Growing native seedlings plugs & cold-stratification


Hi Mark,

Regarding growing in plugs & the cold-stratification of forbs/grasses/sedges:

I was considering buying trays of 38 plugs (20" x 10" trays), instead of open bed trays (20" x 10"s), because: 1. it will be easier to divide the seedlings for planting later on, as their lateral roots will become entwined; 2. I should have enough seed to fill 38 plugs, in most cases, and only need 24 of the 38 plugs to be successful in producing developing seedlings. Should I get a open bed trays -- having no individual plugs? The benefit of this solution would be that when I lay the trays on the ground, flushed against each other, I will not have to do as I would have to with the plug-trays; which is to make certain that the plug-trays have enough leaf mould, peat, garden soil, and perilte mix underthem... I want to make sure that the trays are embedded in substrate for moisture retention, and to give some place for the fine root hairs to travel into.

Secondly, in USDA zone 6b/7a NJ, can I sow the seeds into the trays in the fall, leave the trays on the ground (under a shade cloth shield) outside to overwinter and cover the trays with 6" of leaves, then lay and secure burlap above the leaves to make sure the leaves remain as insulation against drought and ambient air temperatures. I'm afraid that the seed would die of freezing; these are all forbs and grasses -- nothing like Asimina, Prunus, or anything that I know wouldn't do well if they freeze.

I didn't have the best success with indoor stratification because it was hard to keep the seed from rotting, without being very careful, because some of the species - those not requiring as much stratification - sprouted too early, and for possibly other unknown reasons; many species worked out, but many didn't as well. I'd like to sow outdoors this fall. I only did that because I ordered seed in winter and was concerned that sowing in winter would have shocked the seed or not allowed enough time for stratification, and that keeping the seed under refrigerated conditions would enable me to extend the winter conditions.

Should I purposely exclude species that do not require stratification (i.e. most of the native grasses I'll sow)? In the refrigerator, they germinated too early when I did that; not sure if that would happen too in late winter/early spring.

I also considered putting each species' seed in a brown paper bag (with garden soil and moistened sphagnum moss) and wrapping all these paper bags (100) in a plastic tarp and placing this in an unheated shed for the winter, protected from the wind and secure from dehydration since they are in a plastic tarp. I prefer this solution if that would work?


Comments (3)
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lycopus(z5 NY)

That could work. I'll share my thought/experience in case it could be of some use to you or anyone else who visits this forum.

One option would be to sow seeds in a small raised bed over the winter and then transplant the seedlings as they come up in the spring into the plug trays or directly where you want them to grow. Personally I like to start seeds in a flat or directly in the garden and then move the seedlings to pots as I get more uniform results that way. When starting the seeds in plugs you can end up with a lot of empty cells if the germination rate is low. With flats you can sow hundreds of seeds and only keep the ones you need. I have had a few species where only 1-5% were viable, so if they had been started in cells or pots it would have been a bust.

Most grasses can be kept dry in the fridge until ready to plant out in the spring or early summer. For some species germination rates may be a little higher if given cold stratification and some like sweet grass require it.

Wrapping them up and putting them in the shed might be problematic if the seeds start germinating early. I start a lot of native seeds indoors in pots for planting out in the spring. I do the stratification on moistened paper towel placed in little clear plastic bags and put those in the crisper. After 60 days or so I check them occasionally for germination. If the seed is really small it can be difficult to get them off the paper towel but it can be done with a spray bottle onto a white plate (so you can see them). This year I had seeds stratifying through late spring and planted some out directly. Some of the species that prefer full sun perform best if sown directly into the garden.

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Might I suggest winter sowing in plastic containers. I have done native seeds this way for years with much success. For me, much easier and more reliable then stratifying indoors.

There are just a couple that I prepare and put outside in December, like Ohio spiderwort (Tradescantia ohiensis) that need a longer stratification process. Most other I put out in Jan.-Feb. Native grasses I do late February and March.

Last year this provided over 400 native seedlings, this year around 300. More than enough to keep me busy with planting throughout the season. Trying to establish a native prairie.

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Sun loving natives are great via winter sowing. Some of my shade plants, however, seem to take more than one season, so that makes for many containers, some even three years!

This June I broke my elbow, still don't have full use of that arm, so hubbie has had to pot up and plant out many things. He says no more winter sowing. LOL!

Seriously, winter sowing is easy and can provide many plants for little cost. I love to watch for the first signs of germination.

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