After learning more about chilling, you probably want to learn how to cool flowering bulbs. Tulips and narcissus need a 12- to 16-week cooling period before they blossom in the spring. The recommended temperature for chilling bulbs in a refrigerator is around 40 degrees Fahrenheit (4 degrees Celsius). Just be careful not to store them close to any fruit, as the ethylene gas released will lessen bloom. The bulbs should be kept in a vented mesh bag in the refrigerator.
The length of the cold period for bulbs varies depending on the species, but generally speaking, the flowers that emerge earliest, even through snow, require the least amount of chilling time, while those that do so later require the most.
How long can tulip bulbs be stored in the fridge?
The tulip bulbs go through a procedure called prechilling, which involves keeping them between 35 and 48 degrees Fahrenheit for at least 10 weeks and no longer than 14 weeks before planting (but never in the freezer!). When you dig your bulbs after the spring bloom, it’s simple to meet the minimal requirement, but you’ll long exceed the 14-week window before you can replant the bulbs in the late fall.
There are other tricky aspects of keeping your bulbs over the summer. You shouldn’t keep the bulbs in a garage, shed, or basement without temperature control because the cooling temperature needs to be stable with no significant temperature swings.
When you’re ready to plant the bulbs, take them out of their chilly storage. Just a few hours of warming them up will return them to their original, non-chilled state.
Can bulbs be chilled in a refrigerator?
First off, the term “forcing” is inaccurate because it conjures up images of labor. We’re merely deceiving the bulbs into believing that winter is ended much earlier than it actually is. At a time of year when spirits desperately need renewing, forcing is a simple trick that gives the uplifting fragrances and hues of spring. But in order to get the benefits when the snow starts to fall, you must plant now, in the autumn. Although we frequently think of forcing Daffodils, Hyacinths, and Tulips, many of the smaller bulbs, such as Crocus, Muscari (Grape Hyacinth), Scilla, Dwarf Irises, and Anemones, are also incredibly simple and rewarding to force.
There are two categories of forced bulbs: those that need freezing and those that don’t. When bulbs do need cooling, they actually only need a much shorter period of time than a typical northern winter. (For specifics, see the list at the bottom of this entry.)
The bulbs should be planted in any well-draining potting soil, given water, and left for the shortest amount of time (see below) in a cool, but not freezing, dark location. After that, they should be brought indoors where it is warm and well-lit. The bulbs immediately sprout and flower because they believe spring has arrived. That simple—the bulbs handle the bulk of the labor.
If you want to involve your children or grandchildren, this is a terrific project to do with them. The actual planting process can be a little messy, so it’s a good idea to spread some newspapers to catch any dirt that may leak, collect all of your pots in one location, and complete the planting in one go.
If you want to force bulbs, you can use any pot as long as it has three to four inches of space below the bulbs for root growth. Show off your favorite terra cotta pots, flea market purchases, and tag sale finds at this event. You will need to water your bulbs carefully if you choose a pot without a drainage hole in the bottom since bulbs that sit in moist potting mix will quickly decay. If you’re pushing tall Tulips or Daffodils, think about using a ceramic or terra cotta pot. When fully bloomed, these blooms can be top-heavy and may tumble if grown in light plastic pots.
We advise using a soilless potting mix to plant bulbs (available at garden centers and hardware stores). A soilless mixture retains moisture while easily allowing extra water to flow away.
Put potting mix in a plastic bucket or tub before starting to pot the bulbs. Once the mixture is moist but not soggy, gradually add water while stirring. If you want to include a child or grandchild in the excitement, this is the perfect task for a very young assistant. Fill the pot approximately three-quarters full with the moistened mixture. If you can’t determine which end is up, like with Anemone blanda, place the bulbs on their sides rather than root-side down on top of the mixture. The bulbs should be placed considerably closer together than you would in a garden; they practically need to touch. Finally, add more mix. Larger bulbs should be covered up to their necks, leaving the tops of the bulbs exposed. Cover little bulbs entirely with a 1/2 layer of mix. After potting, properly water.
