When it comes to bulbs, it can seem confusing when to do what in which season. In general, you plant spring-flowering bulbs in the fall, and plant summer-flowering bulbs in the spring. You divide spring bulbs in late summer, and you dig up summer bulbs in the fall. Now that fall is here, let’s look at this a little closer.
There are dozens of spring bulbs on the market ready for fall planting right now. By family name consider the alliums, fritillaries, Hyacinthus, tulips and daffodils. There are many more, so use the next few weeks to shop locally or from specialty catalogues to ensure a great bloom period.
Your favorite spring bulbs are winter hardy and for them to perform properly for us, they need to have the cold winter soil temperatures to trigger them to sprout and bloom. There are many kinds of spring bulbs, from those that bloom as the snow is retreating to those that bloom much later. Proper planning and selection can provide a several-week period of spring bloom; the same is true for other seasons.
Bulb bloom times are broken down into early spring, spring, summer, and mid to late summer to fall. In northern Illinois, these seasons run together, farther south in the state they more separated. Locations can be broken down into: partial shade (has at least 4 hours of sun), shade (having less than 2 hours of sunlight), and sun (having less than 2 hours of shade during the day).
As you plan, there are early spring bulbs that do very well in partial shade while those later spring bulbs do best in full sun. Typically, the early spring flowering bulbs are much smaller in size, as is their bloom. Bulbs are planted 2 to 3 times their diameter in the soil profile, but depth is often according to bulb size. Larger bulbs may need to be 6 to 8 inches deep, while smaller ones are planted 3 to 4 inches deep.
If your spring bulbs need dividing because of being overcrowded (i.e. daffodils), that is often done in the late summer after the foliage has naturally died down. You may even have to mark the area with a garden stake to find them later.
Summer bulbs, which are not winter hardy, will need to be dug up just before a killing frost or immediately after. Mark your calendar accordingly.
A lot of times it is easier to dig them up before the frost has killed the foliage, especially those that have lots of moisture in the foliage, it can get pretty messy! Once the summer flowering bulbs have been dug, they will need to cure and dry down before you can store them in a safe place for the winter. They will need to be stored above freezing temperatures, yet not too warm, or those summer bulbs will want to grow.
Summer bulbs do not require a cold treatment like spring bulbs; they are just “resting” until you plant them back outdoors or bring them into warmer temperatures to give them a head start for your flower garden. Just like starting vegetable seeds for transplants, do not start too early or your summer bulbs will be ready for outdoors long before the temperatures favor their growth outside. You will have all winter to plan for your summer bulbs, as you won’t plant them again until spring.
Richard Hentschel is a horticulture educator with the University of Illinois Extension