• Common Terms
• Simple Germination Techniques
  • Artificial Stratification (The Baggie Method)
  • Container Winter Sowing (Milk Jug Method)
  • Direct Sowing Outdoors
  • Starting Seeds Indoors
• Caring for Seedlings
• Frequently Asked Questions

Common Terms:

Stratification

‘Stratification’ in horticulture is a term that came about when tree farmers planted tree seeds, layering them in soil during the fall and winter so the seeds were exposed to the elements and experienced the natural cold and moisture of the season. They would then germinate when temperatures warm in the spring.

Many native plants have a natural dormancy period built into their seeds, where the seed undergoes a duration of exposure to the combination of cold and moisture typical of fall and winter in order to germinate. This assures the seeds will germinate in a cooler and wetter time of year (fall or spring) that's most beneficial for their survival to adulthood.

Stratification can be done by sowing seeds outdoors, anytime beginning in fall to late winter, usually in containers or trays with a seed starting mix. When evening temperatures begin to dip below 50°F in the fall is a good indication you can begin to sow.

Cold stratification occurs best at temperatures above freezing, between 33°F and 40°F, and so can be done artificially in the fridge, after which the seeds may be sown after the recommended duration of stratification, or once the seeds begin to germinate in the medium.

Dormancy requirements for some seeds may be more complicated. A ‘simple stratification’ only requires one cycle of cold exposure to overcome dormancy – typical of many perennials. A ‘complex stratification,’ sometimes called ‘complex dormancy,’ refers to seeds that require multiple types of temperature exposures, interchanging between warm and cold over several months – this is typical of ephemerals, native lilies, and several shrubs and trees.

Scarification

To 'scarify' is the weakening or opening of the hard outer seed coat to allow moisture into the seed. Once the hard coat is opened, it permits water to pass through to the inner part of the seed, which can result in the beginning of germination.

In nature, scarification may occur by the repeated freeze-thaw cycle of outdoor temperatures in winter, or when the seed is eaten and passes through the digestive tract of an animal. Or seeds may tumble against sand and stone in a river or stream. The hard coat helps protect the seed embryo, and promotes germination at a time and place beneficial to their survival.

The process of scarifying a seed depends on its size and hardness. Sometimes a hot water treatment is enough, where seeds are soaked in hot (but below boiling) water for 12-24 hours to soften the seed coat. Plants of the legume family (beans and nuts) and the hibiscus (mallow) family can be scarified this way quite easily.

Sometimes a file or sandpaper may be used to scratch the seed coat and expose a bit of the germ inside. More advanced techniques involve using chemicals such as an acid, or even quick exposure to a flame to weaken a seed coat. It is important to note many seeds that need to be scarified also need to be stratified, so scarification needs to come first. In many cases a full outdoor fall and winter exposure results in both conditions being met.

Simple Germination Techniques

Artificial Stratification (The Baggie Method)

This is a popular method of starting seeds indoors using plastic sandwich bags or containers to hold seeds in a moist sterile medium, to be put into a fridge for experiencing stratification. Because it allows for control of the timing of germination, this can get around not having enough days remaining outdoors to get natural stratification, or if you want germination to occur after your last average frost date.

This method often uses a paper towel (A.K.A. the ‘paper towel method’), but we much prefer to use a sterile medium like coarse sand or vermiculite, as we find it safer for handling the delicate seedlings if they begin to germinate, and it’s less conducive to mold growth. For larger seeds, using a seed starting mix as the medium is also fine so long as it is sterile (peat based). 

Please note fine grains of sand or vermiculite have dust which is not healthy to breath in, and should not be handled dry without a respirator or mask, so we moisten the sand/vermiculite in the bag before handling it.

Materials:

• A plastic zip-lock sandwich bag or food container with lid
• A sterile, moisture-retentive medium (we recommend fine vermiculite or a coarse general-purpose sand)
• Seeds (preferably with chaff and stems removed to prevent mold from forming)
• Permanent marker for labeling
• Seed starting soil mix (not garden or potting soil)
• Pots or containers with drainage holes.

Process:

• Lightly dampen the medium so you feel it is moistened, but not soggy
• Mix in seeds, close the bag, and shake it lightly to ensure good contact and distribution through the medium
• Label the bag in permanent marker with the plant name and the date the bag needs to be taken out of the fridge and sown
• Place the bag in a refrigerator (not in the freezer!). Seeds should ideally be kept at temperatures between 33°F and 40°F (average fridge temperatures) for the duration of cold stratification.
• Sow as directed using a seed starting mix into pots or containers.

Maintenance:

Check the bag once every couple of weeks for premature seed sprouting. Some seeds won’t sprout in the fridge without light and warmth, but some might! If they begin to sprout, it’s a sign you should consider sowing the seeds soon. If outdoor temperatures are still getting below freezing, you should slowly acclimate sown seeds to outdoor freezing temperatures, rather than exposing them all at once.

