Cold Stratification for the Total Novice

So, I just got my hands on some lavender seeds and stinging nettle seeds this week. Both of which I need to start ASAP, because I intend to use them as repellent plants (among other uses, but that's the most immediate need). They're going to help me keep the deer away from other plants/trees. In particular, I'm curious to see if I can use the nettles to guard hostas, and lavender to guard my fledgling orchard.

SO..... it's March already, and spring is coiled up, ready to be sprung. How do you guys do your cold stratification?
Sand? Vermiculite? Paper towels? Moist or dry? How many weeks do I actually need?
I'd rather get this kind of advice from permie gardeners than books or impersonal websites. Feel free, also, to share failures along with successes. Was recently reminded that sharing failures can motivate others to keep trying, because we're all still figuring this stuff out.

Also, if you guys think it's too late in the season and I've missed the window... go ahead and tell me, I'd rather not waste seeds/emotional energy.

Hi Saira,

My rather limited experience in cold stratification is two-fold:
Ether
1) I sow seeds in pots in the autumn outdoors in a spot where the chicken can't get to them
or
2) I place seeds in kitchen towel paper, fold+fold+fold, moisten and place in a zip lock bag, write name of plant and date of starting of this process on the bag, place it in the fridge for 4-6 weeks. I also mark the "take it out!" date in my calendar and depending on the business of the day and/or weather I take the ziplock bag out of the fridge on that date or later, and plant the (hopefully germinated) seeds in seed starting soil in pots and place them on a window sill or in a greenhouse to grow.

Good luck!

Many thanks, Nina! Do you find that the paper towels develop any mold problems?

No mold if you're working clean: clean hands, clean seeds, the water, papertowel and seeds also clean. Good luck!

Best luck here has been in a folded paper towel (2 to 4 squares worth folded into 1/4's) wetted completely but not quite soaked in hydrogen peroxide in about a quart zip lock or sandwich size zip lock.(  The hydrogen peroxide greatly reduces mold problems.)  2nd part of mold control is wash the seeds multiple times.  Have had drying problem with really cheap bags so suggest heavier freezer grade or at least solid good sandwich bags not the really cheap ones and not slider type as they always leak.  Seeds just go in the middle of the layers of paper towel.  Standard off the shelf 3%.  Have had mold problems with water but much less with hydrogen peroxide.

Write the date started, variety and any special things method wise on the side of the bag.  For example best luck with apple seed was if they came straight out of the apple and were never allowed to dry on the surface.  Pull, wash and immediately bag.  That way I have a log of things tried to compare.  Now I would add one other thing here.  I have ended up wishing I kept a written log of methods so suggest a seed diary to so decades later you can remember what worked best with a given variety.(better yet start a thread here so we can all share in the information.)

Now for those of us struggling to keep up 2 other suggestions on these zip locks.  1.  Keep them where you can see them so they can't get forgotten and if forgotten you have a chance to see them if they end up germinating in the bag.(ssshhhhh we don't admit such things can happen)  2.  stand the bags vertically so you know the orientation if forgotten.  Most trees push the root down and use the seed shell as the boring head to go up.  But I had at least one variety forgotten that simply pushed the tree up and the root came out of the pod too.  Had a bunch of healthy starts forgotten in the bags and planted them only to have most of them die.  Digging up after the fact found I planted them upside down because they were one the seed stayed put.  Worst case was a batch of seed stratified for about 13 or 14 months.  Opened them to find 3 varieties germinated in the fridge and most died or were too weak to grow when found.  Got 1 successful tree out of about 40 or 50 seeds germinated.(oopsssss)

Now second best method has been simply to stratify on the tree for those that hang onto the seeds well.  Black locust, honey locust, caltapa and ash.  The locusts don't need stratification but only scarification(best luck with boiling water method) but have tried stratification anyway.  Read that the seeds that stayed on the tree thru the winter were more likely to be healthy and fertile on ash though so there are other reasons for this method.  The Caltapa this is the first year tried.  Picked the pods off the tree second Sat. in Jan. The germ rate has been nearly 100%

third best is stratifying in soil.  Have had major mold problems with this method.  Did try watering the soil with hydrogen peroxide and mold was less but still there.  Want to try oven roasting the soil at say 250 degrees(lowest my oven goes) and watering with hydrogen peroxide is the next goal here.

