Seeds of some woody plants have hard impermeable seed coats that are impervious to water. Because water imbibition is a critical first step in seed germination, it is important to soften or break down the seed coats allowing water entry. There are several ways to break down hard seed coats: 1) pouring hot water over seed and soaking for up to 24 hours; 2) mechanical methods such as files or abrasive tools to physically score the seed to allow water entry; 3) chemical seed coat degradation using concentrated acids (sulfuric).
An effective alternative to artificial seed pre-treatment methods is to adopt nature’s approach taking advantage of microbial, physical and chemical processes over time; that is sow the seeds and wait. This is the approach commercial nurseries often adopt. Woody species that have embryo dormancy are sown in the fall whereas those with double dormancy are sown in early summer; both germinate the following spring. This is the method we recommend as it reliable and non-technical.
Acid Scarification Procedure
- Extreme care must be taken when using this procedure as acids are extremely caustic. Wear goggles and protective clothing. If acid comes in contact with skin, wash immediately. IMPORTANT: Use this method only if you have experience and are comfortable working with acids.
- Place the seeds in a large glass container and pour concentrated sulfuric acid over the seeds so they are fully covered. Stir seeds repeatedly with a glass rod for the prescribed time according to species recommendation.
- During soaking periodically remove some seeds, rinse with water and check for seed thickness and cutting seed to examine seed coat.
- After specified time is reached pour acid and seeds through a screen and rinse with cold water for 10 minutes to remove acid.
- Spread seeds on absorbent paper to dry at room temperature, separate so seeds do not clump together.
- Seeds are now ready to sow or can be placed in cold-moist stratification depending on the dormancy involved.