Thursday, January 21, 2010

Wake up Sleepy Seed

On Dormancy and Breaking it

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Ssh: This is all a (hopefully) informative ruse to remind you about wintersown but pretend you didn't read this. Some seed sown outside in the snow.

Since I am stratifying some special Angelica seeds that I just received by mail, I thought it would be fun to write a bit about seeds and dormancy.

In the veggie garden world, we often don't think too much about seed dormancy, because our tomato seeds spring into active growth as soon as we 'add water.' I've seen bean and squash seeds sprouting when still on the vine if left to over-mature in rainy weather. The obligatory nature of most crops is useful to the gardener as it means that the plants will uniformly sprout in a predictable amount of time. If you have tried your hand at starting herbs or perennials from seed, you have probably found that not all plants are as easy-going. Some, like parsley, can take several weeks to sprout. Others, like rosemary, sprout erratically over a long period of time.


Benefits of Variability

It serves us to have our vegetables be reliable germinators, but it doesn't always benefit wild plants to germinate quickly and all at the same time. It makes more sense to have your seedlings sprouting only after certain conditions are met such as undergoing a cold spell, breaking dormancy when the soil is wet, in a certain temperature range and when exposed to light. This will ensure that plants, for example, emerge in early spring when the tree branches are still bare and lots of light hits the forest floor. Also, if seeds germinate at different times than they might miss the slug mower or unseasonably cold temperature that wipes out the first batch.


Seed Life

The seed coat has to be strong enough to protect the embryo inside, and prevent excessive moisture loss. It is easy for us to think of seeds as not quite alive but it is more accurate to say that they are hibernating. How long the seed can live varies between plant types with some only remaining viable for a couple months and others surviving many years. For example, amoung vegetables, members of the carrot and onion family tend to have shorter lives than those in the cabbage family. Heat, moisture and light may all cause the metabolism of the seed to speed up, shortening its shelf life. This is why most seed is stored in cool/cold, dark, and dry place. Exceptions to this are seed that must remain moist to be viable such as water plants,* or to prevent the seed from going into a deep dormancy that is difficult to break.**


Sprouting Seeds

To get a seed to grow, the embryonic plant needs to be watered. Some seeds readily let in water but others have hard seed coats or are coated in residues designed to stop germination while still inside their wet fruits such as tomatoes. The gelly or coating has to be washed off with sufficient water before the seed can germinate.

Scarification: Sandpapering, nicking or otherwise damaging the seed coat but not the embryo to let in water.
Often a seed coat will be so hard that it has to be damaged in some way to allow water to enter. This can be from being chewed on or from soil grains scratching the seed or some other process that the plant has evolved to rely on. In our home gardens, we deal with seeds that need a bit of help breaking through their seed coats by using sand paper or nicking them with a sharp knife. Soaking them over night in hot water is another trick commonly used with plants such as sweet peas.

Hot Water Treatment: Soaking some seeds in hot water can soften seed coats and remove germination inhibitors.
Just like with other characteristics of many plants such as flower colour, leaf form etc..., seed coat thickness can also be variabile leading to variable germination times. I have had NO luck starting strawberry spinach, Chenopodium capitatum, but had heard that it can self sow freely. So instead, I bought a couple plants and told them to do their thing. Later, when visiting Wild Garden seeds, I discovered that they are known for erratic germination because of variable seed coat thickness. They have worked at domesticating this seed so it has more uniform germination.

Stawberry spinach also has tiny little seeds that should be surface sown as they germinate better when exposed to light. This is true of other common vegetables such as lettuce. How much light, and what kind, a seed is exposed to gives it information such as far from the soil surface they are. Small seeds don't have as much stored energy to grow through the soil which is partly why they are not sown as deeply as larger seed such as beans.

Some seeds require light to germinate so should be surface sown - pressed into the soil surface rather than buried.
The other common requirement is cold treatment or stratification. Not surpringly, this is found in plants that are native to temperate regions that have winter. North american wild flowers, trees, and many cold hardy perennials germinate better when treated this way.

Stratification: Sticking seeds in a moistened medium in a cold place like your fridge for a period of time to simulate winter.

Which brings me back to those special Angelica seeds that I received that are in the fridge pretending to be in wintertime. You might be asking yourself why I have to pretend at all because there is at least a foot of real snow on the ground right now. These are such special seeds that I have also sown some in a pot outside buried in the snow but to hedge my bets the rest are in so-called controlled conditions in my fridge.

Winter-sowing - Wintersown

Which brings me to the real point of this whole post. Any remember to do their winter sowing? This is a great technique made popular by Trudi Davidoff. Using recycled containers, she makes them into little greenhouses in which she pots up seeds and puts them outside in the snow. They stay out there, unattended, until they the hardy little seedlings are ready to be planted out. No lights, no mess, usually no watering or maintenance until warmer weather comes, no hardening off and more space to start other plants inside. People even wintersow tomatoes!


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Red iceberg wintersown lettuce waking up - 2009.

*** More Links ***

* Water plants and seed storage, as well as lots more info on Seed Storage at Mother Earth News
** Ephemeral Seed - info from the Alpines from Seed page

Fun Facts on germinating Carnivorous Plants - a pictorial demonstration of simulating fire
Wintersown.org - the official site
How to stratify seeds by Canadian Gardening
Much More on Seed Dormancy for those that really want to know

8 comments:

Daphne said...

I may do a little wintersowing later in the year (I'm sure I've got lots of winter left still). I'll probably do it just to save room under the lights.

miss m said...

I'm adding native plants to the garden this year. All needed stratification. I put them out this week but like you, am keeping some in the fridge as fallbacks.

I will certainly be wintersowing some of my veggies to free up some space. Doesn't get any simpler than that !

And thx for the information on strawberry spinach. I know not to expect great germination for mine.

Cynthia said...

This is really some good information. Thanks so much for sharing.

Edward said...

I started my daylilies indoors a week ago and there are five sprouts out of 26 seeds...so far. Germination usually runs about 90%. I have 13 more seeds to plant tomorrow. The rest of the lights are taken up by overwintering Coleus.

Ottawa Gardener said...

Edward, I was going to visit your blog / site and couldn't connect.

Miss m, Daphne: Yeah, space saving is one of my primary motivators.

Edward said...

I don't have a proper blog. I mostly use social networking sites like Facebook.com and mydaylilies.com. On photobucket you need to search for me as Edward_Kimball.

Ottawa Gardener said...

I was wondering if it were you Ed.

Do you happen to have some of the more popular Asian edible daylilies in your collection?

Edward said...

I don't have any, specifically edible daylilies. One of the local club members makes daylily syrup but I think it is awful.

I am now up to 8 sprouts from 39 seeds. They are all planted in a plastic shoe box. It will look very lush in a month or so.