The one I am really struggling with finding a working method is American Linden.  Lots of lessons there but very little success.

PS you need to look up how long seeds need to stratify for each variety.  Some only need weeks and refrigerator temps.  Some need months including some freezing time.   Some need warm stratification times on either end too.  So read the information

Here are the ones I know off the top of my head.

Cottonwood, Aspen is no stratification time.  Those seeds are only good for days to a few weeks and need to be germiated immediately.  Seeds appear late spring or early summer.  One lesson learned here is the early fuzz has almost no seeds in it and the few there are mostly not viable.  You want the fuzz towards the end of the season.  You will see way more period size white, gray or even black dots in it.  If the seed has color and isn't just white they seem to be way more viable.  Planting depth is just barely covered and great care needs to be taken to keep them solidly damp but not wet till you get them rooted.


Apple is a month or two at frig temperatures.  Best luck, seeds fresh out of the apple, washed a couple of times and then into H2O2 paper towel immediately.  Germination rate has radically varied between runs.  One bunch of store bought Gaia was about 95%.  The trees that came out of those apples widely varied right from the start.  About 1/4 were purplish leaves like crab apple.  Leaf shapes and sizes varied widely in the rest.  A batch of local wealthy with no other trees within miles to polinate had far fewer seeds in them and germination rate was about 40% of the good looking seeds.(did let all of those dry for days before planting though trying to control mold so that may have hurt me)  

Ash seeds some will germinate with no strat but doing a month or 2 greatly increases germination rate.  Recent reading suggests the seeds that stay on the tree were healthier and are more likely to be viable.  So that was this years run.  Got seeds from 2 batches of trees.  Germination in previous years of ground fall has been maybe 5%.  This year waiting till Jan and harvesting seed off the tree germination was way better at maybe 40%.

Rose seeds needed 2 to 3 months stratification.  Did that one on the bushes.  birds ate a lot of the hips but not all.

Locust have done some strat on all so not sure here but it sounds like from the written stuff that they need scarification not necessarily stratification.  from reading it is suggest that new soils may not provide the proper bacteria for it to learn to nitrogen fix.  So suggest gathering soil as well as seed from near the tree.

Black walnuts supposed to need months.  So far zero luck on these.  Because they are supposed to develop a tap root sometimes if not transplanted I have been doing deep holes of nutrient rich soil and trying to direct sow.  Have tried everything from dried and cleaned nuts to still husked nuts.  Some of the written information suggests that they may take years to germinate and one article suggest to break the nut shell they need freeze thaw action.

Blue spruce needs 1 to 3 months.  Most tried will germ after a month of cool.  Dry the cones out, put in a paper bag and shake really hard to knock seeds out has been the best for gathering.

Other evergreens look up what they need.  Some actually need to be baked to be viable

Maples the needs vary so look up.  Most need at least a month of stratification.  Silver leaf maple is like cottonwood and does fuzz seed in the spring.  Most of the rest are fall seeders.  Some of the more extreme version need 2 to 3 months of stratifications.  Some a couple of weeks.

Lilac was interesting.  Kept finding seed pods but no seeds late.  Finally got lucky and got to watch. The seed pods are full but green until they frost good.  As soon as they frost and warm up that very day the pods all crack and drop the seeds.  This meant I got to them in the morning still frozen and all the pods were there and intact.  By noon that day nearly all of them were curled back with almost no seed in the open pods.  The ones back far enough into the bushes not to frost did not open This means the seeds fall immediately on being frozen and warmed and are quickly buried by the leaf litter as the frost knocks the leaves off shortly after.  They need a frost cycle to cause the pods to open and at least a month of stratification.  So far best luck is to wait till just before frost, cut clusters of seed heads off and freeze over night.  Put in a warm paper sack to dry and open.  Shake hard to rattle the seeds out and then sort seeds from all the debris.  Had better luck with the soil stratification batch.  Germ rate of the paper towel batch was about 30% and the soil batch was closer to 50%  Biggest mistake here was storing the seeds in a sack as I wasn't ready to put in the fridge.  Had almost a cup of seeds.(they are fairly small seeds) and a mouse found the sack and ate most and scattered most of the rest.  

choke cherry needs both scarification and stratification.  At least a month of strat.  Have tried cracking with pliers, sanding, rock tumbler, grinding, slamming repeatedly on concrete.  Rock tumbler is a total loss as the pits float and the abrasive doesn't do much damage.  A full month in the tumber and I could just barely see the damage.  So far best luck was scrubing the fruit off in a collinder, letting dry a bit and  grinding one pit at time held in pliers mostly thru the shell and immediately starting strat.  About 5%.  Don't know what I am doing wrong here.

