30 Seeds You Must Refrigerate to Maximize Germination

The growing season has started, and you are eager to sow your seeds, and keep them warm and cozy, so they will germinate fast? Yes and no! Not all varieties like mild temperatures to start their lives, both for your vegetable yard and your decorative garden! Some actually like cold weather! And if you don’t give it to them, they may never pop their first leaves out of the ground, or they will do it late, or sparingly!

This is called cold stratification: some seeds need low temperatures to germinate.

So, before you sow the wrong veggies, perennials and annuals in the wrong place and at the wrong time, you’d better know which varieties need cold stratification, what it actually is, how it works, and – what can you do if winter is over?

Don’t worry; we are here to explore this counter-intuitive gardening phenomenon. We’ll meet 30 seed varieties that need low temperatures, and what to do to get them to germinate profusely.

Thus, first things first…

Why Do Some Seeds Need Low Temperatures to Germinate? What Is Cold Stratification?

Ok, you know what cold stratification means: some seeds need low temperatures in order to germinate, but why? Doesn’t it sound strange?

The explanation is actually very simple indeed. When do most seeds mature and fall to the ground? In fall, of course! And how can they make sure that they do not germinate straight away? They need to “know” that winter is over, and feel the temperatures rising! This way, they understand that spring has come and it is time to grow.

Ok, this is the reason, it’s a “safety measure” for many seed varieties. But how does it work, you may be curious to know? It’s a cunning chemical trick! In the seed coats, they have chemicals that break down at low temperatures, so, over winter in Nature.

These chemicals also stop the coat from breaking, so, they cannot germinate until winter is over!

Simple but ingenious!

Now you are an expert on cold stratification, what happens when you buy seeds that didn’t spend the winter outdoors, in the soil, but in a storage facility at fairly mild temperatures?

The Solution: How to Make Your Seeds Think That Winter Is Over

If you buy these seeds in fall, you can sow them then, and they will go through their natural cycle (or leave the seed bags in a cold place). But how about if you kept them warm, or if you bought them at the beginning of the season (as most of us do)?

Enter a “new” invention: the refrigerator!

We all have one, and seeds are small; they won’t take up much space, and you’ll still be able to store your groceries in it. Yes, because the fact is that for artificial cold stratification, the temperatures of an average refrigerator are perfectly fine – and this is what we are talking about.

You only need to know a few facts and details.

Three Things You MUST Know to Refrigerate Your Seeds

Now you know that some seeds need to spend time in cold temperatures, but there are 3 key things you need to know to get things right:

• The temperature ranges your seeds need.
• How long they need to stay refrigerated.
• If they need a moist or dry environment during the refrigeration.

In fact, for each seed variety we are going to meet, I will give you these details. Mind you, you can be a bit flexible with the temperature range, a few degrees Fahrenheit or half degree Celsius over or above won’t make a big difference.

But how about the moist or dry environment? How can you get these two techniques right? Let’s see…

Moist and Cold Refrigeration of Seeds: Two Different Techniques

This is a very important point, because if you get it wrong, your seeds won’t germinate – despite spending time in cold temperatures. Let’s see these two techniques, they are not hard…

For moist cold stratification, refrigerate your seeds like this:

• Prepare the moist medium; a cloth, cotton, vermiculite, peat moss, coco coir, saw dust etc.
• Moisten it. The key is in the word – it should be humid, not wet! Use a spray bottle. In case…
• Squeeze out any excessive moisture.
• Mix the seeds with the medium.
• Seal in a zip bag or any similar bag.
• Label the bag.
• Chek weekly, for molds etc.

Instead,for moist cold stratification, refrigerate your seeds like this:

• Make sure the seeds are fully dry.
• Seal them in a plastic bag.
• Label the bag.
• Refrigerate them.
• Check the seeds occasionally.

Now, let’s meet 15 vegetable seed varieties you must refrigerate, then we will see 15 decorative ones…

Vegetable Seed Varieties You Must Refrigerate before You Sow Them

Let’s start with food and your kitchen garden; here are 15 vegetable seed varieties you must refrigerate:

1. Carrot (Daucus carota)

• Temperature range: 33.0 to 40.0°F (0.5 to 4.5°C)
• Refrigeration length: 14 to 28 days
• Moist or dry stratification: moist

2. Lettuce (Lactuca sativa)

• Temperature range: 34.0 to 39.0°F (1.0 to 4.0°C)
• Refrigeration length: 10 to 14 days
• Moist or dry stratification: dry

3. Spinach (Spinacia oleracea)

• Temperature range: 35.0 to 40.0°F (1.5 to 4.5°C)
• Refrigeration length: 14 to 21 days
• Moist or dry stratification: moist

4. Celery (Apium graveolens)

• Temperature range: 32.0 to 37.0°F (0.0 to 3.0°C)
• Refrigeration length: 21 to 28 days
• Moist or dry stratification: moist

5. Parsley (Petroselinum crispum)

• Temperature range: 34.0 to 38.0°F (1.0 to 3.5°C)
• Refrigeration length: 30 to 42 days
• Moist or dry stratification: moist

6. Onion (Allium cepa)

• Temperature range: 32.0 to 36.0°F (0.0 to 2.0°C)
• Refrigeration length: 30 to 60 days
• Moist or dry stratification: moist