We recommend timing artificial stratification for sowing seeds after the last frost date for your area. Example: if your last average frost date is April 15th, and seeds need 60 days of cold moist stratification, plan to start them in the fridge around or after February 15th. Some species sown artificially outdoors get killed off early from not being acclimated to below freezing temperatures. It’s best to wait to sow them until after the last average frost date.

Container Winter Sowing (The Milk Jug Method)

A method very easy for beginners. This uses a container, such as a milk jug, as a miniature greenhouse to house sown seeds to allow the natural outdoor winter fluctuations to permit stratification. The container protects seeds from birds and animals, drought, wind, and heavy rain. It maintains moisture and increases humidity to promote healthy seedling growth. Furthermore, the seedlings will already be acclimated to the freeze-thaw cycle of outdoor temperatures, and don’t need to be “hardened off,” or acclimated to the cold as if grown indoors. They will germinate at the exactly right time they are supposed to.

A milk jug or bottle is not necessary! It’s just as easy to sow seeds in an uncovered pot with similar results. Cover open pots with a window screen, keep in a protected area, or surround with fencing – to prevent animals from eating the seeds.

Materials:

• Clean translucent milk jugs, water bottles, or plastic containers
• A box cutting knife, X-acto blade, or sharp scissors
• A drill or hot glue gun for making drainage holes
• Standard duct tape
• Seed starting soil mix (not garden or potting soil)
• Permanent marker for labeling.
  

Process:

• Cut the jug in half horizontally, but leave a hinge intact on one side near the handle. If you cut all the way through, you can use a bit of duct tape to make a hinge.
• Poke drainage holes in the bottom of the container. You can use a drill, or (if the plastic is thin enough) use a hot glue gun to melt holes into the bottom.
• Fill the bottom with a few inches of moistened seed starting soil mix.
• Sow the seeds as recommended.
• Tape the jug closed and set it outside in a spot where it will get rain and a little morning sun, but not full sun. Be sure the cap is removed so there is ample airflow!

Maintenance:

Watch for germination starting in March into late June. Some seeds may germinate even later. When seedlings begin to fill up the container, remove the tape and open the hinge. Remove the seedlings, plant up into larger pots or plant out in the garden. Divided and transplanted seedlings should be kept regularly watered until established. Avoid planting out young seedlings in the hottest months of the year, if possible.

Note: new seedlings, once the jug’s lid is removed, should be kept in a partly shaded and slightly cool area, and acclimated over a few days to normal air humidity and higher sun exposure. Doing this too quickly can result in sunburned or dehydrated seedlings. Additionally, when temperatures begin to reach 70°F outdoors, keep still closed jugs out of high sun, or the combination of high humidity and sun can kill seedlings by steaming.

Direct Sowing Outdoors

The method for sowing large quantities of seed over large areas. Useful for meadow plantings or grassland restoration using a native seed mix. Some species prefer to be directly sown, like many annuals and biennials, and legumes with deep taproots (such as Lupine). The downside to direct sowing seeds is lower guarantees of germination, due to seed loss from wind and rain, or consumption by animals. Additionally, seedlings sown directly may take several years before being mature enough to be noticeable in a planting, and may not flower until year 3 or 5 after germinating.

This method relies on the area being cleared of existing vegetation in advance before sowing. Use a sod cutter, or solarize repeatedly with plastic for several weeks or months to kill underlying vegetation, or apply an herbicide to the area before autumn. Failing to remove preexisting lawn/vegetation will result in often very poor germination, as many seeds need light to germinate, and the grass will outcompete seedlings.

We do not recommend cheap “wildflower” or “pollinator” seed mixes easily found commercially, as these often contain non-native species that are usually short lived and don't persist beyond a year or two. Be sure to check the species on the bag before buying. We will happily provide recommendations for bulk native seed mix producers, just ask us!

Process:

• Clear the area of existing lawn, leaves, or weeds
• Scatter seeds over the bare soil in late autumn to early winter (November - January)
• Walk over the area or use a tamper or roller to ensure good seed-to-soil contact.

Optional:

• Mix seed with sand or sawdust before scattering to help with distribution
• Scatter seed just before a snowstorm, or when there is heavy frost on the ground. The freeze-thaw cycle will help work the seed into the soil and press it down.
• Include annuals and short lived perennials such as Rudbeckia hirta, Rudbeckia triloba, or Coreopsis lanceolata for first year blooms. These will persistently seed themselves until perennials grow stronger.
• Include native grasses and sedges in large scale sowings. These help to establish a planting, improve soil over time, and increase root competition to reduce flopping perennials.

Maintenance:

Seedlings will be difficult to differentiate from weeds in year one. Plan to mow the area (on a high setting) at least once or twice the first year to keep weeds back. Perennials will not mind a haircut. You may notice perennials flowering in years 2 - 5 after germination. Monitor the area for invasive weeds that might outcompete young seedlings. If you have an issue with cold season grasses overtaking the area, consider applying a grass-specific herbicide in the spring before warm season grasses emerge.

Starting Seeds Indoors

We do not recommend starting seeds indoors unless you don’t have a choice due to space or early germinating seeds.

