Protection Bulbs during the winter
Some hardy bulbs such as Daffodils (Narcissi) may suffer damage from severe frost if they are planted late in beds or borders. They should therefore be planted as early as obtainable or be covered with 45 in. of straw, salt marsh hay, leaves, branches of evergreens or similar material. Hardy bulbs planted in grass sod do not require this protection.
Bulbs that are on the borderline of hardiness in any given region, and even many that are usually regarded as tender, may survive the winter outdoors if they are covered. For nearly hardy kinds, those that are just slightly tender —as, for example, Brodiaea uniflora, the Spring Starflower, in southern New York—a covering 4 -5 in. thick of any of the materials recommended above for hardy bulbs will prove sufficient. For more tender kinds—such as Gladioli and Montbretias, in southern New York—a layer about a foot thick will usually enable them to survive by preventing the frost from striking deeply enough to harm them. Even Dahlias may be kept alive through the winter by this method in regions where they would otherwise surely perish.
When winter covering is used, it is important not to put it into position too early, not until the ground has frozen to a depth of an inch or two, and it should be removed gradually, not all at one time in spring. If put on too early, many winter covering materials attract mice and other rodents that may take up winter quarters under their protection; these are likely to damage the plants. Too early or too rapid removal in spring may result in severe damage to tender shoots by sun, wind and late frost.