Spring is such a roller coaster season in the Truckee Meadows, with cold and warm spells alternating unpredictably (snow tomorrow?). It's hard to predict just the right time to purchase or plant for spring planting. Gardeners and plant sellers alike have to do their best to keep the plants in top condition and get them into the garden at the right time. With experience you will know better when it is safe to plant and when it is too late. For now, here is a guide.
Annuals vs Perennials
Keep in mind that most annuals do not tolerate frost, and transplants will do better if planted into soil that has a bit of time to warm up after that cold winter. Many hardy perennials however can be planted quite early in the spring, especially if they have been kept outdoors at the nursery and are well acclimated to the weather, or if you receive them as bare root plants -- meaning unpotted plants with their roots washed clean. (Perennials can also be planted in the fall with great success.) If you aren't sure, ask your local nursery - Garden Spot Nursery off of West McCarran, or Moana Nursery on... Moana.
You Have Plenty of Time
OK. You live in the Yo-Yo-Weather-Madness Capital of the West. So you have an extended window of time, there is no critical "plant by" day to worry about in the spring although planting should be finished by late spring/early summer - and as a general rule earlier is better.
We tend to want to plant as early as possible, and we see those colorful flowers for sale and can't resist getting started.
But if you transplant too early, you may lose your flowers to frost or a freeze, so be cautious. Some years, planting time runs earlier and some years later, it depends on the weather. Last year we got started a little earlier - this year, not so much.
Caution: Forced Plants
Sometimes both annual and/or perennial plants are shipped in from a warmer area or are forced into active growth and early bloom and sold very early in the season, way too early to plant. This can be difficult for the gardener. Even if the plant is fully hardy in your zone, a forced plant is extremely tender and will be shocked by sudden frost and freezing weather. Sometimes it is better to pass on these lovely but way too premature bloomers. Which leads you to the next item...
Ask Your Nursery
If the plant came out of a warm greenhouse and is fully leafed out, and/or is blooming much earlier than its regular bloom season, and your weather is still freezing or there is still frequent frost, it may be too early to plant it outside. Ask your retailer if it is too early to plant it yet. The big box stores may not have the professional experience the local nursery's I mentioned above might have. Start with the pros first.