You’ve heard of annuals and perennials, but what is a biennial plant? While annuals can be a flash in the pan and perennials take an eternity to start blooming, true biennial plants take two years to complete their life cycle, occupying the sweet spot between fast growth and hardiness.
Some examples of biennials are delicious vegetables like beets, carrots, Swiss chard, and kale, as well as cheerful flowers like sweet William and forget-me-not. Discover which biennials you can grow in your garden and how to care for them.
What is a biennial plant?
Unlike annual plants that complete their entire life cycle in one year or perennial plants that live for three or more years, biennials have a two-year lifespan. These flowering plants spend their first year preparing for the “big show” in their second year.
Here’s a more in-depth look at what happens during the first and second year of a biennial plant’s life:
Year 1: Growth, structure, and vernalization
The initial year in the life of a biennial plant is a crucial phase characterized by distinctive features that set the stage for its future.
Growth patterns
In the first year of their intriguing two-year life cycle, biennials primarily focus on vegetative growth. This phase is crucial for establishing a strong foundation for future reproductive efforts.
During this initial period, biennials develop a rosette of leaves surrounding a low-growing stem, as well as an extensive root system that anchors them securely into the soil. Doing so ensures they have the necessary resources for the flowering and seed-setting phase in the subsequent year.
Leaf structure
The leaves of biennial plants in their first year often exhibit distinctive features. These can include variations in size, shape, and texture, depending on the specific species. Some biennials showcase leaves with intricate patterns, serrated edges, or unique arrangements that aid in optimal sunlight absorption and efficient photosynthesis.
The diversity in leaf structure during this stage adds visual interest to the garden, even before the spectacular display of flowers in the following year.
Vernalization
During the cold months, the plants turn brown and go dormant to overwinter. For a successful bloom the next year, biennials require prolonged exposure to cold temperatures, known as vernalization, between their first and second season. Cold temperatures give plants a seasonal calendar, so they know when to stay dormant and when it’s safe to grow.
Year 2: Flowering and seed production
In the second year of a biennial plant’s life, a remarkable transformation takes place as it shifts gears from vegetative growth to the crucial stages of reproduction.
Bolting and flowering
The second year marks a significant transition for biennial plants as they shift their energy from vegetative growth to reproduction. One notable phenomenon during this phase is “bolting,” where the plant rapidly elongates its stem. This vertical growth is accompanied by the development of flowering structures.
During summer, biennials unfurl breathtaking flowers and fruits, contributing vibrant colors and textures to the garden.
Seed formation
Following the extravagant display of flowers, biennials enter the crucial stage of seed production in the fall. As the flowers fade, seed pods or capsules begin to form, containing the next generation of plants. The meticulous design of these seed structures facilitates effective dispersal, allowing the seeds to find suitable locations for germination.
Once the seeds are mature and ready, they are released into the surrounding environment, completing the remarkable two-year life cycle.
Note: Just because biennials die after two years doesn’t mean you have to start from scratch with fresh seeds. Many biennials are highly successful self-seeders, releasing fresh seeds in the fall that germinate in spring to start the biennial cycle all over again. So, if you’re happy with a wilder, more natural aesthetic, you can let your biennials do the seeding work for you.
Best biennials for your garden
idunbarreid | Flickr | Public Domain
Most biennials are either vegetables or flowers. Here are some of the tastiest and most beautiful biennials for your veggie or flower garden:
| Popular biennials for a vegetable garden | Popular biennials for a flower garden |
| Beets | Black-eyed Susan |
| Broccoli | Canterbury bells |
| Brussels sprouts | Evening primrose |
| Carrots | Foxglove |
| Celery | Forget-me-not |
| Collards | Hollyhock |
| Dill | Lunaria (money plant) |
| Fennel | Scorpion grass |
| Kale | Stock |
| Onions | Sweet William |
| Parsley | |
| Rutabaga | |
| Swiss chard |
Note: You can grow black-eyed Susan either as a biennial or short-lived perennial.
Pros and cons of biennials
Biennials are typically hardier than annuals and faster to bloom than perennials, making them a beloved “middle child” for gardeners.
Pros of biennials
Here’s why biennials are a savvy choice for your garden:
✓ More cold-tolerant and drought-tolerant than annuals: While biennials aren’t as hardy as perennials, they’re better equipped to handle adverse weather conditions and cold climates than annuals. For example, Swiss chard is exceptionally drought-tolerant, and beets grow well in nutrient-poor soil.
✓ Excellent self-seeders: Most biennials readily reseed themselves, so you won’t have to worry about spreading new seeds every two years. Biennials will die in their second fall, but new seeds will start growing the next spring. Just be conscious of potential cross-pollination — next year’s harvest may look and taste different than your original vegetables.
✓ Lower-maintenance than annuals: Biennials need more frequent watering and fertilizer applications than perennials, but they don’t need as much TLC as annuals. While most annuals require fertilization every week or two weeks, tough biennials like Swiss chard, beets, and turnips can thrive with just one or two applications of fertilizer per season.
✓ Many veggie options: If you’re growing a vegetable garden, chances are you’re growing biennials. From broccoli to carrots to onions, there’s a biennial that’ll give you a delicious, sustainable harvest, saving you from grocery runs and decreasing your carbon footprint.
