Almost all of the flower bulbs in our collection must be planted in the fall prior to the onset of a real winter. A real winter would be a prolonged, 3-month period of consistently cold temperatures that would enable bulbs to fully form flowers (embryos) within, develop mature root systems and avoid premature top growth. Without a proper winter hibernation, bulbs do not yield fully formed flowers, and are prone to flowering short within the neck of the stem, if they flower at all.
For flower bulbs, the winter is referred to as a period of vernalization, the resting period provided by prolonged, consistent cold temperatures. U.S.D.A horticultural zones help gardeners determine which flower bulbs are good for their gardens based on a range of minimum temperatures (in a nutshell: night time temperatures consistently under 32°F yet above -20°F). Horticultural zones provide us with direction as to whether or not flower bulbs would successfully experience the vernalization and bio-chemical trigger to ensure mature spring flowering.
In order to grow flower bulbs in horticultural zones that are too warm for an adequate period of vernalization, one must create a simulated vernalization period for bulbs by prechilling them. In horticultural zones 8 through 10, most flower bulbs must be prechilled at a dark 35°F to 45°F starting in mid-October for up to 16 weeks. (Because of temperature fluctuations and changing temperature patterns, we encourage gardeners in horticultural zone 7b to prechill their Tulips too.)
Prechilling Flower Bulbs
The best way to prechill flower bulbs is in a dedicated bulb refrigerator. Make sure to let us know that you intend to prechill your bulbs when you place your order with us. We will ship your order to you so that you may begin this process in mid-October.
Open your order when you receive it. Remove the inner boxes and bags from the cartons. Keep the inner boxes opened for air circulation. The refrigerator should be a dark 35°F to 45°F without the presence of apples or pears that emit ethylene gas: it encourages flower bulbs to decompose and can damage embryonic flower formation. Never put flower bulbs in the freezer.
In a nutshell, flower bulbs should be prechilled for ten to 16 weeks depending on the variety. Before removing the bulbs from refrigeration, prepare the planting site fully. Remove only the bulbs needed for immediate planting. Do not remove them from the refrigerator and leave them out in the sun in advance of planting. They could lose their cool. It’s alright to prechill the bulbs a little longer than specified, but never shorter.
Select a planting site with partial or dappled sunlight and plant them at least as deep as specified to prolong the bloom period. Apply a light 2” layer of mulch to help retain moisture and to trap cool temperatures in the soil. If rain is insufficient, give them a little drink after planting. Treat the bulbs as annuals.
Flower Bulbs Best Chilled for Warmer Zones
Here is a brief summary of the flower bulbs best-suited for prechilling and planting in horticultural zones 8 through 10.
Tulips should be prechilled for ten to 14 weeks. Never less! The very best Tulips to prechill and plant in horticultural zones 8-10 are:
*Species Tulips Tulipa bakeri Lilac Wonder, T. clusiana Lady Jane, T. clusiana var. chrysantha, T. clusiana var. chrysantha Tubergen’s Gem, T. linifolia, T. orphanidea flava, T. saxatilis and T. sylvestris
*Single Early Tulip Flair
*Giant Darwin Hybrid Tulips
*Parrot Tulips Blue Parrot and Flaming Parrot
*Triumph Tulip Negrita
*Peony Flowering Tulip Angelique
*Fringed Tulip Burgundy Lace
*Lily Flowering Tulips Mariette, Purple Dream and White Triumphator
*Single Late Tulips Avignon, Belle du Monde, Big Brother, Blushing Beauty, Blushing Lady, Camargue, Dordogne, El Niño, Françoise, Hocus Pocus, La Courtine, Maureen, Menton, Queen of the Night, Renown, Temple of Beauty, Yosemite, The Scheepers Hybrid Tulip Mixture and The Tall Sherbet Tulip Mixture
Generally, Narcissi should be prechilled for 16 weeks. Here are some of the varieties that are known to perform best prechilled and planted in horticultural zones 8 through 10.
*Trumpet Daffodil King Alfred
*Large Cupped Narcissus Fortissimo, Fortune, Ice Follies and Pink Charm
*Double Narcissus Cheerfulness, Tahiti and Yellow Cheerfulness
*Triandrus Narcissus Moonlight Sensation, Starlight Sensation, Sunlight Sensation, Thalia and Yellow Ocean
*Cyclamineus Narcissus February Gold and Tete a Tete
*Jonquilla Narcissus Baby Moon, Bell Song, Dickcissel, Hillstar, Pueblo and Sundisc
*Poeticus Narcissus Actaea
*Tazetta Narcissus Avalanche, Cragford, Falconet, Geranium, Golden Dawn, Minnow and Silver Chimes
*Species Miniature Narcissus canaliculatus
*Scheepers Gold Medal Southland Mixture
*Van Engelen's Southland Grand Mix
Miscellaneous BulbsThere is a host of Miscellaneous Bulbs that must be prechilled and planted in horticultural zones 8 through 10. They need to be prechilled for longer periods, perhaps because they are planted more shallowly and are more prone to feeling the immediate heat once planted. These include:
Chionodoxa: prechill for 15 weeks.
Crocus: prechill for 15 weeks.
Eremurus: prechill for 12 to 15 weeks.
Galanthus: prechill for 12 to 15 weeks.
Hyacinth: prechill for 12 to 15 weeks.
Iris reticulata: prechill for 13 to 15 weeks.
Muscari: Prechill for 12 to 15 weeks. The best varieties for prechilling and planting in warm zones include:
*Muscari armeniacum, M. armeniacum Superstar, M. comosum and M. paradoxum
Scilla: prechill for 12 to 15 weeks. The best varieties for prechilling and planting in warm zones include:
*Scilla siberica alba, S. siberica Spring Beauty and S. tubergeniana
Flower Bulbs for Warmer Climates without Prechilling
Some varieties of our flower bulbs may be fall planted without prechilling in horticultural zones 8 through 10. These include:
*Allium cowanii, A. karativiense, A. neapolitanum, A. siculum bulgaricum, A. sphaerocephalon and A. unifolium
*Anemone Giants (Anemone coronaria)
*Iris hollandica (Dutch Iris)
Can We Prechill Bulbs for You?
Sorry to say, but we do not prechill bulbs here for later shipment. Each of our clients must prechill the bulbs themselves. The reason for this is that bulbs can easily lose all of the benefits of prechilling if they are in a delivery truck that travels through a hot area and is not temperature regulated.