7. Beet (Beta vulgaris)

• Temperature range: 33.0 to 38.0°F (0.5 to 3.5°C)
• Refrigeration length: 14 to 28 days
• Moist or dry stratification: moist

8. Cabbage (Brassica oleracea)

• Temperature range: 35.0 to 40.0°F (1.5 to 4.5°C)
• Refrigeration length: 10 to 21 days
• Moist or dry stratification: dry

9. Kale (Brassica oleracea var. sabellica)

• Temperature range: 32.0 to 39.0°F (0.0 to 4.0°C)
• Refrigeration length: 14 to 28 days
• Moist or dry stratification: moist

10. Asparagus (Asparagus officinalis)

• Temperature range: 34.0 to 40.0°F (1.0 to 4.5°C)
• Refrigeration length: 42 to 56 days
• Moist or dry stratification: moist

11. Parsnip (Pastinaca sativa)

• Temperature range: 35.0 to 41.0°F (1.5 to 5.0°C)
• Refrigeration length: 21 to 42 days
• Moist or dry stratification: moist

12. Leek (Allium ampeloprasum)

• Temperature range: 33.0 to 37.0°F (0.5 to 3.0°C)
• Refrigeration length: 30 to 42 days
• Moist or dry stratification: moist

13. Swiss Chard (Beta vulgaris var. cicla)

• Temperature range: 34.0 to 38.0°F (1.0 to 3.5°C)
• Refrigeration length: 14 to 21 days
• Moist or dry stratification: moist

14. Rutabaga (Brassica napobrassica)

• Temperature range: 32.0 to 37.0°F (0.0 to 3.0°C)
• Refrigeration length: 21 to 35 days
• Moist or dry stratification: moist

15. Brussels Sprouts (Brassica oleracea var. gemmifera)

• Temperature range: 35.0 to 40.0°F (1.5 to 4.5°C)
• Refrigeration length: 10 to 21 days
• Moist or dry stratification: dry

Decorative Seed Varieties You Must Refrigerate before You Sow Them

And now, let’s move to your front garden with 15 decorative seed varieties:

1. Lupine (Lupinus perennis)

• Temperature range: 32.0 to 41.0°F (0.0 to 5.0°C)
• Refrigeration length: 28 to 42 days
• Moist or dry stratification: moist

2. Coneflower (Echinacea purpurea)

• Temperature range: 34.0 to 39.0°F (1.0 to 4.0°C)
• Refrigeration length: 30 to 90 days
• Moist or dry stratification: moist

3. Columbine (Aquilegia canadensis)

• Temperature range: 33.0 to 41.0°F (0.5 to 5.0°C)
• Refrigeration length: 21 to 42 days
• Moist or dry stratification: moist

4. Shooting Star (Dodecatheon meadia)

• Temperature range: 34.0 to 39.0°F (1.0 to 4.0°C)
• Refrigeration length: 42 days
• Moist or dry stratification: moist

5. Pasque Flower (Pulsatilla vulgaris)

• Temperature range: 32.0 to 38.0°F (0.0 to 3.5°C)
• Refrigeration length: 42 to 56 days
• Moist or dry stratification: moist

6. Prairie Smoke (Geum triflorum)

• Temperature range: 35.0 to 40.0°F (1.5 to 4.5°C)
• Refrigeration length: 28 to 42 days
• Moist or dry stratification: moist

7. False Indigo (Baptisia australis)

• Temperature range: 33.0 to 39.0°F (0.5 to 4.0°C)
• Refrigeration length: 35 to 42 days
• Moist or dry stratification: moist

8. Joe-Pye Weed (Eutrochium purpureum)

• Temperature range: 34.0 to 40.0°F (1.0 to 4.5°C)
• Refrigeration length: 28 to 56 days
• Moist or dry stratification: moist

9. Butterfly Weed (Asclepias tuberosa)

• Temperature range: 35.0 to 41.0°F (1.5 to 5.0°C)
• Refrigeration length: 30 to 60 days
• Moist or dry stratification: moist

10. Jack-in-the-Pulpit (Arisaema triphyllum)

• Temperature range: 34.0 to 38.0°F (1.0 to 3.5°C)
• Refrigeration length: 60 to 90 days
• Moist or dry stratification: moist

11. Siberian Iris (Iris sibirica)

• Temperature range: 32.0 to 41.0°F (0.0 to 5.0°C)
• Refrigeration length: 56 to 84 days
• Moist or dry stratification: moist

12. Wild Bergamot (Monarda fistulosa)

• Temperature range: 33.0 to 40.0°F (0.5 to 4.5°C)
• Refrigeration length: 30 to 60 days
• Moist or dry stratification: moist

13. Black-Eyed Susan (Rudbeckia hirta)

• Temperature range: 34.0 to 40.0°F (1.0 to 4.5°C)
• Refrigeration length: 30 to 90 days
• Moist or dry stratification: moist

14. Wild Geranium (Geranium maculatum)

• Temperature range: 33.0 to 38.0°F (0.5 to 3.5°C)
• Refrigeration length: 60 days
• Moist or dry stratification: moist

15. New England Aster (Symphyotrichum novae-angliae)

• Temperature range: 32 to 38°F (0.0 to 3.5°C)
• Refrigeration length: 28 to 42 days
• Moist or dry stratification: moist

Cold Stratification: The Key to Seed Germination Success! I feel a bit cold now… Do you? Ok, time for a hot cup of coffee, for us, maybe, but not for your seeds – well, not all at least!