Most of our favorite flowers that grow from bulbs bloom in the spring. But when is the best time to plant them?

Bulb flowers such as allium, crocus, cyclamen, daffodil, fritillariairis, Siberian squill, and tulip should be planted in the fall, so they can undergo the winter chilling they need to bloom in the springtime.

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In this article, we discuss guidelines for choosing the best time to plant bulbs, and what to do if you miss this optimal window of opportunity.

First, let’s talk about the word “bulb,” in both the strict and broad terms of its definition.

What Is a Bulb?

A bulb is a type of geophyte, or a plant that’s propagated via an underground storage vessel that contains all it needs to grow and flower.

Inside are a growing bud and leaves. On the outside are roots and a scaly brown wrapper called a tunic.

Because of the tunic, true bulbs are often described as “tunicate.”

The word “bulb” is commonly understood as an umbrella term that not only applies to true types, such as the garlic, daffodil, hyacinthand tulipbut also to other fleshy-rooted plants, including ones that grow from corms, rhizomes, tubers, and tuberous roots.

These others vary in appearance and growth habit, but are also types of underground storage units.

So, although the crocus is a corm, and the caladium is a corm/tuber (depending upon who you talk to), and the iris is a rhizome, if it blooms in the spring and grows from one of these various underground storage units, that’s what we’re talking about.

We refer to these vessels of spring as “hardy” because they winter over outdoors, and experience the chill needed to enable them to break dormancy and burst into the spring flowers we know and love.

When to Plant

It’s easy to figure out which bulbs should go into the ground in the fall, because most vendors make them available just in time for planting.

And while you may be inclined to pop them right into the ground, there are a few crucial guidelines that can help you achieve the best results.

Per “Rodale’s Ultimate Encyclopedia of Organic Gardening,” planting requires ground temperatures that are below 60°F at a depth of six inches.

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Rodale’s Ultimate Encyclopedia of Organic Gardening

However, regularly taking the temperature of the soil to discover when the time is right can be a nuisance.

Alternatively, you may use nighttime temperatures as a guide. When they stay in the 50s or below for two weeks, the time is right.

And finally, these amazing self-contained storage units require four to six weeks to grow roots before the first frost.