With some daffodils starting to come out months ahead of schedule, many of us are wondering if there is a need to protect our daffodils from the winter if and when it arrives. We contacted Scott Aker, head of horticulture at The United States National Arboretum and asked him about daffodils and cold weather. Thanks for this very interesting and useful information, Scott.
Question: If the daffodils have started to come out, should we cover them?
Answer: It’s not a bad idea to cover flower beds where bulbs are planted with a loose mulch during the winter AFTER the soil has frozen or at least has gotten as cold as it is going to. Loose mulch materials like straw, dry leaves, or boughs of Christmas trees are often used for this purpose. The objective is to insulate the soil from wild fluctuations in temperature. Snow is an even better insulator, but since that is lacking in much of the country, mulch will help to prevent rapid temperature fluctuations that might be harmful. At this point, it would apply to the sprouting foliage mostly, since flower scapes don’t emerge until soil temperatures are much warmer.
In looking at your Facebook page, those who already have blooms seem to be from rather mild regions (Cornwall, Southwest US, and Southeast US), so I don’t think they have to worry about the kind of intense cold that would harm the blossoms. Keep in mind that they only last for a week or two, so they will begin to deteriorate, particularly if the weather is hot or if there is a lot of wind and rain that may damage the blossoms or speed their senescence. A loose mulch may help gardeners in more northerly climates to prolong the life of daffodils that are already in bloom, but there’s not much that can be done if temperatures go below 22-25° — some injury to the blossoms is unavoidable.
Question: If it’s foliage that is showing during these early weeks, will the daffodils probably be OK (sometimes a little frost damage but the flowers will be fine)?
Answer: The tips of the leaves may be yellowed or dried up and brown if we have some really cold weather before spring really arrives, but this usually only affects the very tips of the leaves and the damage is minimal.
Question: Will the foliage bloom only when the temperature reaches a certain level?
Answer: The blooming time is a complex thing that is controlled primarily by temperature—both hours of chilling, and the soil temperature after the bulbs have received sufficient chilling. In the autumn, bulbs grow roots into the soil and then the bulbs must be chilled before they will bloom. Chilling is generally at soil temperatures below 40°F, and bulbs will not bloom at all if they do not receive enough hours of chilling, which is different for each cultivar. On average, fifteen weeks is sufficient. Many bulbs, including most Narcissus, naturally begin to grow leaves before the chilling requirement is met. Generally, the leaves only grow to one or two inches above the soil and remain at this level throughout the rest of the chilling period. The more time in chilling conditions, the faster the development of the flower scapes when soil temperatures do increase in the spring.
Question: If the daffodils have bloomed, are they at risk of damage if the temperature gets down to 25-26 degrees?
Answer: Yes, this is the case if the flowers are fully open. Some cultivars can go to even colder temperatures if they are not fully opened.