Annuals Vs. Perennials – The Differences!

With warmer temperatures in the local forecast this weekend, it is likely that gardening is on a lot of our minds…it definitely is on mine! As you prepare to either order some plants online or perhaps visit your local garden centre I wanted to outline one of the first garden centre basics that will help point you in the right direction – annual vs perennial plants.

Whether you are shopping online or at a garden centre, plants will typically be broken separated into these two very broad categories – annuals and perennials – and knowing which one suits your needs is the first step in choosing the right plant for your home.

Here is the number one difference between annuals and perennials:

Annuals only last for one season

Perennials come back year after year

That’s it! But, knowing which one you want is the next challenge. Here are a few other differences when it comes to annuals vs perennials

First, a Note on Perennials

Perennial means a plant that is planted once and will continue to come back year after year in your garden. Perennials is also the term used to describe a flower that you plant in your garden that comes back year after year – things like black eyed susans, echinacea, russian sage…those are all perennials and they are, indeed, perennial. However, trees and shrubs also fall into this umbrella of ‘Perennial Plants’ because they come back year after year too. In this post I will mainly be referring to perennial perennials…the flowery kind…not shrubs and trees (although much of the information is true for them too). Got it?!

When do Annuals vs. Perennials Flower?

Annuals are best purchased at the beginning of each season and will flower continuously for the whole season. Once they are finished flowering, you can remove them from your garden and dispose of them as they will not come back the following year. An annual completes its entire lifecycle in one year.

There are spring, summer, and fall annuals. Spring annuals can be planted outside starting in about March and will die out in the heat around May. Summer annuals can be planted after your last frost date (May 24 here in Southern Ontario) and will last until about October. Fall perennials can be planted starting around September and will last until frost. During their planted season, annuals will look full, lush and flowery the entire time.

Perennials are planted once and will come back each year. Most perennials have a period in the year during which they bloom. Unlike an annual, in most cases it will not be for an entire season. Some perennials, astilbe or peony as examples, just blooms for 2 weeks of the year. Other perennials, like Russian Sage, will flower for a longer period of time from the end of July until frost. One of my favourite fall perennials is Japanese anemone which flowers in abundance for just a few weeks in September and October.

When perennials are not flowering they will be primarily green throughout the spring/summer/fall seasons. They will dry out and go dormant each winter in our climate. Some perennials, like echinacea and sedum will simply dry out in the winter and still have their seed heads remain. Others, like heuchera and hosta will die back completely to the dirt in the winter but reemerge naturally in the spring.

As perennials only flower for specific periods each season you will want to select perennials that are going to flower throughout the year at different times so you have extended interest in your garden. A big part of landscape design is ensuring that the garden has as much interest as possible throughout the year.

Where do you want to plant annuals vs perennials?

Annuals are best suited in a decorative seasonal planter or hanging basket. These are areas where they will give a very dramatic show for a few months and you can change the planters with the season. However, you will often see people edge beds in annuals or even plant them around the base of a tree. This is not my preferred use for annuals but, for many gardeners, adding annuals into the beds in the spring is an anticipated tradition and I definitely respect that! If you are looking to create an annual planter for your house, this seasonal planter tutorial outlines just how to do that.

Perennials are best suited out in your garden, planted in the ground, in a location where you want them to be forever.

Can a perennial go in a planter?

Yes, a perennial can be planted in a planter, however, if you want it to come back year after year there are a few things you will need to do. Perennials, when planted in the ground, receive insulation around their roots from the soil that helps them withstand freezing and thawing throughout winters- this is what kills not hardy plants. In a planter, the plants do not receive insulation and are susceptible to winter damage with multiple freeze-thaw cycles. If you want to keep a perennial in a planter indefinitely then you will need to insulate the walls of your planter using a thick styrofoam (this should be put inside your planter so it is not visible and can stay there forever). If you place a perennial in a planter without insulating it over the winter it is a perennial being treated as an annual and will likely not survive.

When should you plant annuals vs perennials?

Annuals are best planted at the start of the season for which they are grown so that you can enjoy them to their fullest during the time that they are going to grow and show. Saying this, annuals can be planted as long as there is no risk of frost.

Perennials can also be planted anytime that there is no risk of frost. I prefer to plant perennials in the spring because they have the whole season to get established before the winter comes along and therefore they will have a better chance of surviving the winter. The first winter for a newly planted perennial is always when they are most vulnerable to winter damage so ensuring they are well established is a good practice. While I prefer to plant in the spring, perennials can be planted at any point throughout the growing season until frost in the fall. If planted in the heat of summer, extreme watering will be necessary to ensure they adapt to their new environment and tolerate the heat.

Is there a size difference between Annuals and Perennials?

In general perennials are larger than annuals at time of purchase and typically reach larger sizes too. Each variety of plant, annual and perennial, reaches a different final size and that will be indicated on their plant tag.

Annuals are typically sold in sizes ranging from small 2″ ‘plugs’ and up to 6″ pots with fewer annuals being sold in larger 10-12″ pots (this size is usually hanging baskets or mixed planters). Annuals will grow very quickly to their mature size in a period of weeks to months, again, because their whole lifespan is happening in a much shorter time period than a perennial.

Perennials are most commonly sold in 1 gallon pots (with shrubs and trees being sold in a range of larger sizes). Compared to an annual that will reach it’s mature size within a few weeks of being planted, a perennial has slower growth and will become larger and stronger year after year until it reaches its maximum size where it will grow to each year after that. It is said that a perennial garden will reach size maturity after 3 years.

Which is more work?

Annuals are overall more work because they need to be selected and planted each year and maintained throughout the season. Many flowering annuals require frequent ‘dead heading’ and they need to be watered daily. Definitely manageable on a small scale like a planter but not something I would want for a larger area.

Prepping the ground for perennials is a much bigger job but ensuring that your beds are well prepped will protect your investment of perennials. However, once planted, some perennials are fine to be left to do their thing indefinitely with a once annual maintenance of clipping back old growth and applying fresh mulch to beds to keep down weeds. Perennials will need to be well watered for the weeks following their installation to help them establish but once established they are fine to just be watered by rainfall. Once established, perennials are a much more low maintenance choice.

Climate Variances

This is the final note so that you do not purchase a plant thinking it is a perennial but are disappointed to learn that it has actually been grown to be an annual variety or is an annual in our climate but perennial in others. An example of the latter would be bougainvillea – it grows beautifully in warmer climates but in Ontario it is an annual plant that can only be enjoyed in planters during our summer season. Another example are seasonal plants that are typically found at flower shops, grocery stores, or in the promotional areas at garden centres that are perennial varieties but are annual versions of them. Example plants are the colourful hydrangea you will see at Easter, some varieties of lavender, and hibiscus plants. While there are plenty of hardy perennial hydrangea, lavender, and hibiscus varieties that grow in our climate, often these plants are made with the intention of being indoor plants or summer patio plants. You can attempt to plant them outside but the rate of survival will be low.

As a final Recap:

How to Make a Seasonal Summer Planter

My Favourite Plants in each category

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