaining energy on the ripening of the seeds as a survival mechanism. Allowing the seeds to mature this way will increase their quality as well as viability.
Note 2: When harvesting, keep in mind that seeds of a given species that are bigger tend to produce seedlings that are more vigorous. Saving those seeds will be particularly helpful when constituting and maintaining your stockseed.
When and How to Harvest
The plants left in the garden that are meant to be collected for seeds should be labeled accordingly to facilitate the harvesting process. The best time to collect seeds from the selected plants is in the mid-morning or mid-afternoon on a sunny, dry day. Plant bearing seedpods such as brassicas or beans will benefit from being harvested early in the morning when the dew is still on as it will help to prevent the pods from shattering easily. They can then be left to dry and threshed in the afternoon. Vegetable seeds typically reach their peak viability and vigor when they are left on the plant until they reach their maximum dryness. Several indicators can be used to assess the maturity of a seed: its color (beige, yellow, brown, or black depending on the species and variety), the dryness of its content (starchy instead of milky, leaving no marks when the seed is bitten), its ability to shatter easily (in the case of seedpods), sound (seeds rattling inside the pods), or the ease of detachment from the flower stalk. For plants with seedpods that shatter easily, a bag can be put over the top of the plant or flower stalk when all the pods are 60-80% or fully dried. The whole plant is then pulled or cut off, left inside the bag to be dried further, and placed or hung upside down in a non-humid, ventilated place until all the seeds have matured. Note that drying entire plants with their roots generally tends to allow the seeds to better ripen, as the plants will allocate its energy to seed maturation. In crops with indeterminate flowering (i.e., brassicas), seeds do not mature all at once, and for numerous dry seeded crops, the span between the first ripe seed and the last ripe seed can be as long as 4-8 weeks. The highest-quality seeds can then be collected gradually as they ripen by doing several harvests spread over time. Alternatively, the plants can be cut and windrowed outside onto landscape or geotextile fabric for several days for final maturation and curing of the seeds before threshing, provided the weather permits it. It is important to turn the plants regularly to ensure an even drying and for the fabric to be porous in order to absorb the morning dew as well as any precipitations that may occur during this period. Using such fabric will also help to retrieve any seeds that have been released due to shattering.
Note: Fruits of plants growing at lower elevations tend to ripen before those at higher elevations. The same goes with plants located on south and west-facing slopes, whose seeds will ripen faster compared to north or east-facing slopes.
External Influencing Factors
Harvesting techniques will need to be adapted accordingly to anticipate or prevent the falling of seeds on the ground, birds and other animals using them as a food source, as well as adverse weather conditions such as rain (or overhead watering) and hard frost that might affect the ripening and quality of the seeds on the crop. Strong winds should equally be taken into consideration as they might lead to seed dispersal on the ground. Those factors might therefore require harvesting earlier (i.e., before the rain) or later than scheduled (at the risk of having seeds that are somewhat over-ripe), further drying plants/flower stalks by hanging them upside down or laying them down on a tarp in a protected and non-humid place until the seeds are ready for processing, or catching falling seeds adequately.
Specific harvesting and processing techniques for each crop are discussed in Module VII.