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.
When should refrigerated bulbs be planted?
The majority of spring-blooming bulbs, such as tulips, daffodils, and crocuses, are native to regions with harsh winters. In order for these bulbs to blossom successfully, you will need to “pre-chill” them if you live somewhere with moderate winters and little frosts (zones 8–11). The steps are listed below.
Warmer climate-adapted bulbs don’t need to be chilled first. These include Scilla peruviana, Freesia, Ranunculus, Anemone DeCaen, and Anemone St. Brigid. These winter-hardy bulbs can easily be planted in the fall for spring blossoms where they are located (zones 8–10).
The majority of bulbs that bloom in spring benefit from 10 to 14 weeks of freezing at 35 to 45F. These freezing temperatures cause a biochemical reaction in bulbs that “activates bloom production and starts root growth.” The bulbs will attempt to bloom without a cooling phase, but the flowers may be tiny and distorted. Bulbs can be pre-chilled for a longer period of time than advised, but not for any shorter period.
Start chilling the bulbs in mid- to late-October for best results, then plant them outside as soon as the chilling phase is over. As a result, the bulbs have more time to grow roots before concentrating on flowering. The bulbs will be prepared for planting in January or February if the chilling cycle is started in late fall.
As long as you don’t keep any fruit in the refrigerator while the bulbs are chilling, chilling your bulbs there is a simple choice. Ethylene gas released by ripening fruit will harm the developing blooms inside the bulbs. If you do decide to keep the bulbs in the fridge, make sure to put them in ventilated plastic bags to prevent drying out while they’re cooling.
Remove the bulbs from the refrigerator and plant them right away after they have chilled for the necessary period of time (see below). Select a planting place that will be shielded from the afternoon sun to prolong the bloom period. To assist retain moisture and keep the soil cool, you can cover the soil with a few inches of mulch after planting the bulbs.
The majority of pre-chilled bulbs will blossom 4 to 6 weeks after planting. Always treat pre-chilled bulbs like annuals.
Spring-blooming bulbs that should be pre-chilled at 35-45F
- 15 weeks Glory-of-the-Snow (Chionodoxa)
- 15 weeks for crocuses
- 12–15 weeks for hyacinths
- Muscari grape hyacinth: 12–15 weeks
- 16 weeks for daffodils
- 12–15 weeks for the Siberian squill (Scilla siberica).
- 10 to 14 weeks for tulips
- Galanthus (snowdrops): 12–15 weeks
- 13–15 weeks for iris reticulata
Which bulbs require cooling?
Tulip planting in the spring is one of our favorite gardening rituals because it produces a stunning display of readily cut flowers for Easter, Mother’s Day, and other special occasions that call for elegant arrangements. The only spring flower that has to be chilled before growing is tulips, but there are others as well. The following is a list of every variety available at Plants for All Seasons that must chill before planting:
- Tulips
- Crocuses
- Hyacinths
- Daffodils
- Muscari
- Snowdrops
- Alliums
- Irises
- Russian Squirrel
Are tulip bulbs required to be chilled?
Tulipa spp. bulbs need to be refrigerated. They can be kept in a refrigerator, where the cold temperatures are needed to force the bulbs to bloom indoors during the off-season. Depending on the cultivar, tulips can survive in U.S. Department of Agriculture plant hardiness zones 3 through 9, but they may also need cold treatment in regions with mild winters. The tulips will bloom beautifully and at the correct period if the bulbs are taken out of the refrigerator at the proper time.
How long should tulip bulbs be cold for?
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 are pre-chilled bulbs forced?
- Tip The best way to chill bulbs is to keep them in a fridge. In a refrigerator, temperature regulation is most effective.
- Tip When using a refrigerator to chill bulbs, keep produce out of the fridge. The bulbs of several fruits and vegetables perish because of the ethylene gases they release.
- Tip The process of chilling depends on the development of the roots. Give roots adequate time to mature before leaf and blossom development.
- Tip Prior to chilling your bulbs, plant them in containers. At the start of the chilling process, put the potted bulbs in the fridge.
- Tip You can keep the bulbs outside if you don’t have a refrigerator and live in a cool region. It is recommended to bury the pots while keeping potted bulbs outside to cold. Burying the pots aids in insulating the bulbs, shielding them from any damage from freeze-thaw cycles. Protect the buried pots by encasing or covering them with chicken wire or hardware cloth if voles and squirrels are a concern in your neighborhood.
- Tip To keep the soil moist while it is chilling, use a spray bottle.
- Tip The tops or “necks” of the bulbs should be visible and approximately level with the soil surface when planting bulbs in pots for indoor forcing.
- Trick Use this tip to grow tulips in vases or other containers filled with water and pebbles: Tulips should be forced into soil-filled containers to develop roots. Remove the bulbs from the soil once the leaves, stems, and buds have appeared. Remove the soil from the bulbs, then put them in a glass container with water, pebbles, or stones.
- Tip Paperwhites and hyacinth bulbs can be grown in a vase with nothing more than water or pebbles.
