SEED SAVING, PROCESSING AND STORAGE PRACTICES
© Frances Michaels
Growing Seed Crops on a Farm Scale
Seed Cleaning and Processing
Seed is an embryo, a tiny package carrying the whole future size, shape and smell of the plant within itself.
Open-pollinated seed is a resource belonging to all people, not a product to be exploited by a few.
Open-pollinated vegetable seeds are genetically diverse treasures that have been passed on from generation
to generation. When you buy and plant open-pollinated seeds you are helping to protect this valuable resource
for the future. The loss of genetic seed diversity facing us today could easily lead to a catastrophe far
beyond our imagining. The Irish potato famine, which led to the death or displacement of two and a half
million people in the 1840s, is an example of what can happen when farmers rely on only a few plant varieties.
"The Food and Agriculture Organization of the United Nations (FAO) reports that 75% of genetic diversity
in food crops was lost in the past century."
From Fatal Harvest, Andrew Kimbrell, Editor.
Why Save Open-Pollinated Seeds?
Open-pollinated seeds can be grown again from seed you save yourself. Saving locally grown seed offers improved
adaptation to local conditions. Local seed can provide food security without dependence on foreign multinationals
using monocultures, pesticides and fungicides to create hybrid seed. It protects the environment from contamination
by agribusiness. It is free of highly toxic chemicals used to store seed commercially. It builds community growth
and communication about the value of seed saving and locally grown food. It can improve links between farmers,
market gardeners and their communities.
What is Hybrid Seed?
Hybrid seed is the result of cross-pollinating two or more different types of a variety to produce another variety.
If seed is saved and planted from this hybrid plant, the germinated seed will generally not grow 'true to type'.
Growing Seed Crops on a Farm Scale
- This is only possible with open-pollinated seed
- Careful attention needs to be paid before sowing on whether the type of vegetable seed e.g. corn, squash
or pumpkins will cross-pollinate with another variety. If cross-pollination is likely this can determine
either the timing or the spacing of the seed crop.
- Seed saving can add another income stream to small farm production as seed is valuable. It saves the cost
of buying seed and may be better adapted to local conditions. Seed saving can also be used to 'value add'
to a crop as over-mature or damaged vegetables can be excellent for seed saving.
Most vegetables are capable of cross-pollinating with another variety of the same type. This is not necessarily
a bad thing as it can lead to a new or improved variety but is undesirable if the seed is expected to be 'true
There are several ways to isolate plants that cross-pollinate to keep the variety pure:
Healthy Plants Produce Healthy Seed
- plant the varieties far enough apart so that their pollen can't reach each other; most vegetables have
a specific distance that two varieties need to be grown apart to prevent cross-pollination occurring
- cover individual flowers with bags after hand pollination
- grow each variety in separate, screened cages
- time plantings so that different varieties are not flowering at the same time so cannot pollinate each
- harvest a seed such as corn from the centre of a large planting
Only save seed from healthy, strong growing plants. It is important to maintain plant care with weeding, watering
and fertilising for the entire life of the plant. Remove any plants that do not appear 'true to type', this is
called 'rogueing'. Do not save seed from any plants that have a suspected virus disease. As seed heads are forming,
the plants need for watering will be reduced. It is usually necessary to support plants so that seed heads do not
fall over in a strong wind. It helps with the seed cleaning and to keep seed free of diseases if the seed does not
contact the soil.
When is Seed Ready to Harvest?
For seed to store well and retain a high viability and an ability to grow healthy, vigorous plants, it needs to be
harvested at the correct time. Seeds should be large and fully mature. Larger seeds have more stored food to nourish
the seeds once they are sown and will produce strong, vigorous seedlings. It is best to harvest dry seed; always try
to avoid getting mature or nearly mature seed wet as this reduces its quality. If rain is expected try to get the
seeds inside quickly for the final drying. Spread the harvested seedheads out on a large sheet or tarpaulin undercover
to continue the drying process. Turn the seedheads over regularly to help the drying process. Air movement is also
helpful. Make sure the seed is clearly labelled as it changes in appearance as it dries and mistakes could be made.
