35 Seed Varieties that Need Stratification and How & Why It Improves Germination for Seeds Like Lavender

The Rusted Garden Seed and Garden Shop

Have you ever wondered why certain seeds, like lavender, germinate poorly and can take 4 weeks or longer to sprout?  If they even germinate at all. It is because they need to go through stratification. 

Stratification is the natural process of seeds needing a prolonged period of 'cold' to prepare them for germination come warming spring temperatures. The need for stratification is a survival mechanism certain plants developed so fallen seeds stay dormant until the cold of winter passes. Seed are produced when it is warmer, fall to the ground, but won't germinate until the are chilled over a long period. Once chilled, they sit waiting for the warmth of spring. The need for a long period of cold prevents them from germinating early as winter approaches and during periods of overly warm winter days.

Place Your Seeds in the Refrigerator - Stratification

If you don't stratify purchased or collected seeds, they can still germinate but the rate is often much lower and they can actually take 2 or 3 times longer to germinate. A refrigerator is all you need. Most seeds don't need to be stratified. Generally speaking many perennials, that are native to areas with a freezing a winter, benefit from a chilling period. I prepared a list of 35 plants that can benefit from being stratified. These are plants I often seed start indoors.  

There are two ways to stratify seeds. One is called wet and the other is dry. Dry is the only process I do because it is what is most practical when starting seeds indoors. Wet stratification is no more than planting your seeds in a moistened (wet) starting mix and exposing the whole set up to a cold period. That is perfect for greenhouses, cold frames, and places where you can get the right temperatures for the required period of time. I find the dry method to be effective with less work. I just toss them into my refrigerator.

Anise (Hyssop)

Asclepias (Butterfly Weed)

Asparagus

Asters

Bachelor Buttons

Beebalm (Bergamont)

Cantaberry Bells

Catmint

Chamomile

Chives

Columbine

Coneflower (Echinacea)

Delphinium (Larkspar)

False Indigo

Foxglove

Hollyhocks

Joe Pie Weed

Lavender

Lobelia

Lupine

Milkweed

Mint

Oregano

Passionflower

Poppy (Perennial)

Rudbeckia

Sage

Scabosia

St Johns Wort

Strawberry (Wild)

Sunflowers (Perennial Type)

Thyme

Valerian

Vervain (Verbena)

Wormwood

Yarrow

We can artificially create the needed cold period by using a refrigerator. Seed packs or hand collected seed should be placed in the refrigerator for 4-8 weeks. There is no clear information on exactly how long different plant varieties need the cold periods to last for their seeds. The above range seems to be fine. The temperature should be near 32 Fahrenheit or 0 Celsius in theory but most refrigerators are several degrees above freezing and that works. I recommend buying your seeds, that need stratification, several months early, and simply toss the seed packs into the refrigerator. Take them out about 5-7 days before planting them into your seed trays and let them feel the warmth of your home. This process will increase the rate of germination and decrease the time needed for seeds to sprout.

This stratification process can be done on all seeds, in theory. So when in doubt, stratify them in a refrigerator. Check out my seed shop The Rusted Garden Seed & Garden Shop for seeds and all seed starting supplies. And follow me on YT under The Rusted Garden Homestead as I will doing a video series on starting seeds indoors for 2022. I also have plenty of other seed starting videos availble now for viewing.

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