Planning for Annuals Vs. Perennials: What’s the Difference?

As the Sierra Gardens coordinator, a lot of people have asked me about the difference between annuals and perennials, so I thought I’d give this question some attention while there still plenty of time to dream and plan for your spring and summer garden.

 An annual plant is a plant that will complete its entire life cycle within one growing season.  In other words, it will flower and fruit in one season, and then die off. Most of the veggies that we grow in our gardens are annuals. They produce flowers and then fruit, and then at the end of the season you yank the spent plants out and feed them to the compost pile. Lots of bedding plants and common garden flowers like marigolds and zinnias and sunflowers are also annuals, and many herbs such as Basil and Dill.

You might say “But Edy, I had sunflowers in my garden once and they still come back year after year!” That’s because many annual plants re-seed themselves quite readily. In the case of sunflowers, it is often with the help of birds who help move the annual seeds around the garden. Nurseries will often refer to plants with this tendency as re-seeding annuals. I have a zinnia patch in my back yard that comes back year after year….of course it’s never where I want it, but I let it grow anyway, because I can’t resist an entire patch of zinnias. Some re-seeding annuals like amaranth can become quite weedy over time (they have millions of tiny seeds!). Others can be controlled by deadheading, which is the practice of cutting off spent flowers before they produce and drop mature seed.

A perennial plant has a much longer life cycle, it will come back season after season, and may not actually make it to fruit or flower within its first year.  Some perennials remain green year round and others die back in the winter time while the roots are still alive under the soil, like hostas and peonies. Obvious perennials include trees, shrubs and bushes, but there are also lots of herbaceous perennial herbs and flowers. Herbs like sage, rosemary, oregano, thyme are all perennials. Most plants used in landscaping are perennials.

Perennials may also re-seed themselves, or they may spread via their root system. Herbaceous perennials tend to expand in size every year until they reach their typical mature size (information that nurseries generally provide when you purchase a plant).

Just to confuse matters, there are also plants that are classified as biennials. These are plants that usually take two growing seasons to reach maturity, at which point they generally die out (often re-seeding themselves). I like to think of biennials as short lived perennials. Hollyhocks are a classic example of a biennial.

To confuse matters even more, sometimes perennialism is dependent on climate. For instance, an herbaceous perennial from a warmer climate may only survive as an annual in a cooler climate. I have been able to preserve some of my favorite perennials in the greenhouse over the winter that would likely die if left outside. Currently my greenhouse is full of some of my more tender geraniums and succulents that would likely die altogether if left outside all winter.

Why does this matter? Like I said before, most common garden veggies are annuals. I often advise folks with small Sierra Gardens to keep perennial plants (like raspberries and many herbs) outside of their garden, since they have the tendency to grow larger and expand over time. For many of you, space is at a premium. Many of the perennial herbs have the advantage of being deer resistant, which means they can survive outside of the fence.

If you are planning a garden, it is good to know the basic information about the plants you are thinking of including. Is it annual or perennial? What are its sun/water needs? What is its average size at maturity? Does it re-seed easily? Will it spread from the roots… (think Bermuda grass!)? Nurseries generally provide all of this information when you buy a plant, and of course there are any number of gardening guides where you can find that information, not to mention Google! Annuals are generally planted at the beginning of their growing season when they can put their full energy into vegetative growth, whereas perennials are generally best planted when they are dormant (around here that usually means winter), so that they can put their initial energy into root growth.

I hope this clears up some questions for folks! If you are in the Sierra Gardens program and you are interested in establishing some perennial herbs around your garden let me know, and I will be happy to advise!

-Edy Cassell, Sierra Gardens Coordinator