The ultimate perennial guide

Perennials are beautiful and versatile plants that will fill your garden with interest for many years. Although often chosen for their stunning freedom flower color, perennials can also be planted for height, evergreen structure, fragrance, ground cover, and more. We asked experienced gardener Carol Bartlett to share her knowledge about growing these hard-working favorite plants. Here’s her tried-and-true advice…

Browse our full range of perennials for inspiration.

What are perennials?

Perennials are non-woody plants that persist for more than two years. Very popular, they come in all shapes and sizes, including tall, fragrant, climbing, winter blooming, and evergreen perennials. Most are cold hardy, but some are semi-hardy. Some are herbaceous and die back in late summer, eventually turning bare over the winter and producing fresh leaves in the spring.

If you’re looking for color in your garden, perennials offer a rainbow of colors from pale pastels to hot reds. These include bright red/orange/yellow crocosmia, hardy and dependable geraniums, tall spired home garden plants like lupins and delphiniums, long-flowering heleniums, bold coneflowers, and popular clematis. Contains garden favorites. Perennials are cost effective. Once planted, they will come back every year.

When and where to plant perennials

Alstroemeria blooms in patio containers from June to November.
Image: Alstroemeria ‘Indian Summer’ from T&M

Spring is traditionally considered the best time to plant perennials, but they can be planted any time from spring to late fall. Many perennials are sold as garden-ready plants during the summer, adding instant color to borders. Adequate watering is essential for new plants to establish, so perennials planted in the spring and summer require regular additional watering. Fall is an often ignored but ideal planting time. The soil is still warm and the rain is increasing.

Perennials are great for growing in borders or containers to add color and fragrance. Perennials that are great for containers include agapanthus, dahlias, lilies, and lavender. A large container of hostas also looks luxurious and stylish, especially when placed in a shady corner.

The key to successfully growing perennials is the right plant, right location. All perennials have favorable growing conditions, including full sun, partial sun, shade, water-retentive soil, or dry conditions. For a plant to thrive, it must be grown in a garden location that is most suitable for its growing conditions. If you’re not sure what your requirements are, check out our perennial resources page for information and advice.

How to plant perennials

This compact clematis is a hardy perennial perfect for patio containers.
Image: T&M’s Clematis ‘Guernsey Flute’™

As a rule of thumb, most perennials require humus-rich soil with good structure. Perennials, especially herbaceous perennials, are best planted in good soil because they expend a lot of energy each year growing and blooming. There are always exceptions. Lavender and nepeta, like Achillea, grow well in thin soil.

Here’s how to plant ready-to-use perennials in your garden.

Dig a hole slightly larger than the pot, about 5cm in circumference. Remove the perennial from the container and release the roots so that the plant is not compressed. Place it in a hole level with the garden soil. Backfill the hole and make sure there are no air pockets. When roots grow into air pockets, they are unable to draw in nutrients and water, and the plant may not be able to grow. Examine each plant to determine its height and spread. This will help you determine where to plant within the boundary and how close it will be to surrounding shrubs and perennials. Water, water, and more water.

There is one important exception. When planting clematis, plant them at a depth of about 10 cm from the soil surface. We recommend planting clematis a little deeper.

How and when to prune perennials

Nepeta’s fragrant silver-gray leaves are suitable for Chelsea chops
Image: Nepeta x faassenii from T&M

Herbaceous perennials can be pruned in the fall once the top growth has died back. Alternatively, you can leave the top growth alone to protect the plant (and the insects that winter in it) from frost, and prune it in the spring.

During the summer growing season, you can also cut back many perennials after they have finished flowering to encourage a second flush of fresh foliage and flowers. Ideal for this treatment are hardy geraniums, Alchemilla mollis, centaurea, lavender, heuchera and nepeta. Deadhead your perennials regularly to encourage new blooms throughout the season.

If you want your perennials to look bushier, you can also try Chelsea Chop. The Chelsea Chop, carried out in May, is a simple pruning of pre-flowering perennials, reducing the number of plants by about one-third. This light pruning will cause the plant to produce more buds. It is especially useful for plants that spread easily, such as Nepeta. You can vary the way you apply Chelsea Chop by cutting some plants and leaving others uncut. If you plant many of the same variety, the flowering times will be different. You can also cut back parts of the plant or chop the entire plant to reduce the height of the border. Adjust the techniques to your liking to get the most out of your perennials. Plants suitable for Chelsea chop include nepeta, asters, monarda, lavender, echinacea, artemisia, sedum, phlox, helianthus, and rudbeckia. As a guide, it is suitable for multi-stemmed perennials.

When and how to divide perennials

The root ball of Hemerocallis is large.
Image: Hemerocallis ‘See You Tomorrow’ in T&M (© Plantipp, Visions BV Netherlands)

Ideally, perennials should be divided every three years. If your plant isn’t flowering or has a bald spot in the middle, you’ll know it’s time to lift and divide the plant. The best time to divide perennials is spring or fall. Here’s what you need to do:

I always use a fork to lift the plants out of the ground to minimize damage to the roots. Inspect the roots. Because there are so many different types of plants, their roots also vary widely. For smaller plants, such as geraniums, you can pull the root ball apart by hand. Divide into 2-5 times depending on the size of the plant. For large plants like Hemerocallis, the roots can be very large. This type of root is best separated by placing two forks back to back and prying up the root ball. Larger plants with very strong, fibrous roots, such as agapanthus, require more force. Once you remove the plant from its container, use an old bread knife or handsaw to cut it into sections. It may seem cruel, but stocks can recover and improve after a split. Repot under suitable growing conditions and water thoroughly.

Carol Bartlett’s 5 Favorite Perennials

The ruffled flowers of L. ‘Crazy Daisy’ are one of Carol’s favorites
Image: Leucanthemum ‘Crazy Daisy’ from T&M

I love perennials and grow many of them in my garden for their color and fragrance. My favorites are:

I love daisies and I love bees, so it’s Leucanthemum. They are easy to grow and have a long flowering season, and I especially like the frilly-petaled varieties such as L. ‘Crazy Daisy’ Agapanthus. It features large, prickly flowers in bold shades of blue and white. Agapanthus grows well in containers, making them ideal for patios. Agapanthus also belong to a special group of plants that bloom for a long time and look beautiful even after their flowers fade. Geraniums are garden powerhouses that reliably bloom year after year. Available in a variety of sizes and colors, you can find varieties that tolerate almost any growing condition. In my garden, there is always room for geraniums from summer until October. Sedum is a perennial that blooms from late summer to fall. I have never had a garden without sedums. I love the rosy red and white varieties, which are wildlife friendly and attract butterflies and pollinators. Lavender is appealing for its intense blue hue and calming scent. I like to plant lavender next to a path for perfume or on my patio so I can reach out and touch the tactile, wonderfully scented flowers.

We hope this article will help you choose and plant perennials. Check out our top 10 perennials for more inspiration. For a satisfying challenge, you might consider sowing your own perennial seeds.

Carol Bartlett has been gardening for over 30 years and has created many different types of gardens. Her website, The Sunday Gardener, was founded over 10 years ago to provide practical, down-to-earth advice, especially for novice gardeners, no matter the size of their garden or vegetable plot. She also aims to inspire others to enjoy gardening and enjoy the benefits of being outdoors and with nature.

Carol writes the information for the website herself and most of the images are taken in her garden or places she visits. The idea is to display plants in a real garden environment. Her philosophy is that gardening is a great combination of therapy and practice. Although it’s a cliché, it’s true that a garden is a haven from the pressures of everyday life. You can follow Carol on Facebook and Instagram and watch her helpful videos on YouTube.

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