So many of spring’s favorite flowers come from bulbs planted in fall. From daffodils to tulips and snowdrops to hyacinths, these darlings of the spring season all perform best when planted before the winter cold sets in.
For many bulbous perennials, planting at the right time of year is one of the most important factors in garden success. Many of these plants require a period of cold weather to tell them when they should be dormant and when it is time to wake up and begin their growth cycle.
The deadline for fall planting does not apply universally to all gardeners. The climate in which you are located plays the most significant role in timing your bulb planting.
It is important to pay attention to the weather forecast, especially if you live in a climate that commonly experiences a hard freeze early in the season. The timing is more flexible in warmer climates, where you may never experience a hard freeze.
When Should I Plant My Bulbs?
Planting late can impede root development and leave plants vulnerable to freezing temperatures.
A good rule to abide by when deciding when to plant your bulbs in the fall is to plant them about six weeks before the ground freezes. This gives them time to establish some roots, which will help them to survive the cold months ahead.
If you plant too late, they may not get established and can be more vulnerable to freezing temperatures. You want them to enter into dormancy gradually, as they would in a natural environment. You also don’t want to plant them too soon while the soil is still warm.
The ideal soil temperature for planting in fall is between 40°-50°F. If the soil is too warm when you plant your bulbs, they may think it is time to start growing. Once this happens, they become more susceptible to rot, which can mean a total loss.
Soil Temperature
Your soil temperature should be just right if you wait until the air temperature is consistently in the 40s and 50s for about two weeks. If you’re unsure, you can dig down a few inches and feel the soil beneath the surface. If it feels warm to the touch, it’s best to wait a bit longer.
In colder climates, such as those north of Zone 4, you are likely to need those bulbs in the ground in early September. If your climate often experiences freezing weather in early to mid-October, waiting much longer than early September means you’ve probably missed your window.
If you live in a warmer climate, like zone 8, for instance, it’s best to wait longer. It is rare for the ground to freeze, although it can happen. I am in zone 8, and we had a very cold Christmas week last year that caused damage to many plants that would ordinarily survive winter just fine.
In warmer climates, consider waiting until October so that you don’t run into growth and, consequently, rotting issues. Remember that a few days of cooler temperatures won’t affect the soil temperature.
In zones 7 through 5, plant in late September to early October. You should be in good shape if you follow the above temperature guidelines. The ground typically freezes about six to eight weeks after the soil temperature hits that 50° mark.
What To Do If You’ve Missed Your Window
These bulbs require exposure to cold weather to initiate their growth and flowering process.
So, what should you do if you’ve missed the window for your climate zone and are left holding onto those bulbs until spring? Remember that we plant in the fall because they require a period of cold weather to initiate the growth and flowering process.
Without this period of cold weather, many will not grow, and the ones that do may be much less robust than they otherwise would be. This is where cold stratification comes in. There is a way to give your bulbs what they need in terms of temperature artificially.
Cold stratification is the process of mimicking nature’s temperature cycles. By following a few simple steps, you can ensure that your bulbs get what they need and will know when it’s safe to start growing and blooming.
How to Do It
Less chill time is needed for types that sprout early.
Different bulbs require different amounts of what we call chill time. Chill time is the amount of time they need at cooler temperatures to initiate their growth cycle. The earlier they sprout, the less chill time they require. Those that sprout later on will likely need more chill time to complete their dormancy cycle.
This process can also be done at different times of the year, allowing you to force bulbs and grow them indoors. It is possible to trick your bulbs into thinking it is time for them to sprout. If you’ve ever wondered how it’s possible to buy tulips for Mother’s Day and even later, this is how that works!
Cold Stratification
To cold-stratify your bulbs, you need to know how to do it and how long your specific types need to chill. Let’s run through the cold stratification process before discussing specific chill times.
Most spring bloomers need a chill temperature no higher than 40°F. Storing them at a cooler temperature is fine for many, as they are frost tolerant, but any warmer and they may not stay dormant. This is right around the temperature at which most folks keep their refrigerator, which is a great place to store your bulbs.
Keep them away from fruit in the fridge, as fruits release ethylene gas, which reduces the blooming of your bulb plants. You can store your bulbs in a mesh or nylon bag, as these items are breathable.
Storing in paper bags will also work since the paper absorbs moisture. However, don’t store them sealed in plastic; this will retain moisture and cause your bulbs to rot. For the same reason, you want to store your bulbs dry.
Cleaning and Storage
To prep your bulbs for winter, make sure they are clean. If you’ve recently dug them up, you must wash them. Rinsing off any residual soil will help prevent fungus and bacteria from invading while in storage.
Once clean, allow them to dry or cure. This involves leaving the bulbs exposed to air at room temperature for about two to three days. We don’t want our bulbs to dry out inside. We just want the outside to be fully dry.
After your bulbs are clean and dry, wrap them in paper, place them in other breathable containers, and tuck them away in the refrigerator. Inspect them occasionally; once every two to three weeks should suffice. This is to look for any signs of trouble, such as rot or drying out.
Which Bulbs Need to Chill?
Determining the necessary fridge time for bulbous plants is quite straightforward.
In general, if you know where your bulbous plants are native, it’s not difficult to deduce how much time they will need to spend in the fridge. Plants native to warmer climates, such as zones 9 through 12, will not need this chilling time, and in fact, they may need to be brought indoors and stored away from the cold, which can kill them.
For bulbs that grow in colder climates, look to the time each plant typically emerges in spring or late winter in some cases. The earliest bloomers need the least chill days, while those that bloom later in spring will likely need up to several months of chill time.
Refer to this chart to determine how long to keep your bulbs chilling. It’s good to indicate when you started chilling and when you intend to take them out.
| Name | Chill Time |
| Allium | No Chill Time Required |
| Bearded Iris | No Chill Time Required |
| Camas Lily | 60-100 Days |
| Common Bluebell | six weeks |
| Crocus | 12-16 weeks |
| Crown Imperial | minimum of three weeks |
| Daffodil | 10-14 weeks |
| English Bluebell | minimum of six weeks |
| Foxtail Lily | minimum of three weeks |
| Glory-of-the-Snow | 10-14 weeks |
| Grape Hyacinth | minimum of three months |
| Hyacinth | 13-15 weeks |
| Lenten Rose | minimum of three weeks |
| Peony | Three months |
| Siberian Iris | 60 days |
| Siberian Squill | 10-14 weeks |
| Snake’s Head Fritillary | four to six weeks |
| Snowdrop | three to four months |
| Starflower | two to four weeks |
| Tulip | 12-14 weeks |
| Winter Aconite | seven to eight weeks |
Final Thoughts
If you’re concerned that you may have missed your window for planting bulbs this fall, don’t despair. There is still time to prepare for the winter using cold stratification and the appropriate number of chill days. Your bulbs will be ready to go in the ground as soon as they thaw in spring, and I promise they won’t be mad that you forced them.
