Randi V.W. Eckel, PhD

March 13, 2014

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Seeds are sprouting!

What is Cold Stratification and how do I do it?

In case you missed our notes on this in December, many native plants seeds are dormant and require some period of cold stratification to grow. In the simplest terms, the seeds need to experience ‘winter’. Sometimes this can be accomplished by putting the dry seed in the refrigerator, but more often they require a period of cold moist conditions. For most of the country, there is still plenty of time to cold stratify most seed outdoors but you can also use a refrigerator! Simply plant your seed in a pot of moist (not wet) soil, cover with a plastic bag, and put the whole thing in the back of your refrigerator for the prescribed number of weeks. Make sure to 1) mark on your calendar when to take them out and move them to a warm sunny spot and 2) label them well so you remember what’s in the pot and so that no one in your family mistakes them for scary leftovers!

So your seeds are growing – now what?

Seeds need plenty of light and a little fertilizer. If your seeds are getting very tall and skinny – you need better light. Windowsills are often not sufficient. Fluorescent lights work very well – lower the lights to within inches of the seedlings so they get intense light. Fertilize your little seedlings with half strength plant fertilizer (full strength will often burn them at this stage).

Don’t move them from the seed pot too soon!

A common mistake that folks make is they try to divide/transplant their little seedlings when they are too small. Very young seedlings are extremely vulnerable to mechanical damage, disease, and desiccation (drying out). Make sure that your plants have at least one pair of true leaves (not just the often rounded cotyledons or ‘seed leaves’ that first come out) before trying to divide or transplant them. For most plants it is best to let them get some size before you move them out to the garden.

Make sure to harden off your plants.

What does that mean? Direct sunlight and even wind can be too much for young seedlings that have been grown under artificial light or even on a sunny windowsill. If you have grown your seedlings outdoors all along, or in a cold frame, they will be fine. However, if you have been growing them indoors you need to introduce them to the great outdoors gradually. Put them out for a couple hours of indirect sunlight or early morning/late afternoon sunlight for a week or so before planting them out to the great outdoors. Make sure they have enough moisture (but not too much!) during this period so they don’t dry out.

Protect them from freezing temperatures.

Yes, the plants we sell are virtually all perennials, but that doesn’t mean the seedlings you started indoors can handle freezing temperatures when they are tiny! Dave’s Garden has got a lookup for your frost free dates. Don’t plant your seedlings outside until after that date. On the other hand, if you have started your seeds outdoors, you will find many seeds will come up well before the frost free date – that’s OK, they know what they’re doing. I would only protect them with a cover if you get a particularly nasty cold snap late in the spring.

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