✓ Native, eco-friendly plant choices: Native biennials like black-eyed Susan and evening primrose provide food and shelter to threatened pollinators like butterflies, bees, and birds. Since these biennials are specifically adapted to North America, they require very little maintenance and no harmful chemicals.
Cons of biennials
A healthy garden should be composed mostly of perennials, supplemented by a mix of biennials and annuals. Here’s why you shouldn’t solely grow biennials in your yard:
✗ Not as hardy as perennials: Most biennials are native to the Mediterranean region and prefer temperatures between 50 and 70 degrees Fahrenheit. So, if you live in the Deep South or far up North, biennials can be tricky to grow.
✗ Fewer size options: Because biennials only live for two years, they don’t grow extremely high or wide. While some intrepid black-eyed Susans may grow as tall as 6 feet, you won’t find any biennial trees or hedges at your garden center.
✗ Only a handful of native species: While you can find native biennials, there aren’t nearly as many varieties as there are native perennials. For an eco-friendly xeriscape (low-water landscape), rain garden, or pollinator garden, you’ll need a majority of native perennials.
✗ Unpredictable life cycles: Some biennials may not survive their first winter, while others may bolt (complete their full life cycle in the first growing season), and still others may live longer than three years. It can be disappointing when a plant fails to produce fruit or rushes through its growing season too quickly for you to harvest mature fruits.
✗ Reseeding doesn’t guarantee evenness: Biennials generally self-seed, but that doesn’t mean they self-seed evenly. If you prefer a neat, linear garden aesthetic, you may want to collect seeds and hand-sow them or plant brand-new seeds instead of letting the wind plant your seeds for you.
Tips for growing biennials
Biennials may be hardier than annuals, but they still need TLC to grow strong for two years. Here are some tips for planting and maintaining your biennials:
- Order a soil test through your local cooperative extension service to determine what types of soil amendments you should add to your garden for optimal soil health and plant growth.
- Add a layer of compost (2 to 4 inches) into the soil. This is best done in the fall before the spring planting to give compost time to decompose and improve the soil.
- Plant most biennials in early spring as soon as the soil is workable to give the root system time to establish before summer. Check your biennials’ specific planting needs before sowing. Some warmer-weather biennials like sweet William and dill should be planted in late spring to early summer once the threat of frost has passed.
- Fertilize seeds or young plants with a fertilizer that fits their specific nitrogen, phosphorus, and potassium (N-P-K) needs. For example, celery benefits from a high-potassium fertilizer (4-4-8), whereas collards and other leafy greens require a high-nitrogen fertilizer (15-0-0) to enhance leaf production.
- Follow a fertilization schedule based on your biennial plants’ needs. Lunaria only needs one or two feedings of slow-release fertilizer per season, whereas onions need a high-nitrogen fertilizer every two to three weeks.
- Spread a healthy layer of organic mulch around young plants to protect their roots, keep the soil moist, and prevent weeds.
- Stake tall, top-heavy plants proactively before they start to flop over. Stakes should be 6 inches shorter than the mature plant so they don’t detract from the plant’s natural aesthetic.
- Weed your garden by hand once a week.
- Trim and prune plants to remove diseased leaves and scraggly stems.
- Deadhead spent flowers of biennials like foxgloves and sweet William throughout the growing season to redirect the plant’s energy from producing seed heads to growing fresh blossoms. Allow the last flowers of fall to set seed for fresh seedlings in the spring.
How to water your biennials
Water daily for the first two weeks after planting. Then, transition to watering once a week in the cool spring weather and up to three times per week in the summer heat. Keep the soil moist but not soggy, as wet soil can cause root rot.
Biennials typically need 1 to 1.5 inches of water per week, either from natural rainfall or irrigation. Water them deeply to encourage long, strong roots. Otherwise, shallow and frequent watering will encourage the roots to stay close to the soil surface, which quickly leads to root dehydration when a drought hits.
Water your biennials with a soaker hose or drip irrigation system instead of sprinklers to deliver water directly to the plant roots and minimize the amount of water lost to evaporation.
FAQ about biennial plants
Can I save seeds from a biennial plant to replant in the future?
Yes, collecting seeds after flowering in the second year allows for propagation and continuity in your garden.
Why does bolting occur?
Bolting occurs when a plant mistakes a temperature fluctuation for a change of season and behaves like an annual rather than a biennial in response. Bolting is typically caused by a string of cold days in spring or a particularly hot summer.
Bolting plants flower prematurely and experience their entire life cycle in one growing season (as little as three months), which can be disappointing for gardeners planning on a large harvest in the second year.
Can I make my biennial flowers bloom faster?
Yes. If you live in a cooler climate, you can “trick” certain biennial flowers like foxgloves and hollyhocks into flowering before the second summer. Sow the seeds in mid to late summer rather than spring. The cool fall and winter temperatures will induce flowering, and they will continue growing and flowering into spring.
Hire a pro to help grow and maintain your biennials
Now that you understand what a biennial plant is, you can start growing and harvesting them in your garden. But while it can be fun and fulfilling, sweaty garden tasks like fertilizing, pruning, and cleanup can take a big bite out of your weekend — when the only bites you want to take are out of your fresh veggies.Take the easy way and call a local lawn care pro to keep your garden and lawn in tip-top condition so you can fire up the grill and enjoy your harvest.
Main Photo Credit: MabelAmber | Pixabay
