Q: When is it too late to plant bulbs?
A: The best route to success with spring flower bulbs is to plant them at the optimum times. Ideally, bulbs should be planted at least six weeks before hard, ground-freezing frost can be expected in your area. The bulbs need time to root and establish themselves. On the other hand, planting bulbs too early can lead to fungus or disease problems. A good rule of thumb is to plant bulbs when the average nighttime temperatures in your area are in the 40- to 50-degree range. At that point the soil temperature should be just perfect for tucking bulbs in for their winter’s rest underground. In colder northern climates, plant in September or October. In warmer climates you may need to plant bulbs in December (or even later).
If you miss planting your bulbs at the optimal time, don’t wait for spring or next fall. Bulbs aren’t like seeds. They won’t survive out of the ground indefinitely. Even if you find an unplanted sack of tulips or daffodils in January or February, plant them and take your chances. No matter what, they’re better off giving it a fighting chance in the ground or a chilled pot than wasting away in the garage or cupboard. Flower bulbs are survivors by nature’s design. Every year stories abound of bulbs that bloom after being planted under the most improbable circumstances.
— The Netherlands Flower Bulb Information Center