Cold stratification: part 4, springtime

Finally the spring arrives – only in our story about the cold stratification 😊We tried our best sowing and providing the cold stratification.

Is there any guarantee that all seeds will germinate well?
Of course not, hope is good, but kept on the realistic side. Sowing and germinating seeds is not a precise science, and many factors, some out of our control, can contribute to a low germination or no germination at all; reason why keeping your pots for at least another year it is always a good idea.

However, at least some species will germinate, and then you may have to deal with too many seedlings! I always recommend to sow smaller batches of seeds every year, instead of 30 pots at once. And, combine easy germinating species with some of the more difficult ones.

 

What to do when the weather starts to warm up?
I would like to say that we just sit and watch the seeds germinating, but it’s not quite like that 😊

Usually a visible warm up may happen in March in our region, sometimes even later. Not all winters are the same. Unlike the groundhogs, I predict that we will have a very late spring, with short interludes of warm weather here and there.

In case of direct sowing, after the snowmelt, remove the layer of dead leaves/mulch or any other materials you used for extra protection. The best is still to come weather wise, so watch the spot for germination without scratching the ground! In shaded locations it is a good idea to sprinkle a bit of slug pellets around (for just in case).

In case of sowing in moss, there is nothing else to do than waiting for the germination. If too many seedlings appear you will have to transplant some of them later in the season.

In case you sowed in pots, after the snow has melted, open the box(es), or remove any other wrappings from the trays and cold frame to inspect the pots. Most of them will be frozen. Do not worry (follow cold stratification parts 1,2,3); slowly they will start to warm up.

Ideally, boxes and flats with pots should be lifted from the ground on a higher surface to receive more light = warmth. It also makes it easier to keep an eye on them. If March is still very cold, then do this in April.

In case of using a cold frame: open the lid as soon as possible and remove some of the protecting materials. Make a thorough inspection for slugs (eggs can also be at the bottom of pots). Let the lid open as much as possible during warm, sunny days and close it back at night. Most likely you can let go of a part of the wrapping layers.
There is not much to do in the garden so early in the spring. To fuss around the cold frame is a very nice activity 😊 not to mention that early germinating species can take you by surprise.

With the pots buried in the ground there is usually more work to be done as soon as the soil warms up, in case the location is not proper for germination (for example a heavy shaded area). Larger containers are usually to be kept in place; remove the layer of leaves/mulch if it was added and check for slugs; in recent years also cutworms have become a real problem (and they are active at very low temperatures).

If the location is not proper for germination, take the pots out, organize them in a tray/box and lift them up on an elevated surface.
Leaving them buried in the ground, will either delay the germination or expose the fresh, succulent seedlings to various ‘accidents’. Check the bottom of these pots for little slugs or slug eggs; often they hide in between the pots in late fall waiting hungrily for the first ‘victims’. The emerging seedlings can be devoured so fast that it may seem there was no germination at all!

Some species are germinating at low temperatures regardless of the cold stratification method. Depending on the temperatures the first signs of germination are possible in March in our climate even when the pots are looking somewhat ‘frozen’.
From my experience, among the early spring germinators are: Adonis, Corydalis species, Claytonia, Fritillaria, Galanthus, Crocus species, Erythroniums, Hepatica, Helleborus, some species peonies.

How to handle our pots, without a cold frame

If you provided cold stratification underneath your patio table/bench, it is very simple, lift them up. It is not that they can be used for something else until May at least.
A good, not expensive investment it is a small, plastic ‘greenhouse’ with a detachable cover. It is light and can be moved around; when it really warms up, replace the plastic cover with a shade cloth.

I also use a folding plastic table and I recommend it as a good option.
Advantages: they come in various sizes, are easy to move around to the best locations from early spring to summer, you can put the flats underneath when it rains heavily…also they have a very good work-height for transplanting the seedlings later! When you’re done, fold it back and put it away.

During the spring (meaning late May!), be on guard for  heavy rains, late frosts and not to mention late flurries!!! The pots and the emerging seedlings need protection. Keep some plastic sheets/fleece blankets handy.

If you followed the fridge cold/moist stratification, you need to constantly check for signs of germination. Most times not all seeds germinate at once. Wait until a good percentage of seeds have developed radicles and gently plant them in a pot and keep them outdoors if weather allows or at room temperature (it depends when it happens, so you may need indoor lights).

Will all seeds germinate at once?

Many species have a uniform germination. So, after the seedlings grow up a bit, they can be pricked  out, if necessary. * Not all species require pricking out in the first season.
However, other species may germinate gradually over the spring, or over a couple of years (Delphinium fissum, Hepatica, Sanguinaria sometimes, etc.).
In this cases, we believe to be ‘poor germination’, when in fact it is the plant’s mechanism of germinating gradually to give its seedlings better chances of surviving. Wait until you have a few good seedlings to transplant or, keep the pot ‘as is’ until next year.

What happens if species that are actually warm germinators were sown in the fall/winter?

Nothing bad; good seeds should germinate in late spring with the raise of temperature, if they were sown accordingly with their germination requirements.

Before using an indoor lighting system which allows for an early sowing, all species were sown in late fall/early winter and all were overwintered outdoors, either under the snow or in the cold frame. It was never a problem for the usual warm germinating species. Cirsium cannum was overwintered in a tray under snow (shown in the previous post). Other well known warm germinators like Centaurea and Gypsophila species were also sown in late fall with good results.

What to do with the non-germinated pots?

As I mentioned, some species are early germinators at lower temperatures, meaning late February to March, depending on the weather.
From my experience, most other species will germinate between April to early May, in our region. There may be exceptions (Disocorea caucasica for example) but generally speaking if something had not germinated by mid June it won’t happen later in the season. 

Organize these pots and keep them together in a part-shaded spot, or again in a box; redo the labeling. Do not forget to check the moisture throughout the season. By late fall, repeat the cold stratification. Some of the very early spring germinators (like Corydalis, Claytonia, Crocus) become dormant in June, so you can group all these pots together.

As I tried to explain, there are many reasons for failed germination.  Sometimes, seemingly good looking seeds may have internal defects impeding embryo development or germination. When we sow the actual fruits, we cannot even have a visual assessment of the actual seeds.
Some species naturally need repeated cycles of warm/cold, meaning 2-3 years until germination. Not many people are keeping and taking good care of their pots for so long.

However, sowing every year a few pots with a variety of species it is the key of having seeds germinating, seedlings growing and new plants flowering every season!

*Special attention to all species from Aster family: most of them are warm germinators. No matter how you sowed them, they should germinate in the spring. If they don’t, most likely the fruits/seeds were not good: Asteraceae: seeds, achenes and cypsaele

The Germination page has been reorganized with the cold stratification subject listed under Treatments for seeds germination.

Cold stratification: part 1, dormancy
Cold stratification: part 2, FAQ
Cold stratification: part 3, the practicals