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Soil Preparation

Good soil preparation is the key to success with perennials since they will occupy their spot in the garden for several years. Most perennials prefer a well-drained soil that is high in organic matter. With heavy soils that may drain poorly, you may consider raising the area to improve drainage. For heavy or light soils, incorporating garden compost, well-rotted manure or peat into the top 8 to 12 inches will increase the organic matter and aid in drainage and soil aeration.

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Fertilizing

With proper soil preparation and improvement before planting, most perennials require little additional fertilization. Application of a ‘starter’ fertilizer when perennials are first planted may aid in more rapid establishment of the root system. For established plants, an annual application of a balanced, slow release fertilizer can be beneficial. Fertilizers high in nitrogen should not be used as nitrogen promotes excessive foliage production at the expense of producing flowers and a strong root system. Apply fertilizer so it does not come in contact with the leaves, as it may scorch them.

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Watering

Although water requirements for perennials can vary greatly from species to species, most require supplemental watering until well established. 1-inch of water a week is suitable for plant establishment. Once established, many perennials will require watering only during prolonged dry periods. Watering should be deep, infrequent and applied directly to the soil. This type of watering will promote deep rooting and will help reduce leaf diseases.

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Mulching

Organic mulches, such as wood chips, shredded bark, cocoa bean hulls or leaves, are beneficial in many ways. They help provide a cool, moist soil that perennials prefer, help to reduce weeds, allow perennials to spread, and help in overwintering by reducing frost penetration into the soil. For winter, a 4 to 6” mulch of leaves, marsh hay or straw will provide protection for shallow rooted perennials like mums, shasta daisies, delphiniums, etc. Rock mulches restrict the spreading of perennials.

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Staking

Exposure to wind varies with the site. Thought should be given to staking, particularly if growing taller perennials such as delphinium or lilies on windy sites. It is best to stake plants when they are first sending growth up because smaller plants are easier to work with and less likely to be damaged by staking. Staking early is also more aesthetically pleasing because new plant growth will cover the stakes. A stake two-thirds as high as the stem’s mature height should be pushed into the ground near the base of the shoot. Be careful not to harm the plant’s roots. Secure the shoot to the stake using twine.

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Flowering

Thinning dead and damaged shoots during the early stages of growth encourages stronger and healthier shoots. In late spring or early summer, when the plant is about one-third of its mature height, pinching can be done to increase flower development and encourage side shoot development. Pinching back new growth will help produce bushier plants which are less likely to require staking. Unless seed heads are used for winter decoration or seed is to be collected from them, flowers should be removed when they begin to fade. Deadheading may also promote additional flowering.

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Weeding

Hand weeding reduces competition for water and soil nutrients. If herbicides are used, do so carefully, as not to harm the perennial flowers.

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Dividing Perennials

Many perennials benefit from being divided periodically. If permitted to go undivided, they become crowded, lose their vigor and become vulnerable to diseases. Iris, daylilies and lilies are some of the perennials that benefit from being divided about every three years. Other perennials may never need dividing. Consult your local garden center if you are unsure as to what varieties need dividing. View our Dividing Perennials page for detailed information.

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Fall Cleanup

Once perennial plants have finished growing in the fall, cut the shoots down to the base (or leave 2 to 6-inches) and remove the debris. For plants that have some winter aesthetic value, cleanup can be left until spring.

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Winter Protection

Perennials damaged or killed during the winter usually are not injured directly by cold temperatures, but rather by rapidly fluctuating soil temperatures known as frost heaving. Frost heaving occurs when the soil alternately freezes and thaws, resulting in damage to the dormant crown and root system. Mulching in late fall with wood chips, pine needles, clean straw or other loose materials will help stop frost heaving. Do not use tree leaves or grass clippings as they may compact around the plant. Winter mulches should be applied after the ground freezes, usually in late November, and removed in early to mid-March.

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