Scarification - Preparing hard tree seeds for planting

Many trees have seeds with extremely hard coatings. This allows them to remain viable for a long time, waiting for a trigger such as fire or abrasion due to erosion to activate the growing stage. These seeds require some form of scarification to encourage germination.

This is typical of several leguminous, pod bearing tree species such as tagasaste, locust, laburnum, carob etc.

Pre-treating hard seeds with boiling water

The easiest method that I have found works most if the time is to use hot water, almost boiling, water.

1. Boil water
2. Place seeds in a cup or bowl
3. Pour water over the seeds and leave for 12 hours
4. After soaking the water may change colour and the seeds should swell to double or 3 times their original size. For any seeds that do not swell, repeat this process
5. If seeds do not swell up they may require mechanical scarification, see below
6. Plant swollen seeds in suitable growing medium at least seed diameter deep. Many of these hard seeded weedy trees grow in poor quality soil. Using rich potting mix can cause seeds and young plants to rot. I usually incorporate a fair quantity of sand into potting mix for these species.
7. Place seeds and young seedling in partial shade and keep soil damp

Mechanical scarification

Sometimes simply soaking seeds in hot water is not enough to crack the seed coating and so physical 'damage' is required.

You can use nail clippers or sand paper to remove a small amount of the seed surface.

Be careful not to remove to much and avoid damage to the soft inner part of the seed.