Hi Carolyn - thanks for contacting us!

Rabbitbrush can be propagated from seed or from cuttings.

Seeds:

• It's possible that it was too dry in the area your seed was planted last fall, and too cool. See page 2 (under Establishment) of this NRCS Plant Guide than mentions a need for temps over 68F and good moisture for seed germination.  https://www.nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/mtpmcpg9696.pdf.  Many drought-tolerant plants need extra moisture to break seed coats and to get established in the ground before they can handle drought.
• You might try "winter sowing" seeds. Under this method, you plant seeds in covered containers and place them in a sunny spot outside mid-winter.  Containers have drainage holes and soil is moistened and kept damp but not wet. The cover has an opening to regulate heat.  A milk jug cut in half horizontally, several holes cut in the bottom for drainage, soil added + moistened + seeds, then the top taped back on but lid left off. The cold helps break dormancy and seeds sprout as it warms up in the spring (possibly before).   Check out www.wintersown.org for instructions or just Google "winter sowing". NOTE: the website was not working for me today. There is also a Winter Sowers Facebook page.

Cuttings:

• On your existing plant, look at the base for runners coming from the crown of the plant.  If you pull some of these up, there might be roots already attached.  Use pruners to cut off a section of roots with foliage attached.  Trim off all but about 6" of the foliage.  The cutting can then be planted.  Prepare a spot for the cutting but clearing out existing vegetation, digging a shallow hole, and loosening the soil to make it easy for the plant to establish.  Add a layer of mulch/dried leaves/etc. around the planting to protect it for early freezes. Water well, and mark the area so you can find it.  If we have a dry winter, water the new cuttings every month or so.
• If you choose to winter sow seeds, you would plant them in the spring using this same method.

You could hedge your bets and try both methods.  :o)

Good luck, and let us know if you have further questions.

Colorado Master Gardener Clinician Annette