Finally American Linden.  Lots learned here but almost no success.  Lesson one needs a pollinator.  Big beautiful tree up country from me but if you crack the shells only about 1 in 200 has a single seed in it and none of those grew.  The normal shell can have 2 seeds in it and most will have at least one.  The directions call for abrading, shelling or acid treatment  but don't say if the goal is just the shell or if the actually seed needs scarification too.  I have tried cracking the shell with pliers, no germinations, shelling without damaging the seed inside(2 germinations out of probably 200 seeds)  These are really tough to shell without damaging the seed.  Best shelling seems to be dry them out so the seed shrinks relative to the shell and pinch along the line from stem to end with pliers and then using 2 probes to pry the shell to get the seed out.  But really low germ rate says that is a poor choice.  Have tried scarifing the seed to scraping, sanding with no luck.  Fall a year ago enountered an article that suggest harvesting the seed when nearly ready to dry but still green and stratifing the still green seeds including some freezing.  Said the germination rate done that way was suppose to be way better.  Didn't say whether to shell the seeds out or do shell and all.  But this last spring a late frost meant no seeds to play with last fall that one is still on my to try list.

At any rate hope this helps.

I put them in a damp cloth and label, throw in a ziplock plastic bag and put them in the freezer door. Take them out in Spring and plant them or winter plant then before the snow has all gone (clear some snow, lay down some defrosted soil, a layer of seeds out of their plastic bags, more soil, put the snow back on top) take a picture and email it to myself with what is in there, so I can search my emails and I get the date and location
I do this with food seeds I am saving as well, and don't bother cleaning them up first -- I am mimicking volunteer seeds in a compost pile

Funny this came up in the dailyish - just brought my flat of highbush cranberry seeds out for their final round of cold strat  I'm offgrid with no refrigerator to use for such things, so I have to rely on mother nature to do it for me. I often plant things I know will be very vigorous direct in the ground in the fall, but that's certainly not going to work for everything.

They were seeded into a bit of garden soil, which had been heavily amended with duck pond "muck" earlier in the year before growing hungry cabbage and brussels sprouts. This was in a cheapo plastic bin from wally world I picked up about 12 years ago now for just this purpose (side note - the trays have had it the last few years and are cracking into pieces...they don't like the UV in sunlight at all! Good investment, but bad material to have breaking to pieces every time you touch it!)

Because highbush cranberry seed has a double dormancy, it's extra tricky. The cranberry was put in the tray october or november sometime and left outdoors in a cool, shady spot for their first round. The tray was then brought in and kept on the RMH bench from Jan 1st to now, watered occasionally as the 80 to 100 degrees F of bottom heat tends to dry out my plants pretty quick. Not it's back outside buried under a pile of snow in a "warm" area so it doesn't freeze up solid right away. When the "warm" area gets too warm, I'll move it to a shady, cool area on the north side of the "shed wrap" to finish the cold stratification. If necessary due to a good solid warm up in the weather coming, I'll pile snow and ice over the tray then put a light colored tarp over it so it can get what cold it needs

I also brought in other cold strats just a couple days ago from the winter cold. Black walnuts, gentian, hazelnuts, elecampane and several other things. Actually lost track of what I planted in the fall. Same process though - seed tray filled with mild garden soil seeded and placed in a cool area for the fall and winter, then "brought in" to warm up. By "brought in", I'm actually bringing them into a half-hoop "hoop house" type sunroom I have attached. I even have a garden bed in the sunroom I keep planted with usually green onions, brassicas and parsley - nothing better than harvesting fresh broccoli florets in your t-shirt while it's still dropping to near zero outside at night in february.

