Can Flowers Be Composted? (Some Things To Keep In Mind)

Composting with old flowers is a great way to keep your garden healthy and your plants well-nourished, while also reducing waste and conserving resources. Every time I can add something to my compost bin, it means that I’m reducing my organic waste going to the landfill, whether it’s deadhead from the garden or the vase of flowers on the kitchen counter that are past their peak.

Flowers are excellent material for the compost bin. They provide both the nitrogen and carbon needed for healthy compost. Flowers that have been treated with any toxic herbicides or pesticides should not be composted, but most other flowers can be chopped up and added to the compost pile.

Let’s take a closer look at which flowers are perfect for composting as-is, which need a little preparation before adding to the compost bin, and which flowers are best kept well away from your compost.

Can flowers go in my compost?

Flowers make excellent material for compost because they are a blend of both green and brown waste, both of which are necessary for making good compost. The brown waste gives the compost its carbon component, while the green waste gives the compost its nitrogen component.

“Browns” can refer to any flowers you snip off while deadheading, cool-season spring flowers that are done blooming, and any other dried-out or dead material you cull from the garden. 

Any live plants, trimmings or thinnings from a too-dense sowing can also go in the compost pile as a “green” component Annuals that have gone to seed will be a mix of both green and brown waste because some of the plant material will still alive with lots of nitrogen in its stems and leaves, while some of the dead flower heads contain large amounts of carbon.

Sometimes I’ve been lazy in clearing away annuals from my landscaping and garden, and by the time I get to them, they have already completely gone to seed. What I then do is harvest the seeds and keep them in an envelope for planting in the next spring instead of having annuals popping up all over the garden. I prefer to replant the seeds in the area of the garden where I want the annuals to grow.

To learn more about what to do with your flowering plants in the fall, check out this article: Cut Back, Compost, Or Continue? A Quick Guide To Fall Flower Clean Up. 

Are cut flowers compostable?

Most cut flowers are definitely compostable. This is especially true if we are talking about cut flowers from your garden that have now faded in their vase. Removing the faded flowers from the vase and composting them is an excellent excuse to cut fresh flowers to create a new arrangement in the vase.

Pulling faded blooms from your current vase will also help freshen up the arrangement, giving you an opportunity to change the water and trim the stems while you’re at it. 

When doing a new flower arrangement, there will always be trimmings from the flower stalks before putting the flowers into the water. These trimmings can also go into your compost bin as green waste.

In general, farmer’s market flower bouquets that have faded are also fine for adding to your compost. However, you should be vigilant for any ribbons or elastic bands holding the bouquet together, as you only want organic material in your compost bin. 

At my local farmer’s market, the flower seller gives people the option to take a sachet of flower food to add to the vase in order to make the flowers last longer. I never take the sachet of flower food as it contains an antibacterial chemical that can harm the microorganisms in my compost bin that helps the compost break down quickly.

If you want to read what I use for my flowers instead of commercial flower food, bookmark this article for a homemade recipe: How to Keep Cut Flowers Fresh: 7 Tips from the Pros.

Most of the time, I wouldn’t put store-bought flower bouquets into my compost bin as most of them have been treated with synthetic chemicals in order to increase the flowers’ vase life. Plus, chances are they’ve been grown with loads of herbicides, which isn’t something I want to introduce to my compost pile. 

Can I compost annuals?

You can compost almost all annuals, which form part of the greens waste in your compost system. If your annuals have already gone to seed, as sometimes happens to me, then harvest the seeds and keep them in an envelope for planting in the springtime. 

Most annuals, such as zinnias, cosmos, or snapdragons, can be composted whole. For flowers with thick or tough stems like sunflowers, cut those into smaller pieces first to speed up the decomposition. 

The only time I wouldn’t add annuals to my compost is if the plants had died from a disease that could contaminate my compost bin and future garden seasons. Those plants go in the garbage. 

For more specific information on what to do with your annuals when they’re finished blooming, bookmark this article: Annuals At The End Of The Season: Birds, Bugs, Or Compost. 

Can I compost perennials?

Perennials are excellent for the compost bin, which is handy considering you’ll most likely have trimmings from them every year when you cut them back. Bear in mind that the stems and branches of your perennials tend to be a lot woodier than what your annuals are. Cutting the branches into smaller pieces will help them decompose faster. 

Check which time of year you need to prune your perennials. Some types should be cut back in late summer after they’ve finished blooming, while others need to experience the first fall frost before you can cut off dead branches and dead flowers. 

In either case, before adding any perennial flowers to your compost bin, check to see that none of the flowers are diseased.

What flowers should not go in the compost pile?

They are certain flowers that I wouldn’t add to my compost. 

• Any plants that have been treated with any toxic herbicides or pesticides to prevent contamination.
• Flowers that are diseased or from a plant that is diseased to prevent the disease from spreading across the rest of my garden. Bulbs and thorny rose stems unless I can chop them down very small. Neither of these would be harmful to my compost; they just tend to take up to two years to decompose fully unless first shredded down to small pieces.

Finally, there is the category of toxic flowers that I wouldn’t add to my compost bin. These include the likes of Juniper, Walnut, Laurel, Eucalyptus, and Oleander. The toxins within these have the potential to render your compost toxic. I would stay clear of them, especially if you have young children. 

However, when it comes to oleander, there’s an interesting 2003 research paper showing how oleandrin decomposes within the compost. Oleandrin is the toxic compound found in oleander, and even mild exposure to the sap from the leaves or stems can cause severe skin irritation. 

In the study, it was found that while the oleander was decomposing, the levels of toxic oleandrin were reduced by 90% over the first 50 days of composting. By the time the oleander had been composting for 300 days, there was no longer any trace of toxic oleandrin detectable. 

For me, this is valuable information since I live in southern California, where oleanders commonly grow. We even have some oleanders in our side yard. 

Depending on where you live, you might have a native or regional plant that is typically on the no-no list for composting. Before you swear it off forever, it’s worth checking to see if the data has changed and if it can be a valuable part of your compost pile. 

Learn more

With that, your garden clean-up won’t just tidy up your garden. It will help it transition between seasons and prepare it for the next round of sowing. By composting your garden flowers, you’ll be one step close to creating a closed-loop system, building soil nutrition and health in your backyard. 

For more about garden chores and keeping your garden productive, check out these articles:

• How To Compost With Flowers: A Guide To Fall Clean Up
• What Do You Do With Annuals At The End Of The Season (Flower Garden Clean Up)