Covering young plants from freezing weather in the Spring - how long?
Last year we planted roses and lilacs so they are very young. With the early warm weather, some people said we should cover them to protect new buds, leaves etc.. We did that last week. Now with predictions of more temperatures below 30 and possible snow over the next few weeks, we are wondering if keeping them covered for weeks at a time without sun will damage them.
Assuming your lilacs and roses are cold-hardy to zone 5, they are equipped to handle cold temperatures and snow. If they haven't broken bud, your biggest worry is the weight of the snow breaking limbs not the temperature.
The problem in Denver, obviously, is the erratic cycle of our temperatures. Warm temperatures cause plants to break bud early, followed by cold temperatures which kill new tender tissue that started to grow. Today's blizzard is a perfect example of cold weather following on warm temperatures: plants don't like that.
Whether you are safe to leave on your plant protection depends on what you used: if the material allows sunlight and water to pass through, you'll be fine. If, on the other hand, you covered them with trash bins or black plastic, you need to remove that when this blizzard passes.