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Succulent seed collection, cleaning and storage

Going.Local
Published on November 19th 2020
5
seeds on a table
When the weather is optimal, and the blooms are many, we inevitably end up with a multitude of seed pods. Some are large and beautiful, others are tiny and bursting with seed.
The question is: "How do we harvest seed and what do we need to know to keep them healthy for a good growing season?"

General seed info

Some terms may sound tricky, but they will help you down the line. Here are some for you to start with:
- Primary seed dormancy refers to seeds that go through a rest period until conditions are favourable for germination. 70% of flowering plants exhibit seed dormancy.
- Physical dormancy is when the seed has a fruit or seed capsule that protects it. When the capsule ruptures, the seed is exposed to water and can start to grow.
- Morphological dormancy is seen in seeds that have an embryo develop prior to its emergence. For example the Dutchman's pipe (Aristolochia hamptonii).
A close up of some Aristolochia flowers

Dutchman's Pipes

Aristolochia spp.

- Physiological seed dormancy refers to seeds with a "block" inside the seed that stops it from germinating.
Most commercial varieties are bred to have low seed dormancy, but in some cases, the seeds will need a little push. These can be fluctuations in temperature (like a seasonal change), light or a spike in nitrogen.
How you go about breaking dormancy:
  • Physical dormancy requires chaffing the outer layer with sandpaper or exposing it to a mild acid.
  • Physiological dormancy will require a change in environment (temperature or day length).
  • Morphological will require extended periods of moisture.
seed pods

Seed collecting

Collecting seed is easier to do from your backyard. The best time to do so is just before seed dispersal. Naturally, you may be anxious at the possibility of losing the seeds before you harvest. There is an easy way to get around this:
Tip | Use a stocking or similar thin weave pocket and cover the seed pod when it is developing
Some plants take a year or more to produce seeds. For example, Asclepiads or carrion flowers take 12 months, whilst most mesembs will hold onto the seeds until the first rain. Be aware of this and time your harvest accordingly.
Tip | Seeds can mature after being harvested, in some cases, if it is harvested with the stem and left in a cool dry place.
seed pods

Seed preparation

A common misconception is that all seed undergo a period of desiccation (i.e. drying) before storage. This process is in fact both plant- and seed-dependent. Three types of seeds exist:
  • Orthodox seeds (from arid and Mediterranean environments) are acclimated to desiccation. This means they can tolerate being dried to a 5% moisture content. They can also be stored in a freezer (and should, to prolong their lifespan).
  • Recalcitrant seeds tolerate water loss but to a very limited degree. These seeds do not store well and are harder to germinate.
  • Intermediate seeds also referred to as non-orthodox, can tolerate some drying but not to the extent of orthodox seeds. 15% of angiosperms fall within this category.
When you know what type of seed you have harvested, you can then proceed to prepare it for storage.

Drying seeds

Drying seeds seem like an easy thing to do, but there is a few things to consider when drying at home. Everyone’s ‘home’ is not the same. Humidity and temperature will play an important role in drying your seeds. If they dry too quickly or do not retain enough moisture, it will affect their germination.
Temperature: Harrington’s Thumb Rule states that a seed's ‘lifespan’/longevity is doubled for every 5 degrees Celsius fall in temperature. Storing at lower temperatures is ideal.
If you have high ambient humidity, you might struggle to store seeds long term and visa versa if your climate is too dry you will have the same problem.
seeds in a glass jar
Making use of glass bottles will allow you to see your seeds, but will also expose them to sunlight, therefore keep them in a closed cupboard.

Seed Cleaning

Cleaning is a necessary practice as dead plant material will encourage fungal and other pathogens to infect the seedling mix once sowed.
There are several ways in which to clean seeds:
  • Use Garden Riddle Sieves with different-sized holes.
  • Use air by placing the seed bowl in front of a slow fan and sieve by hand.
See Clint's post of seed cleaning:
These practices replace air-screen separators and gravity separators which are expensive equipment for large scale cleaning.

Seed Storage

Seed viability (how long they last) is species-specific, which means some seeds cannot be stored whereas others can be viable after thousands of years. Consequently, there exists no hard-and-fast rule when it comes to storage.
The best is to understand what may harm your seeds:
  • Heat: The heat generated in a compost heap is often used as a means to kill weed seeds, but it works just as well on any type of seed. If the storage temperature exceeds room temperature (>20 C) it will shorten the lifespan of the seeds.
  • Ideal: Storage at 15 C and 15-20% humidity.
Some options:
If you live in an area with high humidity or where the room temperature can fluctuate drastically, then it might be best to try to keep it in sealed containers. And remember, seeds are a great resource to share. If you are not using it, you can always swap it!
A stack of seed envelopes
Bibliography:
Erickson, T., Barrett, R., Merritt, D., & Dixon, K. (Eds.). (2016). Pilbara seed atlas and field guide: plant restoration in Australia's arid northwest. CSIRO PUBLISHING.
Andersson, L., & Milberg, P. (1998). Variation in seed dormancy among mother plants, populations and years of seed collection. Seed science research, 8(1), 29-38.
Jorgensen, K. R., & Stevens, R. (2004). Seed collection, cleaning, and storage. In: Monsen, Stephen B.; Stevens, Richard; Shaw, Nancy L., comps. Restoring western ranges and wildlands, vol. 3. Gen. Tech. Rep. RMRS-GTR-136-vol-3. Fort Collins, CO: US Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 699-716, 136.
Probert, R., Adams, J., Coneybeer, J., Crawford, A., & Hay, F. (2007). Seed quality for conservation is critically affected by pre-storage factors. Australian Journal of Botany, 55(3), 326-335.

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