Is frost bad for bulbs and perennials?
Snow in the spring is welcome. The snow provides great insulation for plants and can protect hardy flowers from frosty temperatures. The moisture provided is a real boost to bulbs and perennials that are ready to emerge. If daffodils and hyacinths are blooming and snow is predicted, cover them with a bucket or similar container so the weight of the snow doesn’t break them. 
What are plants freezing tolerance?
Tolerance to freezing temperatures depends on the plant. Spring bulbs, such as tulips, crocus and daffodils, can tolerate a light frost or temperatures of 29 degrees Fahrenheit. Perennials that emerge early in the spring are rather cold hardy and can also tolerate a light frost.
Which plants tolerate the cold the best?
Pansies, snapdragons, and dusty miller are examples of spring bedding plants that tolerate cold. Young petunias will tolerate some frost. Most new transplants don’t tolerate frost at all so wait to plant them. Plants like impatiens, tomatoes and basil should be planted in late May to June as they don’t tolerate cool weather.
Which plants should I cover to protect from the cold?
If the forecast is for a hard frost, cover perennials and bulbs just to be safe. Plants located close to the house receive some protection and might not need additional protection. Plants on the south side of buildings and south-facing slopes come up earlier in the spring because the location is warmer and therefore are more at risk with a frost.
To delay early spring growth for plants that come up too soon and are susceptible to frost, mulch flower beds in the fall after the ground freezes.
For “Perennials: Winterizing” refer to message number 1020.
For “Organic Mulches” refer to message number 1609.
For more information, see the following Colorado State University GardenNotes:
