Title Image

Perennial Care

Perennial Care

Perennial Care

Understanding Perennial Care

Perennials are the foundation of many beautiful gardens, blooming and looking lush year after year. Unlike annuals which complete their life cycle in one season, perennials come back for several seasons, regrowing from the roots each spring. This is why they are so valuable in any garden, giving continuity and long-term beauty with minimal maintenance. But to keep perennials thriving and looking their best they need specific care practices tailored to their growth habits.

Perennial care is about understanding the needs of each plant species, from soil type and sun requirements to watering and fertilizing schedules. Regular maintenance tasks like deadheading spent blooms, dividing crowded clumps and protecting from pests and diseases are key to keeping perennials healthy and happy. By investing a little time and effort in perennial care you can have a garden full of colour and life for years to come.

Water

All plants need some amount of water to live, but they don’t all require the same amount. By choosing plants that prefer the conditions you have, and by grouping plants in the garden by watering preferences, you make watering easier on yourself. If you do not use an automatic sprinkling system, have regional watering restrictions, or simply do not want to water your garden regularly, choose perennials that need less water to thrive.

Perennials that need less water:

  • Yarrow – Achillea
  • Anise Hyssop – Agastache
  • Ornamental Onion – Allium
  • Pinks – Dianthus
  • Coneflower – Echinacea
  • Baby’s Breath – Gypsophila
  • Red Hot Poker – Kniphofia
  • Lavender – Lavandula
  • Catmint – Nepeta
  • Beardtongue – Penstemon
  • Russian Sage – Perovskia
  • Perennial Salvia – Salvia
  • Stonecrop – Sedum
  • Switch Grass – Panicum (ornamental grass)

Perennials that prefer average to consistent amounts of water:

  • Japanese Anemone – Anemone
  • Goat’s Beard – Aruncus
  • Astilbe
  • Japanese Painted Fern – Athyrium
  • Heartleaf Brunnera – Brunnera
  • Clematis
  • Ferns
  • Cranesbill – Geranium
  • False Sunflower – Heliopsis
  • Daylilies – Hemerocallis
  • Coral Bells – Heuchera
  • Foamy Bells – Heucherella
  • Rose Mallow – Hibiscus 
  • Hosta
  • Shasta Daisy – Leucanthemum
  • Ligularia
  • Bee Balm – Monarda- Bergamot
  • Phlox
  • Jacob’s Ladder – Polemonium
  • Lungwort – Pulmonaria
  • Salvia
  • Foamflower – Tiarella
  • Spike Speedwell – Veronica
  • Fountain Grass – Pennisetum (ornamental grass)

Perennial Care – Deadheading Perennials

Deadheading is the simple act of removing the spent flowers from a plant before it goes to seed. In nature, seeds are an attempt to ensure that the next generation of plants develops. In some cases, once seeds have been produced, the plant will stop blooming since there is no reason to put energy into blooming anymore.

See also  The SGD Awards: A Garden Jewel in Dulwich

Not all perennials produce seeds. In such cases, we deadhead the plants to encourage more flowers to bloom. It won’t harm the plant at all if we choose not to deadhead—it is a matter of personal preference, not survivability.

When you deadhead, cut the stems down by about one-third or to the top of the mound of foliage if the flowers are produced at the tips of leafy stalks. Daisies, Bergamot (bee balm) and catmint are some examples of this. Watch for small buds forming along the length of the stems and be sure not to cut those off when you are deadheading these kinds of perennials. If the flowers are produced on their own stalks with no or few leaves, like daylilies and coral bells, remove the entire spent flower stalk.

Deadhead these perennials to encourage rebloom

  • Achillea
  • Clematis
  • Dianthus
  • Heliopsis
  • Hemerocallis
  • Kniphofia
  • Lavandula
  • Leucanthemum
  • Nepeta
  • Phlox
  • Salvia

Deadhead these perennials for appearance only (rebloom not likely)

  • Ornamental onion – Allium
  • Japanese anemone – Anemone
  • Goat’s beard – Aruncus
  • Astilbe
  • Heartleaf Brunnera – Brunnera
  • Cranesbill/Hardy geranium – Geranium
  • Non-reblooming daylilies – Hemerocallis
  • Coral bells – Heuchera
  • Foamy bells – Heucherella
  • Rose Mallow – Hibiscus
  • Hosta
  • Ligularia
  • Beardtongue – Penstemon
  • Russian sage – Perovskia
  • Creeping phlox – Phlox subulata
  • Lungwort – Pulmonaria
  • Stonecrop – Sedum
  • Foamflower – Tiarella
  • Spike Speedwell – Veronica