Another side note - some stratification I've done right in the sunroom garden. I accidentally didn't get my pots seeded with apple out in time and many started sprouting. Gets cold enough down at the shadier end near the plastic that they got what they needed for chilling to sprout.

That's my weird way of doing stratification, which just goes to show you need not be a scientist to get it to work. Nature doesn't require fancy paper towels, plastic bags, special sand or any of the other stuff. Cold is cold - with my methods up here in maine, you just have to avoid going so cold it doesn't count anymore

Some of this depends on your grow zone too, in some places its still winter.

Riona Abhainn wrote:Some of this depends on your grow zone too, in some places its still winter.

Very true and that definitely has an impact. In the other half of the world, it's still summer!

Generally speaking, keeping the seeds between 32 and 45 degrees fahrenheit (zero to roughly 7 celsius) will do the trick. Many probably have basements or garages that maintain a low enough temperature leading well into the spring due to cold cement and the like, so that's also an option for some if the outdoor temps are going to be too warm in the short term. A 90 day stratification might be a bit much this time of the year, even up here in the tundra, but depending on sunshine and ambient temps, a 30 or 45 day stratification further down south might work out in a cold corner of the garage. Offgrid people that don't have magical modern conveniences would just have to pray for gloomy weather

I liked this video, and for me that's saying a lot.



Time:  Depends on the length of stratification you need.  Depending on where you are, you probably have time for artificial strat. if you only need 30-45 days.  Some need 60-90, some need alternating heat and cold.

I wouldn't recommend it though - plant an annual mix this year, or just keep one in arrears in case seeds don't sprout, and plan stratification more carefully for next year.  Or stratify a few in soil mixtures in various ways, see what works with this very limited study, and transplant next year.  Depending on how young the orchard is, you may not really want too much fruit anyways, and could perhaps just protect some few fruits individually.

You can also transplant nettle roots fairly easily.  There are plenty of other plants that are deer resistant - https://satinflower.ca/ can search for 'deer' if you're in the PNW.  For repelling deer, lavender aren't going to grow enough this year anyways.

Cook your young hostas btw.

Hi there, my twopenneth?
I appreciate that we baby our beloved plants along and want to give them 100% chance of growing, but my approach is now to sow more than I need directly where I want them to grow. They are stratified by nature. Interestingly, hawthorn eg generally needs a 2 yrs cycle, so patience required. I have had some success freezing the seeds, bringing them out to warm up and freezing again, but I'm a bit scatterbrained and often lose them in the freezer, or forget which is which (no. I've never heard of pen and paper. What's that? 🙈) Plants that are difficult to get rid of eg nettles, don't need any help. Just sow the seeds and protect, transplant a few clumps and let them self sow. I do think we sometimes make life more difficult than it needs to be. Having said that, I'm in northern Europe, which possibly presents less problems for me. You guys are maybe in the US and Canada? so you are the experts in your areas. Blueberries grow easily here. Though I prefer the original wild ones, or Bilberries as we call them here. Scotland gets the coldest temperatures usually and they grow there in the worst conditions. As for trees, notwithstanding that some are easier to grow than others, the forestry commission puts seeds in plastic bags of damp sand, which are overwintered outside in critter proof places. Nature then does what she does best. I appreciate it's probably harder for you.

I just leave the seeds in/ or place in a seed packet, on the freezer door , at least a week some like echinacea all year, and get great germination. For me it's the conditions and requirements at the seeding level that determines the final yield for transplant

Looks like you're asking about lavender specifically. I grew about 3 dozen plants from seed last year with NO stratification! In my studying before, I found a lot of growers saying it was not necessary for lavender and indeed it was not for me.

I filled 6 pack cells with sterilized 1:1:1 Sand, perlite, coir soil mix. Sterilized because lavender seedlings are very mold sensitive. 70-80 degrees with light 16 hrs/day. They sprouted in about 7 days. Keep moist for about one month after sprouting (until roots are established). Pot up at 6 or more leaves.

Saira Ramallo wrote:Many thanks, Nina! Do you find that the paper towels develop any mold problems?

