Seeds depend on stored food to carry them through dormancy and in order for them to germinate and live as green plants when planted. Seeds that are harvested too early may not have stored enough food or may not have a fully developed embryo. They are also more likely to deteriorate during storage or produce inferior seedlings.
The ways plants produce seeds differs and therefore so do the collecting and cleaning techniques. Seeds can be divided into dry or wet seeds.
- When collecting dry seeds the plant material should have completely dried out in the garden or field or by hanging in mesh bags. Seeds produced in pods are ready when the pods start to yellow and the seeds rattle in the pod. Seeds are usually ripe before the stalks and other plant material dries.
- When collecting wet seeds such as those from tomatoes, capsicums, cucumbers, eggplants, fruit should be just over-ripe (but not rotting) the seeds are scooped out and placed in a container.
- Plants with edible seeds ie. corn, snap beans and soy beans will retain their dry seeds for some time. These plants are usually collected when seed are fully developed, and allowed to cure in mesh bags on mesh trays.
Seeds should be collected (before frost periods) on dry sunny days when the seeds are dry and have no dew or rain on them.
- Dry seeds are removed from the dried seed pods by threshing, smashing or crushing the seeds cases. The seeds are then removed from the crushed material either by hand or using hand screens or winnowed using a fan to blow away lighter material. They are then graded ie. all light weight, discoloured or damaged seeds are removed and discarded and separated from any other material such as weed seeds.
- Wet seeds are removed by cutting the fruit in half and scooping out the seeds and allowing them to air dry before storing. Some wet seeds such as tomatoes are better when fermented. Place seeds covered with pulp and an equal amount of water in a container for about two days mixing twice daily. Mould on top of the mix indicated the fermentation process is complete. Rinse the seeds well in a strainer and dry completely before storing.
All seeds should be dried as soon as possible after harvest and at temperatures ranging between 10-25 degrees Celsius with a relative humidity of 10-20%.
Seeds are alive and like any living thing they can be harmed by adverse conditions. Seeds of some species do not store for very long at all propagation should be done with fresh seed only (this group particularly includes spring ripening seeds of certain temperate zone plants). Most seeds, however, will store for at least 6 months without loss of viability, provided the environmental conditions of their storage are right. Seeds, depending on the species, should be placed in envelopes, bags or airtight jars and labelled with the name and date of collection.
Factors Affecting Storage of Seed
a. Many short lived seeds lose viability if they become dry (eg. Citrus seed only withstand slight drying).
b. Medium to long lived seeds on the other hand need to be dry to survive long periods of storage (4% to 6% moisture level is ideal higher or lower can be detrimental to viability).
c. Fluctuations in moisture levels during storage will reduce longevity (for this reason, seeds keep better in dry climates than in areas of high humidity).
a) Most seeds will store for longer periods at lower temperatures.
b) For seeds not adversely affected by low moisture, each 1% decrease in seed moisture, between 5% and 14% doubles the life of the seed. Each decrease of (9 degrees) Fahrenheit between 32 and 11 degrees F will double the seed storage life.
Types of Seed Storage
- The best storage is in low humidity using airtight containers. However some seeds such as peas and beans prefer some air so are best stored in bags or envelopes; onions, corn, parsley and parsnip can also be stored this way.
- Cold storage in a freezer can extend the lifespan of many seeds as low temperatures will slow down the decaying process, however it will also damage some species. . Seeds need to be returned to room temperature before they are sown.
You may also be interested in....