The Best Time to Plant Bulbs
The best time to plant your bulbs is not when the stores start selling them. Just as they rush the holidays, retailers are also guilty of rushing the planting seasons. I've seen tender annuals offered for sale well before the last frost date and bulbs on the shelves when it is way too warm (or too cold) to plant them. So when is the ideal time to plant bulbs?
Plant Twice a Year
Bulbs are planted twice a year. In the fall, you plant bulbs that will bloom in the spring such as crocuses, daffodils and tulips. The reason that they are planted in the fall is that they need to be chilled before they break dormancy and begin growing and blooming. They are left in the ground after their foliage dies and the bulbs go dormant. Most will continue to come up every spring and even multiply.
Summer blooming bulbs such as gladioli and dahlias are treated like annuals. The bulbs are planted after your last frost date and dug up in the fall after the foliage dies. These bulbs will die if left in the ground over the winter. They need to be stored in a cool, dry, dark place over the winter and then replanted in the spring.
If you purchase your bulbs from a catalog, they will be sent to you at the proper time for planting. For spring blooming bulbs, I usually wait even later. If you purchase your spring blooming bulbs from a store or nursery, you definitely should wait until the weather and the soil have cooled. Why do you need to wait until the soil has cooled? Bulbs need to establish roots after they have been planted but if the soil is too warm they think that it is spring and start to send up their leaves. Even though the foliage will go dormant during the winter, you don’t want your bulbs using up their energy producing foliage in the fall.
The Rules For Planting Fall Bulbs
Here are some rules of thumb for planting fall bulbs:
Zones 1-3 should plant from late August through September
Zones 4 and 5 should plant late September through early October
Zone 6 should plant by mid-October
Zone 7 should plant by early November
Ignore the Rules!
Now ignore those rules. I live in New Jersey, zone 6, and mid-October is way too early to be planting bulbs. The soil is still too warm, especially with the advent of global warming. I’m sure at this point you are asking yourself how to measure soil temperature. No, you don’t stick a thermometer in the ground. Dig a hole several inches deep and stick your hand in it. If the soil feels warm, it’s too early to plant. If the soil feels cool to the touch, it’s time to get planting! A good rule of thumb is to wait until you have had at least two weeks of 50°F (10°C) night time temperatures before checking the warmth of your soil.
No Winter? No Problem!
Those of you who live in parts of the country where winter is either very warm or non-existent can also have wonderful spring flowers. Store your bulbs in your refrigerator for 3 to 4 months to provide the necessary chill that they need, then plant them directly in your garden.
For bulbs that are planted in the spring for summer blooms, you need to be concerned with frost dates. A heavy frost will kill any foliage that your bulbs have produced. Here are the average last frost dates for US growing zones:
Zone 1 June 15
Zones 2 - 4 May 15
Zones 5 - 7 April 15
Zone 8 March 15
Zone 9 February 15
Zone 10 January 31
Last Frost Dates Are Only Averages
Remember, these are averages. Here in zone 6, we have had killing frosts after May 1. If you have tender plants in your garden and you are expecting a late frost, throw a sheet over them for the night to protect them.
I always wait until four weeks after my last frost date to plant my annuals. They are heat loving but don’t like the cool nights we sometimes have in May here in New Jersey. My summer bulbs, however, I plant two weeks after my last frost date. I know that it will take up to two weeks for the foliage to start growing and by then, the danger of frost will be past and the heat upon us.
Knowing When to Plant is Easy
Knowing when to plant your bulbs is easy if you know what your bulbs need. Don’t be impatient. In the fall, wait for your soil to cool down before planting. In the spring, wait until after your last frost date before planting your tender summer bulbs. Follow these two simple rules and you will be rewarded with years of blooms.