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Seed Stratification and Seed Cleaning

Once you have collected native seed and you are going to store it for any length of time, say until spring, you will need to clean it and then stratify it.
Cleaning is important for three reasons; it prevents decay, removes chemical inhibitors and reduces bulk.
In plants where the seed is contained in a fleshy fruit, cleaning the seed will prevent decay and the growth of mold that may damage the seed if the pulp is left on the seed.    Fruit often contains chemical inhibitors that delay germination, so cleaning the seed will improve germination.  Cleaning also reduces the bulk of seeds that are surrounded by fleshy fruit and removes the seed from the chaff in plants that are housed in capsule, pods or cones.

Cleaning can be done by several methods. Species with a hard seed can be run through a food processor to macerate the fruit and the resulting pulp floated off with water or run through a screen.  Dry seed can be crushed by hand and rubbed over a screen to separate the seed from the chaff.   You can also blow on the seed separating the lighter chaff from the heavier seed.  Seeds that are two soft and would be damaged by running through a food processor can be macerated by hand and the flesh floated off with water. Larger seeds and nuts can simply be separated from  their husk, pod or cap by hand.

After the seed is cleaned it helps to moist stratify the seed.  All seed will benefit from stratification even seed with an impermeable seed coat as stratification will encourage bacteria to break down the seed coating.  Stratification refers to the process of mixing the seed with an equal or larger amount of artificial potting mix, peat moss or even potting soil.  Moisten the stratification medium slightly and then store the seed under fluctuating outside temperatures until ready to plant.  Stratification mimics what occurs in nature and maintains the seed at the proper moisture level for germination.  When the seed is exposed to low outdoor temperatures  the seed receives a chilling period which is necessary to allow germination to take place.  This cold dormancy is present in most temperate plants and prevents the seed from germinating at the wrong time of the year.

A pail full of chokecherry seed ready for cleaning

A food processor used to clean seed. Dull blade slightly to puree pulp but not damage seed.

Seed after processing

Chokecherry seed after running through food processor ready to be cleaned. Float off pulp and pour seed and pulp through a screen to separate the pulp and skins from sound seed.
Rinse several times until seed is free of most pulp and skins. Then stratify seed by mixing with peat moss.

False solomon seal seed ready for cleaning in food processor. Run for a few seconds or until pulp and skins are removed.

False solomon seal seed after processing, ready to be cleaned. Pour puree into a pail with water then float off the pulp and skins, leaving the sound seed behind.

False solomon seal seed cleaned and ready for stratification.

this page updated February 27th, 2013