The concept of baggie sowing was introduced to me via the site www.robsplants.com. I've been using it for years with great success, but the idea is new. Not all species/varieties can be germinated via this mode, but we're finding many can in our trials.
Baggie sowing is simply placing seed into a resealable plastic bag containing medium instead of using pots. Its a great way to start germinating seed pretty much anytime of the year. You have better control of environmental conditions and you can even speed up the germination cycle for species needing repeated cold/warm stratification cycles. Often I recommend the traditional pot culture germination information in our seed offerings, but occasionally we include baggie sowing information. But still the idea of sowing not using a pot, is too new and folks ask me all the time for details.
Well, here I'm attempting to put the idea to words. Mind you when the seeds have germinated, you have to put them somewhere to continue growing with great vigour so by time spring rolls around, your seedlings are months ahead which means bigger plants and bulbs (corms, rhizomes, etc, etc) at transplant.
Directions: Soak your seed via recommended time duration. Meanwhile, prepare an equal mix of coarse sand and peat moss that is moist, yet easily crumbles in your hand. You shouldn't be able to squeeze water out of it when held tightly in your fist and it should be able to hold its compressed form but crumble when poked. As a general rule the amount of medium you place in a clean resealable baggie is dependent upon seed size. Too much medium and small seed is lost, too little medium for large seed and you're just asking for pain. 1 cup of medium for every 20 medium sized seed such as Asimina, Diospyros, Ziziphus, Cornus, Magnolia, Paeonia, etc. 1 cup for every 5 Gymnocladus, Carya ovata. 3 cups for every 5 Castanea, Carya illinoinensis. 1/4-1/2 cup for every 20 small seeds such as Arisaema, Liliium, Trillium, Paris, Erythronium, Asparagus, etc. Let best judgement guide you. Place medium into LABELED bag (species and date) add seed and gently shake baggie to mix.
When you have the seed mixed in the medium, remove most of the air, roll it up to conserve space and place the roll(s) in a larger (I call it the Master) plastic bag . This acts as double glazing in a greenhouse as it creates a uniform consistent environment (its just a good thing). I then either place the seed bag on my old clunky computer monitor or on the ceramic tiles by the woodstove for gentle warmth (read: warm stratification). If the seed needs cold stratification, its placed in the fridge then brought out when the cold stratification period is over and joins the other bags in the Master bag. I do not recommend it for extremely small seeded species such as Meconopsis nor tomatoes, brassica (kale, broccoli, cabbage, etc). These are better to start en situ.
Alternately, instead of using a peat & coarse sand medium, a coffee filter will do nicely. Just write the variety/species name on the filter before moistening it! Don't use paper towel as it is designed to fall apart and very prone to mold. Soak seed for recommended time, label filter, moisten it, place seed in center and carefully wrap so your precious seed doesn't spill. Place in resealable baggie. Seed that needs light: place seed on side surface of baggie medium and have it facing up.
Baggie sowing is a great way not only to start early, but I'm finding the germination rates are greatly increased because of the ideal consistent environment for germination and the seed tends to germinate quicker. You can get a forest started in a very small space! The only drawback is that once the seed has sprouted, its important for it not to sit there too long as the requirements for germination are not the same for seedling growth. It needs room to grow.