Growing US Wildflowers From Seed

Growing Wildflowers from Seed (Perennials)

Pre Treatment

Not all seeds need any pre-treatment, those that do will be noted on the bottom of this care sheet with the recommended times.  If your seeds need pre-treating, then follow this guidance first, if not skip straight to the Sowing section.

The best form of pre-treatment is to sow the seeds in the autumn/winter in pots in a cold frame or other protected location (away from mice and birds) and to allow the winter cold to do the work for you.  Accepting that this is not always possible, the alternative method involves cold stratification (sometimes referred to as cold moist stratification).  To do this Place the seeds in a plastic bag or covered container.   Label the outside of the container with date and the seeds name.  Add an equal volume of sharp sand, moss or peat.  Add water to moisten and then mix contents.  The seeds should have some excess water the first day so they can absorb all they will.  After 24 hours check the seeds and add more sand, peat, or moss to absorb any excess moisture in the container.  The seeds should be moist not wet as they can drown in too much water.  Store the seed in the refrigerator (not the freezer) for the stated period in the table at the end of the sheet and then sow as below.

Sowing

The seed, whether treated as above or not, now needs to be surface sown either in a prepared outdoor nursery bed or in pots/trays of good seed raising compost.

Surface sow the seeds initially and then cover with a fine layer of the seeding mix, no more than the depth of the seeds themselves.  Buried too deeply the seeds will rot before they   grow.  The best germination temperatures are listed against each type in the list below and these refer to pot/tray sowings indoors in a heated propagator or frame.  Outdoor sowings can be done when the soil can be worked, but in the less controlled environment, the germination will be more erratic and considerably slower than indoor sowings.  That said, the subsequent plants go through less disturbance when planting out, so each method has its merits.

Germination should occur in most species in 4 – 8 weeks, although some take considerably longer – at all times patience is required and once they start to sprout they should be left until no more seedling emergence is observed for about a week or so.

Growing On

These instructions cover the perennial wildflowers, so once the plants are big enough, they will need to be either transplanted as they get crowded or thinned out (the first method is preferable where small batches of seed are involved as the second means throwing away the thinned out seedlings). In all cases it is best to wait till 2 sets of adult leaves are produced before up-rooting anything.

 
Plant out in their final locations in the autumn (fall) of the first year (for an early sowing) or the following spring for any later sowings.

Flowering can be expected from year 2, although some may take an extra year or so.

Genus	Stratification	Germination Temp
Allium	None	70 F
Amberboa	None	70 F
Aster	None	70 F
Balsamorhiza	1 Month at 70 F followed by 1 month Fridge.	50 F
Coreopsis	None	70 F
Dodecatheon	4 weeks	50 F
Echinacea	8 weeks	70 F
Gallardia	None	70 F
Gentiana	1 Month at 70 F followed by 1 month Fridge.	70 F - slow
Gilia	None	70 F - slow
Hibiscus	None	75 F
Helianthus	8 – 12 weeks	70 F – Autumn sowing is best
Ipomoea	None but soak for 24 hours in warm water.	70 F
Iris	1 Month at 70 F followed by 1 month Fridge.	50 F
Liatris	8 weeks	70 F
Lobelia	None	70 F
Lupinus	None but soak in hot water for 24 hours	70 F
Monarda	None	70 F
Oenothera	None	70 F
Papaver	None	70 F
Passiflora	8 – 12 weeks	70 F – Autumn sowing is best
Penstemon	None	45 F – slow (this is min temp)
Ratibida	None	70 F
Rosa	8 – 12 weeks	65 F – Autumn sowing is best
Rudbeckia	None	40 F – slow (this is min temp)
Sanguisorba	None	70 F
Schrankia	None	70 F
Scutellaria	8 weeks	70 F – Autumn sowing is best
Tradescantia	8 weeks	60 F

Remember only those mentioned above need pre-treatment, the rest can just be sown as per the section above – if sown in the open then they will germinate when the temperatures are sufficiently high.  If sown in trays then a minimum temperature of 65 F should be maintained for optimum germination.

Growing Annuals from Seed.

Annuals can be split into 2 groups.

Hardy annuals.

These can be directly sown as soon as the soil temperatures are above 45 F (6 Deg C).  Ensure the area is weed free as these will compete with your seedlings for space and light.  Thin out if the seedlings appear overcrowded.

If earlier flowers are required, sow in a seed tray of seedling compost and place in a temperature above 65 F (may require bottom heat to achieve this).  Prick out when large enough and space out to grow on.  Acclimatise to the outside temperatures about a week before the final planting time, which should be after the last expected frost in your area (even though they are hardy, you have grown them soft).

Half Hardy annuals.

These should be grown indoors at first like the second method for Hardy annuals.  The final acclimatisation should take place over a slightly longer period as these are not as tough as the Hardy annuals.

Biennials.

Although their life cycle takes place in 2 growing years, the length of time between seed and flower is roughly akin to those of annuals growing in one season.   These should be sown in the height of summer and in the early autumn, such that they germinate and grow somewhat in the first year, ready to flower in the early part of the second.  Follow the rules for Hardy annuals (apart from timing).