Seed Cleaning and Processing
Once the seed is sufficiently dry it needs to be cleaned. This should happen as soon after harvest as possible.
- removes unviable seed
- removes places for pests to hide
- reduces the risk of disease on the seed
The way seed is cleaned very much depends on the type of seed it is. There are 2 main methods; wet and dry.
This is used for peas, beans, lettuce, corn, radish, carrot, beetroot, silver beet (chard), okra and a wide range
of other herbs and flowers. Bean seedpods, once dry, will often easily break open to release the seeds. Let seeds
mature and dry on the plant as much as possible.
1. Cleaning is done to remove dried capsules, pods and husks by either:
- winnowing - after crushing pods or husks first
- using seed cleaning sieves
- using machinery if available
This is used for tomatoes, cucumbers, melons, pumpkins, squash and other soft fruit.
1. Seed is scooped out, rubbed vigorously and placed in a sieve then washed to remove pulp
2. Seed is then dried for approximately 10 days
3. Further cleaning may be done by winnowing or using sieves
large sieves, an electric fan, large paper bags or sacks.
There are several methods of treating seed: fermentation, heat treatment and freezing.
These first two treatments are done after the initial cleaning, but before seed is dried. Fermentation can
also be used instead of the Wet Method. Freezing can only be done to seed that is fully dried.
This is used to reduce soil-borne diseases; more easily remove gelatinous pulp; and to reduce the germination
inhibitors in the seed coats of vegetables such as tomatoes.
Scoop out the seeds with the pulp that surrounds them, place in a jar and cover with about half as much water
as pulp, place a lid loosely on the jar.
1. Leave to sit at room temperature for a short period depending on type.
2. Usually 24 hours is sufficient for tomatoes.
3. Watch carefully as seeds, particularly of pumpkin and squash, if left fermenting too long will start to
swell and will not be able to be stored successfully.
4. Clean by washing vigorously in a sieve under running water, dry thoroughly.
5. Further cleaning may be done by winnowing or using sieves.
Seeds can transmit diseases from parent plants to the next generation, lowering their productivity. A hot water
seed treatment can control persistent disease problems, particularly with brassica and tomatoes. Treatment times
and temperatures are specific to each vegetable type so care must be taken for the treatment to be effective
without killing the seeds.
The seed needs to be immersed in a large water bath with the temperature maintained evenly for the whole treatment
time. An esky can be used for the water bath as it is insulated. Seed can be tied into muslin bags, pieces of panty
hose or stapled coffee filters. Use waterproof markers to label the seed. Use a thermometer to check the temperature
and then add hot water as needed. Stir regularly. After treatment dry seed as soon as possible.
Broccoli 50°C for 20 minutes to control black rot, bacterial leaf spot, black leg, damping-off, ring spot
Cabbage 52°C for 30 minutes to control black rot, bacterial leaf spot, black leg, damping-off, ring spot
Carrot 50°C for 20 minutes to control Alternaria, bacterial blight
Pumpkin 55°C for 15 minutes to control Fusarium
Tomato 56°C for 30 minutes to control damping-off, bacterial canker, speck and spot
Freezing seeds if done properly does not harm them and can greatly extend their lifespan. All seed banks freeze their
seeds intended for long-term storage. Seed must be fully dried, then seal the seed inside a tightly sealed container,
removing as much air as possible. Freezing can also be used to kill pests that might be present on or in the seeds.
Bean seeds often hide weevil eggs under the skin, freezing them for two days before storing will control most pests.
The most important part of the process is to not open the package or container until you are sure the seeds have
reached room temperature.