In our experience starting native seeds indoors is risky as indoors with low light and low humidity are often not good conditions for germination, and can result in weak seedlings or early die-off. Most seedlings would need a combination of very high artificial light exposure, a balanced moisture (no under or over watering), and higher humidity with gentle airflow. Indoor sowing can promote surface mold growth which may kill off seedlings.

If you don’t have a choice, sow pre-germinating seeds in a container per instructions, and keep the soil moistened, but not soggy. If using a plastic cover, immediately remove once you begin to see seedlings emerge. Use a small fan on a low setting in the room to keep airflow moving to reduce the chances of mold. After the last frost, slowly acclimate young seedlings to full sunlight, by putting them outdoors in shade for a few days, move to part sun for a few days, and so on up to full sun. The more sun they receive, the more watering they will need.

Caring for Seedlings:

Usually when roots are coming out the sown container’s drainage holes, or the seedlings have two sets of true leaves (following their cotyledons – or embryonic leaves), they are strong enough to divide and transplant. Division is optional of course, you may plant the seedlings all together in one pot out into the garden, and the strongest among them will survive just fine, as happens in nature.

Or if you want multiple plants, carefully divide seedlings into larger pots, or plant them out directly in the garden. The younger a plant is, often it is more forgiving for suffering root disturbance.

Divided and transplanted seedlings should be kept in part sun or shade until signs of new growth, and regularly watered until they are established. A favorite idiom of ours to follow for keeping new plants watered is:

Water daily for the first week,

Water weekly for the first month,

Water monthly for the first year.

Generally after one year in the ground, most perennials can handle themselves, except in extreme cases of drought.

The best time for planting out young plants is in the spring and early summer. Second best is in the early fall, anytime before the first frost. Regardless, the earlier the plant gets into the ground, the happier it will be later on.

If you have issues with insect damage, such as aphids, scale bugs, or spider mites, make a solution of a few drops of unscented castile soap (unscented dish soap is fine) and water, and lightly spray all surfaces of the leaves and stems. Repeat treatments for several days.

Frequently Asked Questions

How deep should I sow my seeds? Should they be covered up?

Specific instructions for each species will be included on each packet.

Many seeds require light to germinate, especially tiny to small seeds. The smaller the seed, the more likely it requires light. Dust-like seeds, such as Lobelia, should not be covered, otherwise they won’t germinate. Merely sprinkle the seeds along the surface of pre-moistened seedling soil mix (i.e. surface sow).

Seed with fluffy pappus (Solidago, Liatris) can be surface sown, and these also often require light. In general, almost all seeds don’t need to be covered by soil to germinate, so long as they have good contact with the surface soil and adequate humidity. You can apply a small amount of sand or fine vermiculite as a mulch over seeds.

When should I sow my seeds? Is it too late in the year to sow the seeds I ordered?

Seeds needing stratification may be sown outdoors anytime beginning in the fall through late winter (November to January). Seeds not needing stratification may be sown in the fall/winter, or once soil temperatures are warm, often with best results being in early to mid spring.

By the end of January, if we haven't sown a seed with 60 or more days requiring cold moist stratification, we artificially stratify them and calculate when to sow them after our area’s last average frost date. You can also wait until next fall to try germinating seeds that need stratification outdoors. If so, store seed packets in a dark, cool, dry place. Any seed we sell dry will be viable for several years so long as it is stored properly.

Should I start my seeds indoors or outdoors?

While not impossible to start seeds indoors (like you would tomato or vegetable seeds), growing native plants from seed indoors can increase risks of early seedling death. Including overwatering or under-watering the young plants, too little light, lack of airflow, and die-off from fungal growth. We find it much easier to grow plants from seed when they are kept outdoors, as they would naturally develop.

My seeds never germinated, what do I do?

If you see no germination by the end of June, the following are possible culprits:

• Seeds may have been buried when they should only be surface sown, needing light to germinate – in which case disturb the soil surface a little bit, and some may still germinate.
  
  
• Seedlings weren’t given enough cold moist stratification – in which case you will need to keep the container protected outside for another year to possibly see germination in the following spring. If outdoor nightly low temperatures are still 50°F and below, cold stratification is still ongoing!! This means some seeds may not germinate until late May or early June. Or if you have room in a fridge, stick the container in there and bring it out after a few more weeks. Germination may occur in 2-3 weeks.
  
  
• Seedlings may have already germinated and been killed off by mold, a strong freeze, a sudden hot day, or the soil was too dry. In which case there was too much moisture (mold), artificially stratified seeds were sown outside too early (freeze), enclosed containers were kept in too much sun (heat), or the seedlings dried out too much and died (not watered enough). In any case, something may have been out of balance.
  
  
• Birds, squirrels and mice sometimes dine on exposed seeds. Be sure open containers are kept in a protected place, or covered with a screen or fencing.
  
  
• The growing medium was too dense and moisture retentive. We highly recommend using a seed starting mix for sowing. These are often sterile and resistant to mold growth. Regular potting or garden soil is not recommended, as it is too heavy in organic matter and poorly draining for many young seedlings, and may cause fungal issues or root rot.