These perennials will develop interesting seed heads if you do not deadhead them:

  • Coneflower – Echinacea (leave standing to feed birds)
  • Clematis
  • Ornamental grasses

Perennial Care – Fertilising Perennials

Perennials and shrubs need far less fertilizer than flowering annual plants. Think about how these kinds of plants grow in nature. When perennials die back naturally for winter, their leaves fall at their feet and eventually disintegrate into humus, which in turn provides the nutrients they need to continue to grow.
To mimic that natural process, feed your perennials in early spring when new growth begins by spreading a thin layer or scattering handfuls of compost, humus, manure, shredded leaves, worm castings, or other organic ingredients on top of your garden beds. Through the seasons, the worms in your garden and rainstorms will filter those nutrients down into the ground where the plant’s roots can absorb them.

Some plants grow better in lean soil, meaning soil that is low in nutrients. Such plants can have weaker stems and become floppy if they are grown in soil that is too nutrient-rich. If you have lean soil, consider growing the perennials listed below.

Perennials that grow better in lean soils with little fertilizer

  • Yarrow – Achillea
  • Anise hyssop – Agastache
  • Red hot poker – Kniphofia
  • Lavender – Lavandula
  • Catmint – Nepeta
  • Beardtongue – Penstemon
  • Russian sage – Perovskia
  • Creeping phlox – Phlox subulata
  • Salvia
  • Stonecrop – Sedum
  • Ornamental grasses
See also  September thoughts

Cutting back perennials

Late autumn through to mid-winter. is the time of year when many people clean up their garden beds in preparation for winter. It is your choice whether to cut back your plants in fall or spring, but there are a few guidelines you’ll want to keep in mind before you decide.

Cut these perennials back in the autumn

  • Any perennials you do not want to reseed in your garden
  • Any perennials with diseased foliage, like powdery mildew, rust or leaf spot. Cut all of the foliage down to the ground and dispose of it rather than putting it on your compost pile.
  • Perennials that have heavy insect damage, like slug damaged Hostas. Bugs may lay their eggs in the spent foliage of their favourite plants, so by cleaning it out of the garden in fall, you are limiting pest issues the following year.

Don’t cut these perennials back in fall

  • Evergreen or semi-evergreen perennials like pinks (Dianthus), coral bells (Heuchera), foamy bells (Heucherella), foamflower (Tiarella), creeping phlox (Phlox subulata), bugleweed (Ajuga), Winter roses (Helleborus) and red-hot poker (Kniphofia)
  • Perennials with woody or hollow stems like rose mallow (Hibiscus) shown here, Russian sage (Perovskia), lavender (Lavandula), butterfly bush (Buddleia) and delphiniums
  • Perennials with winter interest coneflowers (Echinacea), ornamental grasses, autumn stonecrop (Sedum), and ornamental onion (Allium)

Perennial Care – Dividing Perennials

Some perennials grow so quickly that they benefit from being divided every 3-5 years to retain their vigour and flower power. Ornamental grasses, daylilies, irises and stonecrop are some examples. Other perennials, like coral bells and rose mallow, stay in a single clump that never needs to be divided. We’ll list some more examples for you below.

It is best NOT to divide plants with woody crowns, a single stem/crown, fragile fleshy roots, or a tap root as doing so can damage the plant. This includes:

  • Heartleaf brunnera – Brunnera
  • Clematis
  • Baby’s breath – Gypsophila
  • Coral bells – Heuchera
  • Foamy bells – Heucherella
  • Rose mallow – Hibiscus
  • Red hot poker – Kniphofia
  • Lavender – Lavandula
  • Beardtongue – Penstemon- Bergamot
  • Russian sage – Perovskia

Perennials with fibrous or loose root systems are the easiest kind to divide. Siberian irises, for example, can often be pulled apart with your hands once you’ve dug them up and shaken the soil off the roots. Helleborus are a little tougher to pull apart but can be cut with a sharp knife. Bergamot and Veronica are also easy to divide with a knife.

As a general guideline, perennials should be divided into the opposite season in which they bloom. That means if they bloom early in the season they should be divided in fall, and if they bloom late they should be divided in spring. When you do so, dig up the whole clump of the perennial you want to divide so you can easily see its root system. Each piece you pull or cut away from the original clump should be no smaller than what would fit in a 1ltr pot. Immediately replant the divided pieces into the garden or containers before their roots dry out.