There’s nothing quite like those first flowers that bloom in spring: crocus, daffodils, tulips, anemone, hyacinths, snowdrops. It’s a sure sign that winter is retreating and warmer weather is just around the corner.
The bulbs of these flowers must be planted in fall in order to bloom the following spring. But new gardeners and even experienced gardeners get a little confused over the particulars of planting and caring for flower bulbs. Some of the most frequent questions I’m asked in fall are:
- When do I plant flower bulbs?
- How deep should I plant bulbs?
- Which end of the bulb is up?
These are excellent questions, and very important ones.
Flower bulbs are of two kinds: spring-flowering bulbs and summer-flowering bulbs. Spring-flowering varieties like tulips, daffodils, and crocus require a chilling period and are winter hardy. Summer-flowering bulbs like gladioli, calla lilies, and tuberous begonias are not winter hardy, and must be planted in spring.
But “bulbs” are sort of a catch-all term. It describes five kinds of fleshy, underground organs which certain plants use to store energy to fuel growth. They are:
- True Bulbs: Daffodils, tulips, and onions are the best examples of true bulbs. Energy is stored in modified leaves on the bulb, called scales.
- Corms : Crocus and gladiolas are the most well known flowers that grow from corms, which is actually a modified, swollen stem.
- Tubers: Potatoes and caladiums are the best examples. Tubers are thickened stems that grow underground and store all of the plant’s energy.
- Rhizomes: Lily of the valley and bearded iris are the best examples. Rhizomes are underground stems that grow horizontally and store the energy for the plant.
- Tuberous roots: Dahlia and anemones are the best examples. These are large, fleshy roots.
Many “bulbs” are actually corms, tubers, or rhizomes and look distinctly different. Most will show sprouts on their upper sides, which should be on top when planted.
When to plant flower bulbs
Most spring-flowering bulbs should be planted in early fall, before frost is expected in your area. This gives the bulbs time to spread their roots before the ground freezes or becomes too hard to penetrate. But don’t plant them too early, or they may bloom prematurely during a warm period, and won’t bloom in spring.
In most regions of the U.S., it’s safe to plant any time in October through early November. In the south, you can plant until mid-December; on the Gulf Coast, through the end of December; and on the California coast, through January. In the Northeast and Rocky Mountains, you have to plant bulbs a little earlier, anytime in September until the ground freezes.
See my post, Do You Know Your First and Last Frost Dates?
Summer flowering bulbs are planted when soil warms in spring, after all threat of frost has passed. This is right around the time that tomatoes are planted. You can also start these bulbs indoors in flower pots over the winter to get a head start.
How deeply should flower bulbs be planted?
Generally, spring bulbs should be planted two to three times as deep as the bulb is tall. A large bulb like tulip or daffodil will be planted at about eight inches, but a crocus bulb at three inches. Precision is not called for – get it in the ballpark and the flower will be just fine. For summer bulbs, the planting depth will vary according to the plant – look for the planting depth on the directions supplied with the plant.
Which end of the bulb is up?
When you look at a flower bulb, the bottom, called the root plate or basal plate, is where the roots attach. You might have guessed that this is the part to plant downward. Most true bulbs, like tulips and daffodils, have a pointed tip, which makes top identification easy. Tiny bulbs like poppy anemones make it very difficult to distinguish top from bottom with the naked eye. Fortunately, small bulbs like these can be planted in any direction – the shoots will orient themselves towards the sun.
Tips for planting flower bulbs
The basal plate or tip of the bulb is more obvious on some bulbs than others. If up/down is not apparent, lay the bulb on its side – the flower will grow in the correct orientation.
Good drainage is essential for flower bulbs. In soils that drain poorly, bulbs may develop rot, or won’t be properly fed. The best soil for growing bulbs is loaded with organic matter like compost and peat moss.
If you’re preparing a new garden bed, dig and loosen all of the soil to the planting depth of your bulbs. If your soil is mostly clay, work generous amounts of compost and peat moss into the planting bed. Press the bulbs into the soil and then backfill with the original soil and more compost.
If you’re working in an established bed, dig the hole with a garden trowel or bulb planter. The holes should be several inches deeper then the appropriate depth for the bulb, to allow for additional compost or peat moss. After filling the hole, press in the soil/compost with your fingers to remove any air pockets.
Bulbs of all types need phosphorous for root development. At planting time, mix a little bonemeal into the lower part of the hole, so the roots can use it right away. Phosphorous moves very little in the soil, so it’s best to place it where it will have the most benefit – in other words, not on top of the garden bed.
Water deeply after planting to settle the soil in the bed and give the roots moisture to start to go to work. But don’t over water, as too much moisture will rot the bulb. In the case of fall-planted bulbs, little extra moisture is required beyond what you give it at planting time and what Mother Nature provides. In the case of spring-planted bulbs, make sure they get one inch of water each week, either from rainfall or a watering can. They’ll also need this much water as the flower begins to develop.
Don’t fertilize bulbs after the flowers start to develop, as it encourages bulb rot and may actually shorten bloom time.
Summer, not fall, is the dormant time for spring-flowering bulbs. This is when the foliage dies back, as do the roots. When fall comes, the roots grow to provide nutrients and begin the energy storage cycle for the next flower bloom. This is why spring-flowering bulbs should be dug or divided in summer, not fall.
When you buy bulbs, buy enough to fill the space. Nothing looks lonelier than a tulip separated from its companion tulip by a few feet. For large flowers, space them 3-6 inches apart, and for small flowers like crocus, 1-2 inches. A mass of flower blooms close together looks much better than a wide spacing.
When the flower has finished blooming, only remove the flower stalk, not the foliage. The foliage goes to work after the bloom, gathering energy from sunlight to store for the next cycle. Only remove the foliage when it has died back on its own.