DISCLAIMER: I’ve never actually tried to start seeds this exact way. I’ll update this post when I see how effective it turns out to be.
I’ve found that watering from the bottom keeps the soil evenly moist, uses less water, and disturbs the seeds less. Before I was using some donated peat pots and setting those in a baking tray with water for them to soak it up. That works ok, but they dry out pretty quickly and I’d like to have a method that doesn’t rely on a supply of peat pots.
The idea is that I drill holes in the bottom of the tray that will contain the soil and seedlings and set it in another bus tray holding water and allow the top tray to soak up as much water as it wants from the lower tray and then remove it. If I let it sit in there continually it would likely drown the seedlings. One thing potential issue might be overfilling the bottom tray and having it spill over when I put the top tray in to soak.
I’m starting 2 trays of onions this year. So I drilled 1/4″ holes a couple inches apart in the bottom of 2 trays.
Next I mixed up my seed starting mix. Ideally I would just use some compost, but the pile I set aside for this isn’t finished yet. Instead, I’m using equal parts vermiculite, peat moss, and some “potting” soil that appears to be much more top soil with compost than the fluffy potting soil I’m aiming at.
I used a 1 gallon bucket as a measuring cup. I used 1 bucket of each ingredient and mixed them dry with a rake and broke up the bigger clods of the soil.
Set aside maybe 1/4 of a bucket of the dry mix per tray for covering the seeds later.
Then I stirred in about a gallon of water for those 3 buckets of material and worked it until the mix was saturated. In this case I used melted snow as water, but if you use tap water make sure to let it off gas for a day or more so that no chlorine kills the beneficial microorganisms in the compost.
Then I filled each tray up about 2.5-3″ with the wet seed starting mix.
I repeated for the second tray, but really could have done both at the same time if I’d known how much each tray was going to take.
Next, I labeled the two trays with masking tape and put the variety, type of plant, and the date on it. These seeds are intermediate-day length varieties I’ve had success with here, Bronze D’amposta and Australian Brown.
I tear the tops off and hold the package horizontal so the torn edge makes a wider mouth for the seeds to fall off and then shake it side to side. I feel I get a good distribution this way. I put a packet and a half of each type of seed(~450/seeds per tray). I have another packet and a half remaining of each in case this batch fails I can try again.
I then sprinkled on maybe a 1/4″ of the dry mix I reserved earlier and tried to get break or get rid of any bigger chunks in it before sprinkling.
Next I used a mister and wetted down the dry mix and seeds. I shouldn’t have to water from the top again, but it’s important that you get everything completely wet the first time so that the capillary effect, which soaks up the moisture, will be effective.
Now it’s just a matter of putting them somewhere relatively warm (70-75F is ideal). I’m setting them on my rocket stove’s thermal mass bench which is about 80F right now.
They should germinate in about 2 weeks. I’ll update shortly after that to record how it’s working out.
The onions began germinating in only 4 days! Since that was so far off from the 10-14 day estimate I’d seen in 2 places I looked some more and found that under optimum conditions they can germinate in 4 days, so I guess the temperature on the rocket stove bench was good for them.
It’s now 11 days since I sowed them and I’ve been making sure they get at least indirect sunlight as much as I can. Despite the recent bout of well-below average temperatures the cold frame I set up a few days ago is getting into the 80’s even though the highs have only been in the mid-20’s outside so I’ve been setting the trays out during the sunny part of the day.