Seed Drying for Storage
Dry seed out of direct sunlight in an area with good ventilation. All seed must be sufficiently dry, between 5% and
7% moisture content (by weight) before storing. As an indicator, when sufficiently dry, corn and beans will shatter
when hit with a hammer, squash seeds will break instead of bending, small seeds such as tomato or eggplant will snap
when bent. A simple test to check if seed is dry enough, is to place a small quantity in a glass jar with a lid or in
a plastic bag. Seal it up, place it in a warm place and keep an eye on it for the next few hours. If any moisture appears
on the glass or inside of the plastic bag, the seed is not dry enough and will go mouldy if it is not dried more thoroughly.
In humid areas it can be hard to get seed dry enough, using seed drying beads or silica gel can help the process.
Seed drying beads are modified ceramic materials (aluminium silicates) that absorb water molecules and hold them very
tightly in their microscopic pores. These beads remove water from the air, creating very low humidity inside of closed
containers. Storing seeds inside containers with the drying beads will remove water from the seeds and dry them without
heating. The beads can be reused. Beads and silica gel are used in a similar way by placing them inside the tightly
sealed jars of seed. For silica gel an equal weight in a perforated fabric bag is put with the seed into a well-sealed
jar for 7 to 8 days. After this process remove the silica gel and transfer the seeds quickly into their final storage
In essence, understanding seed quality is understanding that seeds are living, breathing entities. Seeds are in dormant
state and consist of an embryo and a food source. Maintaining seeds at a stable temperature and moisture level will keep
them dormant. If the seed absorbs moisture them hormonal processes kick in to activate life. If it is the wrong time for
this seed to start growing because it is not being planted, some of the seed's stored energy is wasted. If this happens
to the seed repeatedly then seed becomes non-viable.
Most seed has a storage life of approximately 3 to 5 years - some have less than 1 year, such as parsley and onions.
Generally, the thinner the seed coat, the shorter the storage life.
Choose a seed storage container to:
- Keep out rodents and insect pests such as cockroaches and weevils.
- Seal tightly to avoid humidity (moisture) affecting the seed.
- Keep the seeds in the dark
Seed can be stored in a heat-sealed laminated foil bag, a non-permeable plastic bag, a tightly sealed plastic container,
a vacuum sealed bag or a glass jar.
- Avoid using common plastic bags for seed storage by themselves as they are simply too thin and allow too much
air exchange. Inside another tightly sealed container is better.
- Plastic bags that are not gas permeable are available. The best ones are 175 - 250 microns thick; these can also
be heat sealed.
- Fill containers completely with seeds to reduce air space; the less air inside the better.
- If using a container with a screw-top lid use grease or silicon to seal the opening, this will both prevent insects
and air from entering the container.
An ideal temperature for seed storage is 5°C. The best place to store seed containers is a temperature and
humidity-controlled room. The next best choice is a cold room or fridge but the seed needs to be tightly sealed to prevent
moisture-laden air reaching it. The third best choice is a cool, dark cupboard. A combination of vacuum sealing and
refrigeration is excellent but vacuum sealing alone is very effective.
Diatomaceous earth, silica, Pantry Moth traps, vacuum sealer
Seed quality is about two main criteria, viability and purity.
This is a measure of the seed's ability to germinate.
Viability can be impacted by:
- Seed handling
- Exposure to heat and moisture
- Damage by insects or rodents
Varietal purity is a measure of the seed's ability to grow true to type = cultivar (cultivated variety) or variety type.
Physical purity means the seed is properly processed, cleaned and graded. It must be free of contamination with other
vegetable seeds or weed seeds; debris or soil. Any insect-damaged, discoloured or broken seed must be removed.
Labels should include the following information:
Seed germination Trials
- Vegetable name including variety
- Scientific name if known
- Source of seed
- Date of harvest
- Seed batch
This allows you to test the viability of seeds before sowing. Usually 100 seeds are used to give an easy result as a %.
Place the seeds between moist paper towel. Keep the tray at the correct temperature for optimal germination of that
particular seed type. Do not allow the paper towel to dry out. After a few days check for germination.
plastic bags, labels, scales, measuring spoons, funnels.