I also do not completely seal the ziplock bag: You are dealing with a live organism: It needs water and air, and a balance between the two.
Hydrogen peroxide will stop a small mold contamination, if addressed early, but it's better not to have contamination in the first place.

Good to know Cécile!

Matt Todd wrote:Looks like you're asking about lavender specifically. I grew about 3 dozen plants from seed last year with NO stratification! In my studying before, I found a lot of growers saying it was not necessary for lavender and indeed it was not for me.

I filled 6 pack cells with sterilized 1:1:1 Sand, perlite, coir soil mix. Sterilized because lavender seedlings are very mold sensitive. 70-80 degrees with light 16 hrs/day. They sprouted in about 7 days. Keep moist for about one month after sprouting (until roots are established). Pot up at 6 or more leaves.

Agreed that they don't (always) require it, but it sure does help with germination. Just a week to a month for lavender helps in a big way. About to start some sempervivum (hens and chicks) which are similar...they don't (always) require it, but it helps. A lot of seeds are like that, and when they don't necessarily require it, that's when planting in a flat and putting in a cool shady place before spring has fully sprung usually works best. Otherwise, best to plant either in the ground in mid-fall or start your flat late fall / early winter so you can control the stratification process.

... again, for those of us on low power, off grid systems (400w panels with a 400AH battery bank here at 45*N and generally cloudy winters!)  If you've got a grid connection and a fridge with the space, that probably works just as well if not better for most things

Tristan Vitali wrote:Funny this came up in the dailyish - just brought my flat of highbush cranberry seeds out for their final round of cold strat  I'm offgrid with no refrigerator to use for such things, so I have to rely on mother nature to do it for me. I often plant things I know will be very vigorous direct in the ground in the fall, but that's certainly not going to work for everything.

They were seeded into a bit of garden soil, which had been heavily amended with duck pond "muck" earlier in the year before growing hungry cabbage and brussels sprouts. This was in a cheapo plastic bin from wally world I picked up about 12 years ago now for just this purpose (side note - the trays have had it the last few years and are cracking into pieces...they don't like the UV in sunlight at all! Good investment, but bad material to have breaking to pieces every time you touch it!)

Because highbush cranberry seed has a double dormancy, it's extra tricky. The cranberry was put in the tray october or november sometime and left outdoors in a cool, shady spot for their first round. The tray was then brought in and kept on the RMH bench from Jan 1st to now, watered occasionally as the 80 to 100 degrees F of bottom heat tends to dry out my plants pretty quick. Not it's back outside buried under a pile of snow in a "warm" area so it doesn't freeze up solid right away. When the "warm" area gets too warm, I'll move it to a shady, cool area on the north side of the "shed wrap" to finish the cold stratification. If necessary due to a good solid warm up in the weather coming, I'll pile snow and ice over the tray then put a light colored tarp over it so it can get what cold it needs

I also brought in other cold strats just a couple days ago from the winter cold. Black walnuts, gentian, hazelnuts, elecampane and several other things. Actually lost track of what I planted in the fall. Same process though - seed tray filled with mild garden soil seeded and placed in a cool area for the fall and winter, then "brought in" to warm up. By "brought in", I'm actually bringing them into a half-hoop "hoop house" type sunroom I have attached. I even have a garden bed in the sunroom I keep planted with usually green onions, brassicas and parsley - nothing better than harvesting fresh broccoli florets in your t-shirt while it's still dropping to near zero outside at night in february.

Another side note - some stratification I've done right in the sunroom garden. I accidentally didn't get my pots seeded with apple out in time and many started sprouting. Gets cold enough down at the shadier end near the plastic that they got what they needed for chilling to sprout.

That's my weird way of doing stratification, which just goes to show you need not be a scientist to get it to work. Nature doesn't require fancy paper towels, plastic bags, special sand or any of the other stuff. Cold is cold - with my methods up here in maine, you just have to avoid going so cold it doesn't count anymore

I successfully stratified high bush cranberry using mother nature and patience. I packed my seed in a plastic bag with moist sand and buried it in a (well-marked) hole in the garden for two winters. Dug it up the second spring to excellent germination. The only challenge was that I was a little slow in the spring and I had to tease all the little sprouts apart before planting them.

I used the same method (for a single year) with hazelnuts to excellent results.