Fall Planting Once Ground Is 55°F
Flower bulbs should be planted in the fall that they are received once the ground has cooled down to around 55°F, usually after a killing frost (or two).
Although it is common to see packaged flower bulbs in big box stores and supermarkets by Labor Day, it is too early to plant them in almost all areas of the U.S. In our opinion, bulbs are out on store shelves this early because they are marketed as seasonal products, rather than living, breathing plants with their own life cycles. These stores want flower bulbs on the shelves early so that they can restock the shelves with Halloween and Christmas decorations.
If flower bulbs are planted in warm soil, it confuses them and they may not set down roots. Flower bulbs do everything in response to soil and ambient air temperature. Warm soil tells the bulbs to grow top growth rather than roots. Wasted fall top growth and diminished root growth can result in stunted plant growth and poor flower production.
Narcissus bulbs can benefit from being planted a little bit earlier. They are more willing to set down roots in soil that has cooled down to around 60°F.
If Mother Nature surprises us with more prolonged warm spells in the fall, open the exterior container as well as the interior boxes and store your flower bulbs until the weather cools down. Store the bulbs in a cool, dry spot (50°F to 70°F) with good air circulation and low humidity, away from heat, frost and strong sunlight. Poor storage conditions may cause bulbs to dry out, or to become moldy.
If time slips away from you, and you are unable to plant your bulbs before the ground surface freezes, you could place a black tarp (or cut up black garbage bag) over the surface of the garden, weigh it down with rocks, and hope that the sun's warmth can thaw it enough so you can plant. Tulip bulbs are a bit more forgiving: they may be planted as late as January if there is a mid winter thaw. But after that, the bulbs are likely no longer viable, having been out of the soil, without water or nutrition, since their summer harvest in the Netherlands. Flower bulbs may not be held over from one year to the next.
If the varieties you wish to plant are not hardy for the horticultural zone of the planting site, you may refer to our sections on Horticultural Zone Hardiness (HZ), Flower Bulbs for Warmer Climates or Flower Bulbs for Colder Climates.