When is the best time to plant wildflower seed? Spring or Fall?

Question

It is some wildflower iris seeds not bulbs.

Answer 1

Planting in the fall will give them a head start. Virtually any plant that is hardy in the worst weather in your area can have their seeds sown in the autumn. Follow nature. Some seeds, such as pansies (viola) just need to be patted down or the seeds mixed with sand & sown on the soil. Others need to be planted deeper. Most need to be mulched. Some have to be planted early enough (Sept) to allow for good root development before cold weather sets in. Others can be sown later right on the snow.
http://organicgardens.suite101.com/article.cfm/organic_garden_seeds_of_autumn

"Fall plantings should be late enough so that seeds do not germinate until spring. Perennials can also be sown in early fall provided that there are at least 10-12 weeks of growing time before the plants go dormant for the winter. Late fall plantings are advantageous when supplemental irrigation cannot be provided and adequate rainfall is anticipated in the spring. In mild climates, plant during the cooler months of the year, fall through spring, for best results. Fall plantings done prior to periods of rainfall will insure an early display of flowers the following spring."
http://www.bloomingbulb.com/PlantingInstructions.asp?cboGroupID=48&bulb=Bulk+Seed

Iris is one of the seeds that require stratification (a period of cold to break dormancy and encourage them to germinate.) & may take a long time to germinate.

Other plants that require straitification include:
Anemone, Clematis, Corydalis, Dictamnus, Eremurus, Eryngium, Hebe, Helleborus, Muscari, Nomocharis, Saxifraga
This site gives more details on autumn/winter sowing:
http://www.theseedsite.co.uk/wintersowing.html

If you want to wait til spring, the seeds that are stratified can remain safely in a vegetable crisper for a long time, at least until all danger of frost is past in your area if you intend to plant directly in the garden in the spring.
http://www.cdn-iris.ca/seeds.html

In the fall, you can also plant seeds in 6-inch pots, using a combination of leaf mold and peat moss. Cover seeds with 1/2 inch of same material. Any good potting soil that's acidic is good for seed germination.

After planting, over-winter the pots outdoors in November or December. They will come up in 2-3 months, depending on the weather. Germination increases the second year, because there's always a percentage of hard seeds that won't germinate the first year. Some seeds do not germinate until the second year, to increase the probability for good weather conditions and optimize germination success.
Then plant the seedlings in May, when the young plants are usually 3 to 6 inches tall or even taller. Plants usually require watering the first year while roots are being established & will begin to bloom by their second year if growth has been continuous.

"Direct seeding is possible in places that can be left undisturbed, as among shrubs, or among low perennials where the seedlings can be sheltered. If planting seeds in the ground, autumn is the best time for seeding."
http://www.gardenguides.com/plants/plantguides/flowers/plantguide.asp?symbol=IRMA

Good luck! Hope this helps.

Answer 2

Spring. It gives them a chance to grow good roots before winter. You could probably plant in the fall too but I don't know your zone or from which zone the seeds came from. That said, Spring is the best bet.
***UPDATE***
I noticed you said Iros seeds and not knowing which kind of Iris I will add this link for bearded Iris seed just in case.
http://home.flash.net/~mindpath/ssis/oneway.htm

Answer 3

Unless the package comes with specific directions for your area, I would sow half the recommended amount now and reseed with the other half in the spring. This covers both possibilities if some seed needs winter chill. If you plant them this spring you may have to wait another year for some seeds to sprout. RScott

Answer 4

late winter when freezing is unlikely to early spring for seeds, bulbs should be planted in late fall.