Cold-hardy bulbs must first be stimulated to form new roots by being kept cool and moist for a duration that varies depending on the type of bulb in order to force them into bloom (see listing below). Most bulbs flower best when stored at 40-60F for the first 3–4 weeks after potting, then at 32–40F for the remainder of the cooling period. This transition replicates the fall to winter season’s decrease in soil temperature outdoors.
Placing bulbs outside and letting nature take its course is the simplest approach to get them to cool. Bury the pots in a layer of dry leaves kept in place by a plastic tarp or in a pile of mulch, such as bark or wood chips, and cover the pile to avoid the development of a frozen crust to protect the bulbs from sudden changes in air temperature and from freezing cold. If you’re fortunate enough to have one, you can also chill bulbs in a chilly cellar, an unheated garage, or a cold frame. Just make sure the temperature doesn’t drop below freezing.
Make sure there is no fresh fruit present in the refrigerator before chilling bulbs. Fruit naturally releases ethylene gas as part of the ripening process, and this gas will obstruct the growth of flowers. It could be challenging to set up for the appropriate temperature shift indicated above in places other than a refrigerator. Fortunately, most bulbs haven’t read the instructions, so if the temperature doesn’t fluctuate too much above or below 40F when the bulbs are rooting, they will root wonderfully. Professional growers accurately control the temperatures while filling enormous walk-in coolers with planted bulbs. You may achieve fantastic results using an old refrigerator in a basement without ever touching the temperature settings.
The potential drawback of outdoor storage has four tiny legs. All of your bulbs will be consumed if mice or other rodents have access to them, with the exception of those that are poisonous or repulsive to them (such as Narcissus, more commonly known as Daffodils). Use steel mesh, such as hardware cloth, to shield potted bulbs.
Please be aware that for bulbs to successfully freeze, moisture is just as crucial as temperature. Every few weeks, check the potting mix in the pots, and when the surface seems dry to the touch, properly water it.
Check the pots for evidence that the bulbs have rooted as soon as the suggested rooting period has passed. The bulbs are often ready to bloom when thick white roots can be seen peeking through the drainage holes in the bottom of the pots. Give the bulbs extra time in the cold storage if you can’t see any roots. The appearance of shoots emerging from the tops of the bulbs should not be used to determine preparedness; without roots, the bulbs won’t flower as intended.
You don’t have to immediately remove the bulbs from the cold once they have taken root. Most plants will endure additional freezing period, enabling you to plan a series of winter blooms.
Bring the pots out of cold storage once the bulbs have rooted, and place them in a bright window in a cool room (one where the temperature stays below 65F). The leaves and flower stems will remain compact in bright light; in dim light, they have a tendency to flop. The bulbs most likely generated white shoots while being stored in the cold. They immediately turn green in the sunlight.
As the bulbs begin to send up leaves and blossom stems, pay special attention to how much moisture they need. The bulbs won’t likely need watering more regularly than once per week at first, if at all, but by the time they bloom, you might need to water them every other day or two.
The majority of bulbs will blossom 2–5 weeks after emerging from the cold, bringing with them the pleasant scents and vibrant hues of spring. The length of bloom varies depending on the variety and bulb type, but it is typically less than you’d anticipate with garden-planted bulbs. The demise of the blooms is accelerated indoors by warm temperatures and low humidity. To extend bloom, move the pots out of direct sunshine and into a cool space at night.
We often advise placing the bulbs on the compost pile after the blossoms have faded. After the risk of a heavy frost has gone, forced bulbs can be planted in the garden if you keep them in a sunny window and keep watering them, but they won’t bloom properly again for at least two years. Daffodils, Crocus, and Grape Hyacinth are more likely to be worth the effort of planting than Tulips, which rarely bloom again.
