A Guide to Planting Bulbs
Planting bulbs is easy and rewarding. Spring flowering bulbs such as daffodils need only to be planted once for years of color. Summer flowering bulbs such as dahlias which need to be replanted every year allow you the freedom of trying them in different spots in your garden every summer.
Types of Bulbs
First let’s talk about the different kinds of bulbs. The term “bulb” refers to several different types of fleshy underground plant parts. True bulbs look like onions, shaped like a Hershey’s Kiss with roots coming out of the bottom. They should be planted point up, roots down. Corms and tubers look like flattened bulbs with roots coming out of the bottom. They should be planted roots down. Tuberous roots look like fat roots. They should also be planted roots down. Rhizomes look like dried out roots and are usually planted partially submerged in the soil. Iris have rhizomes. Don’t worry if you can’t tell which end is which. Even planted upside down, bulbs will grow in the correct direction.
Before you begin planting your spring flowering bulbs, think about the “look” you are trying to achieve. Because there is almost nothing else growing in your garden in the spring, tulips, daffodils and other spring flowering bulbs look best in masses or drifts. Planted singly, they look forlorn. You want large groups of plants to make your garden look fuller. This requires large numbers of bulbs. Digging individual holes for each bulb is tedious, not to mention exhausting. Instead, dig large holes for groups of bulbs and trenches for your drifts. Plant groups of bulbs in odd numbers, i.e. 3 or 5 or 7, etc.
How deep should your holes and trenches be? That depends on the size of your bulbs. The general rule of thumb is to plant bulbs 2 ½ times as deep as the size of the bulb. Generally, you should plant large bulbs 6” to 8” deep and 4” to 5” apart. Smaller bulbs such as crocuses and grape hyacinths can be closer together, 2” to 3” deep and apart.
You can save yourself time and effort by planting different types of bulbs in the same holes. Dig your hole (or trench) deep enough to accommodate your large bulbs which will be placed at the bottom of the hole. Cover them with soil until your reach a depth of 2” to 3”, plant your smaller bulbs making sure that you're not planting them directly over the larger bulbs, and then finish filling the hole.
Trees and Bulbs Don’t Mix
It’s not a good idea to plant your bulbs under your trees. They will be competing for the same water and nutrients. With the exception of the very earliest bulbs, the trees will leaf out before the foliage of your bulbs have finished storing food in the bulbs which will send them into decline. The plants and flowers will be smaller the following year. Plant your bulbs in a sunny garden where they will get a minimum of 6 to 8 hours of sun daily.
The ground froze, now what do I do?
What if you forget to plant your bulbs and the ground freezes? Fear not! You can plant your bulbs in containers using the same depth and spacing as you would when planting them directly in your garden. Do not allow the bulbs to touch the sides of the pot. They need the protection of the surrounding soil. Store the container in a window well or your garage during the winter. In the spring, move them outside to your yard and allow them to grow and bloom in the container or plant them in your garden when the ground has thawed.
Don’t Forget to Mulch!
After you have planted your bulbs, cover the soil with mulch. Why mulch when there won’t be any weeds during the winter? Mulch will moderate the temperature of the soil. Without it, the alternate freezing and thawing throughout the winter will cause the soil to heave, sometimes heaving your bulbs right out of the ground. A generous layer of mulch will prevent extreme swings in soil temperature ensuring that your bulbs will stay at the proper depth. Remove the mulch in the spring when all danger of freezing has passed.
Summer blooming bulbs don’t need to be planted in large groups like spring blooming bulbs. Rather than being the centerpiece, they are components of an overall design. They can blend in or contrast with your other flowers so smaller numbers are required for the desired effect.
Observe the same planting depths and spacing that you used when planting bulbs in the fall. Don’t plant them too close to your perennials so that your valuable plants aren’t disturbed when you dig up your bulbs in the fall. It’s usually a good idea to surround your bulbs with annuals which will be removed at the same time as your bulbs.
Iris: the exception to the rules
Iris can be planted in either the fall or the spring. The advantage to planting them in the fall is that they have an opportunity to develop a root system before winter. The following spring they are ready to grow and bloom. If they are planted in the spring, the flowering will be delayed because they need to develop some roots first.
Iris grow from rhizomes which should be planted only partially submerged in the soil. If you plant them deeper into the soil, the plants will fail to grow and the rhizomes will rot. Unlike other spring planted bulbs, iris are left in the ground over the winter.
No garden is complete without bulbs. Planted properly, they will reward you with years of color.