Plant Annuals Or Perennials? Why Not Both?

I’ve heard the question at least a dozen times. Why should I plant annuals in my garden when perennials flower year after year after year and the annuals are shot in one season?

And there are probably a dozen answers. I think the simplest, though, is that there are times when annuals work and times when they just don’t work. You won’t find too many of them blooming in the garden in April or early May. By the same token, there is a gap time in most gardens when the perennials (which can start blooming in March) fade for several weeks in late summer and leave holes in the garden. Annuals and tender plants can fill these holes really well.

Only a well accomplished and talented gardener can do a garden with just annuals or just perennials. But it also takes talent and experience to know how to use annuals as fillers to brighten up those doughnut gaps in the garden that happen between the time when the summer perennials fade and the fall perennials begin to shine. For some this dilemma is a challenge while for others it’s an opportunity.

To keep it simple, let’s agree that annuals flower once and perennials flower more than once. Would that it were that simple. The fact is that annuals go through their entire life cycle in one growing season. The seeds germinate, the foliage and roots grow, the plant flower sets seed (or tries), and at the first cold snap or frost it dies. If the plant is what we call a hardy annual (nearly, but not quite an oxymoron), the plant flowers, sets seed and the seeds fall to the ground, but the seeds are winter hardy and under the right conditions will likely germinate the next spring.

Perennials are quite different and for the most part we don’t rely on their seed for propagation, but on their roots and crowns. This is not to say that perennials can’t be grown from seed, but most of our modern perennials are essentially clones of their parents, as this is how we can be sure that every iris, peony or phlox of the same name is a mirror image of its sibling. This is very difficult to accomplish with plants grown from seed ... except F1 hybrids, which are usually annuals.

We loosely define perennials as plants that grow from below-ground portions that are usually roots. The shoots emerge from the roots each spring, elongate, and produce foliage and usually flowers. During the growing season the plant rejuvenates the root system, where enough energy is stored for overwintering. The shoot system dies to the ground at the end of the growing season, goes dormant and then emerges again the next spring.

This points up one of the greatest assets of the perennials. You buy them once and for most of them they return year after year for years and years. Even better, most can be divided and multiplied right in the garden. This is important to remember when you’re spending $15 or more for a potted perennial, as it will give you years and years of service as well as dividends.

The dividends (or return on investment) come when you divide your perennials and make more ... for free. So while you spend 15 or 20 bucks for that nice iris or peony, in a few years you can divide it and in no time that one perennial may have cost you as little as or less than a similar six pack of annuals ... that died years ago. But again, will that perennial be flowering on a 90-degree day in August when a marigold, celosia or bedding dahlia, all annuals, are thriving and in full bloom?

Now let me add a bit of confusion to the mix. There are plants that we call tender perennials and of course there are biennials. Many gardeners actually grow a tender perennial and don’t even know it. This plant has fairly inconspicuous flowers but we actually grow it for its fruits. It goes by the name of tomato and in South America, where it’s native, it’s a true herbaceous perennial. In recent years, though, many other tender perennials that have tropical origins have been introduced into the summer garden, and they can be lifted and brought indoors for the winter or treated as annuals.

Biennials are plants that establish their roots and shoot system (foliage) during the first growing season but don’t flower. In the second growing season they flower, then die before the next winter. While hollyhocks are often sold as perennials, they are actually biennials, though from time to time a plant will manage a third year. What fools many gardeners is that hollyhocks will self-seed, and in the right conditions the seedlings will result in new plants, giving the appearance that the plant flowers every year. Delphiniums, especially the taller varieties, are also considered to be biennials or short-lived perennials—another variation on the theme.

Now it’s time for me to admit to my bias. If you haven’t already noticed I’m a perennial lover. My garden is composed entirely of perennials. It’s been an addiction for at least 40 years, but now that I think about it my father never planted annuals either so it may be an inherited (or learned) trait. If you want a long-term gardening challenge, build a perennial garden that’s blooming and attractive from March through October. But annuals really do have a strong place in a proper garden.

There are times when spaces in a garden simply can’t be filled by perennials, and unless you are a really experienced gardener there are gaps in the garden that can be effectively filled with annuals. These gaps usually occur during the late-summer period when the summer perennials have finished blooming and the late perennials haven’t started yet. The reason why annuals fit into these gaps so well is that they have their genetic origins in hot and dry or tropical locations like Mexico, Central and South America. They not only fill the doughnut holes, but they thrive.

Annuals also serve a strong function in planters and pots where perennials simply aren’t practical, and many varieties are well suited to mass plantings where drifts of color are part of the plan and can be accomplished with the flowers, the foliage or both. And don’t forget that annuals can be grown from seeds that are started indoors, in situ, or from cell packs. Annuals like marigolds that are seeded directly in the garden in early summer are perfect for mid-August and September blooms.

Here’s a challenge for you. Now that the annuals and perennials are showing up on local garden center benches, take a look at the prices. See how much a flat of annuals will cost and consider how long they will last and how much space they will take up. Then find a perennial plant that might serve the same function and look at the cost of one plant, remembering that over a few years you can divide it and it may cover that same space as the flat of annuals that would need to be replanted every year. Consider it a challenge, but also remember that annuals still have their place and can’t always be replaced with perennials. I never said it was easy, but keep growing.