Hyacinths can be forced in glass jars, water with pebbles, or both. If forced in this manner, they still require a cool rooting period. Only the bulb’s roots reach the water in special forcing glasses that have been in use since Victorian times and are designed like an hourglass to keep the bulb’s bottom dry. If you’re putting pebbles in a different kind of container, fill the bottom of the bowl or pot with a layer or two of pebbles, such as pea stones, marble chips, or river rocks. The top third of the bulbs should be exposed when the bulbs are placed on top of the pebbles and then filled with more stones. Make sure to keep the bases of the bulbs above the water line while adding enough water to serve as a reservoir for the roots. The bulbs will perish if they are left in water. Then, after 4–8 weeks, keep the container in a dark, cool location (40–50F). Regularly check the water level and top it off as needed to keep it below the bottom of the bulb. It’s time to relocate the bulb into a bright window in a cool room once the roots have formed and the leaves have started to grow (one where the temperatures stay below 65F). After the risk of a heavy frost has gone, bulbs that have been forced in water can be planted in the garden, but they won’t bloom well for at least two years, if not ever.
Although experts frequently advise extremely long cold spells, we’ve had success at home utilizing the minimums given here. Keep in mind that bulbs can continue to cold for longer than the required time. Please be aware that tulips do need the longest amount of time to successfully flower.
Do you need to keep flower bulbs in the fridge?
Daffodils, tulips, and other spring-blooming bulbs’ foliage is starting to turn yellow and brown and appears a touch scruffy in the landscape. Therefore, this is a wonderful moment to find them.
Here are some suggestions for removing the bulbs and ensuring the best blooms the following year:
Consider allowing bulbs that are growing in the lawn or close to trees or shrubs to become dormant naturally. The cost of retrieving these bulbs is not worth upsetting the roots of other plants.
Use a garden fork while digging up the bulbs to prevent harm. While it won’t chop any bulbs in half or sever any roots, using a shovel could result in those things happening.
Knock off any loose soil after a bulb is above ground, but do not wash them. Bulb rot can be brought on by water. Remove the bulbs’ leaves and roots.
Find a temporary storage location for the bulbs that is cool, dry, and dark; do not use the refrigerator just yet. Before putting spring bulbs in the refrigerator, they should be left out for 48 to 72 hours to air out a bit. The best place to store them is on a wire rack or shelf, but any shelf in your garage or home’s closet will work as a temporary location. The bulbs should not contact when you spread them out. All of the bulbs should have air flowing between them.
Set the bulbs aside to dry for a few days before packing. For storing, brown paper bags are excellent. For good bloom development the following year, the bulbs must be stored in the refrigerator for at least six to eight weeks.
When should bulbs be placed in the refrigerator?
According to the Clemson University website, tulip bulbs must be forced out of dormancy by being refrigerated for 12 weeks at or below 40 degrees Fahrenheit in order for them to bloom. Three months after you first place them in cold storage, take them out of the fridge. Put the tulip bulbs in the fridge by the end of October, and take them out in late January, for instance, if you want the flowers to blossom in February.
Although the bulbs must be kept cold, cold storage by itself won’t cause the tulips to bloom. After the cold treatment, pot them properly and give the right cultural conditions for them.
How are tulip bulbs pre-chilled?
In regions where the soil temperature doesn’t sufficiently cool during the winter, often USDA Zones 8, 9, and 10, spring-blooming bulbs need to be pre-cooled, or pre-chilled. Here, pre-cooling is necessary for crocuses, tulips, and hyacinths. Place bulbs in the refrigerator’s fruit and vegetable drawer for 8 to 14 weeks to pre-cool them. However, avoid storing them near ripening fruit as this can release ethylene gas, which can harm the bulbs. The bulbs should then be planted right away in the garden or in pots.
In areas with mild winters, consider bulbs that don’t require pre-cooling to avoid having to do it. These include, among others, daffodils, narcissus, iris, freesia, scilla, and triteleia. A reputable bulb catalog will specify which options need for pre-cooling and which are suitable for warm winters. Numerous bulb suppliers also provide pre-cooled bulbs; they will preserve your purchase in a cold storage facility and send it to you when planting time arrives (December or January in warm areas).
Check out our two illustrative how-to files, Gardening with Bulbs & Tubers and Bulbs.