- Trick For a longer bloom time, layer different varieties of bulbs in the soil in the container. Place larger bulbs closer to the pot’s bottom and smaller bulbs closer to the pot’s top. For the formation of roots, leave at least 6 inches of soil over the bottom layer of bulbs.
- Trick When the bulbs have sprouted, fill the container with moss or succulents. When the bulbs have finished blooming, the pots will still be filled with greenery for you to enjoy.
- Tip At a pot with drainage holes in the bottom, plant your bulbs for indoor forcing.
- Tip After the initial 12–16 weeks of chilling, gradually acclimate the bulbs to warmer temperatures. For the first three to four weeks, move the pots to a setting between 50 and 60 degrees with indirect light.
- Trick Plant forced bulb pots outside with pansies and other cool-weather annuals in the spring after keeping them in pots all winter.
- Tip Throughout the developing phase, check your bulbs every week to make sure the soil is neither too damp or too dry.
Before planting, should bulbs be soaked?
You now understand the fundamentals, but you could still have some queries. Here are some of the questions regarding planting bulbs for spring that I am asked the most.
How deep should you plant spring bulbs?
It’s a good idea to put spring bulbs 2-3 times deeper than their height as a general rule of thumb. For the best results, however, always read the package directions.
Should you soak spring bulbs before planting?
Before planting, there is no need to soak them. However, soaking them for 12 to 24 hours can hasten the roots process if you are running late planting them.
They will root more quickly if you add fish emulsion or liquid kelp to the water before soaking.
Why are bulbs planted in the fall?
To grow and blossom, spring-blooming bulbs require a period of cold hibernation. They won’t likely blossom in the spring if they aren’t planted in the fall.
Can you plant flower bulbs in the spring?
Although it is technically possible, I don’t advise planting cold-hardy flower bulbs in the spring. If they are planted in the spring, they won’t bloom.
Additionally, there’s a chance they won’t have enough time to save the energy they’ll need to endure the winter.
Bulb planting offers such a big payoff for spring blooming. Seeing the first few green shoots pop up from the earth is so amazing. And I bet you’ll be putting more and more spring bulbs in your garden every year now that you know how simple it is.
Tulip bulbs—can I freeze them?
Putting bulbs in the freezer will kill them since it is too cold. This is the ideal temperature for a refrigerator, which is often around 4C. Before the end of March, place the bulbs in a breathable container, like a paper bag, and begin chilling. Continue for a minimum of eight weeks before May planting.
What occurs if tulip bulbs are not chilled?
In her Virginia garden, my grandma used to raise tulips. I really like them and would like to plant them in my garden, but I’ve heard Southern California doesn’t get cold enough. Ist das so?
Answer: There are two parts to the response to your query. It is true that the temperatures around here don’t drop low enough for tulips to establish a root system and return year after year like they did in your grandmother’s garden.
The key is to consider them as a “annual bulb” and pre-chill them in your refrigerator before planting. Tulip bulbs can be chilled in the refrigerator to simulate the chilly evenings of tulip-growing regions like Holland.
Tulip bulbs must be cooled. The ensuing flowers won’t be as tall and full without freezing.
Tulips rarely come back for longer than a year or two due to our warm winters. Despite the fact that some gardeners attempt to dig the bulbs up and refrigerate them, experts claim that this normally isn’t very successful.
Tulip bulbs, which ought to be showing up in nurseries, are a wonderful time to start purchasing them right now. Purchasing now ensures that you get the finest selection even though they will be available throughout the following two or three months.
Depending on the kind, tulips can bloom from March to May each spring. For the longest season of color, try planting early, mid-season, and late kinds of tulips because their bloom is famously short-lived. Tulips of the same variety planted at different periods won’t often produce a longer show because each type is bred to bloom at a given time, regardless of when it is planted.
* To keep tulip bulbs chilled for at least six weeks, put them in a paper or plastic bag that has been hole-punched. Avoid placing bulbs close to apples because they release ethylene gas, which rots bulbs.
* From late November to the beginning of January, the bulbs can be planted. Just be careful to keep them chilled until you’re ready to plant them since after they’ve been out of the cold, they tend to weaken and mold.
* Offer superb drainage. Tulips won’t survive in muddy soil. Before planting, it’s crucial to generously amend your soil with perlite or pumice and handmade or bagged compost. Gypsum is also advised if your soil is heavy clay.
* Use high-quality potting soil with plenty of perlite or pumice, or mix some into the soil to make it lighter. Tulips thrive in containers, where they frequently create gorgeous displays, and do particularly well.
Tulip bulbs should be planted in the earth 5 to 6 inches deep and 5 inches apart, pointy end facing up.
Tulips can be grown in large numbers in pots. They can be positioned in pots such that they are an inch apart and touching. Place bulbs against the pot’s edge and work your way inside in a circle until you reach the middle.
Does cold stratification apply to tulips?
Tulips (Tulipa spp. ), which you can naturalize in garden beds or grassy areas, adorn gardens in the late winter to early spring with their many hues and hundreds of various types. According to the Texas A&M University Aggie Horticulture website, these traditional bulbs are used to dry summers and contrastingly chilly winters. Tulip bulbs require cold treatment but not moist stratification or storage in a moist soil mix in order to grow successfully.