Are you having trouble getting perennial flower, herb, and vegetable seeds to grow, even though it’s easy to grow annual vegetables?
I had this happen to me when I first started gardening. I could grow nearly any vegetable from seed. But my seed starting trays of certain herbs would remain totally ungerminated.
I bought four packets of nettle seeds, and I thought I did everything I could to get them to sprout, but it didn’t work.
It took me a while to realize that I was primarily having difficulty with perennial seeds.
Once I discovered cold stratification, my seed starting failures made sense. The internal clocks of the seeds weren’t triggered to sprout from the warm environment I was giving them. They needed a bit of a winter’s chill to orient them first.
You can grow more kinds of plants if you know about cold stratification. The information below will help you get the most out of your garden.
Cold stratification is an essential process for germinating seeds of certain vegetable varieties. By exposing seeds to cold and moist conditions, their dormancy is broken, enabling successful sprouting While some vegetables like tomatoes and peppers despise cold treatment, others thrive with it.
This comprehensive guide will explore popular vegetable seeds needing cold stratification, Understanding these requirements helps gardeners maximize germination rates, Let’s get stratifying!
What is Cold Stratification?
Cold stratification mimics winter conditions, tricking seeds into “thinking” they’ve experienced winter’s chill. This cold period breaks their dormancy so growth can occur.
The process involves:
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Exposing seeds to cold temperatures between 34-40°F for a period of time. This cold duration depends on the vegetable type.
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Keeping seeds moist during the cold treatment. Seeds can be mixed with moist soil or sand and sealed in plastic bags.
By replicating winter’s cold and wetness, seeds physiologically prepare for spring’s arrival and germinate readily when sown.
Top Vegetables Requiring Cold Stratification
Many delicious vegetables need cold stratification before sprouting. Here are common examples:
Arugula
Botanical Name: Eruca sativa
Cold Duration: 5-10 days
Peppery arugula prefers a brief cold period. Refrigerate seeds 5-10 days before planting.
Chives
Botanical Name: Allium schoenoprasum
Cold Duration: 4-6 weeks
Give chive seeds a lengthy chill for 4-6 weeks. Their germination is slow otherwise.
Cilantro
Botanical Name: Coriandrum sativum
Cold Duration: 1-2 weeks
Cilantro needs only a short 1-2 week cold spell. This enhances germination speed.
Kale
Botanical Name: Brassica oleracea
Cold Duration: 3-4 days
A brief 3-4 days’ refrigeration benefits kale seeds. But don’t over-chill them.
Lettuce
Botanical Name: Lactuca sativa
Cold Duration: 5-10 days
Lettuce seeds appreciate 5-10 days of moist refrigeration before planting.
Onions
Botanical Name: Allium cepa
Cold Duration: 4-6 weeks
Onion seeds need a lengthy 4-6 week cold period for best germination.
Peas
Botanical Name: Pisum sativum
Cold Duration: 7-10 days
Give pea seeds 7-10 days of cold, moist stratification for faster sprouting.
Spinach
Botanical Name: Spinacia oleracea
Cold Duration: 7-21 days
Stratify spinach seeds for 7-21 days depending on variety. Moist chilling benefits them.
How to Cold Stratify Vegetable Seeds
Cold stratifying vegetables at home is simple. Just follow these steps:
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Place seeds in sealable plastic bags filled with moist sphagnum peat moss or vermiculite.
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Label bags with seed variety and date.
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Refrigerate bags for the duration needed per vegetable type.
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Check moisture weekly, adding water if needed.
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Remove seeds after the stratification period ends.
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Rinse stratified seeds and plant normally.
The ideal refrigerator temperature for stratification is 34-40°F. Monitor conditions with a thermometer.
The Benefits of Cold Stratification
Why bother cold stratifying vegetables? What benefits does it offer?
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Enhances germination rates – Cold conditioning can double or triple germination percentages.
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Speeds up sprouting – Chilled seeds often emerge faster than unstratified ones.
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Extends planting range – Stratification permits growing cold-needing plants in warmer zones.
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Saves money – With better germination, you need fewer seeds to start plants.
For easiest vegetable gardening, remember to pre-chill seeds needing this extra winter simulation. With cold stratification, your spring plantings will get off to a vigorous start!
The ultimate guide to plants that need to be cold stratified and/or light to germinate
I created the spreadsheets below when I was planning out a large new flower garden. I became frustrated because I had to research the cold stratification needs of each plant individually. It was difficult to keep track of everything.
Since I’m a huge plant nerd, I made a spreadsheet of all the information. I have divided the information up into categories below.
This list of plants that need cold stratification includes:
– the length of time that the seeds need stratification
– if the seeds need light to germinate
– if the seeds need to be scarred before planting
– optimal starting dates for the whole process
Note that these optimal dates are for zone 7-ish. You might need to shift things ahead or behind based on your last frost date.
This information is based on a last frost date of April 21st
The last frost was on March 21, four weeks ago. The next one will be on February 21, eight weeks from now, and the last one will be on February 7.
Hollyhock benefits from cold stratification
List of flower seeds that need cold stratification and/or light to germinate
Increase seed germination rates; check to see if your seeds need cold stratification
How to Cold Stratify Seeds and Why It’s Required For THESE Crops
FAQ
Do any vegetable seeds need cold stratification?
Do all perennial seeds need cold stratification?
Can I skip cold stratification?
What fruits need cold stratification?