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Ask Mr. Sage: How Should I Prune my Salvias?

Ask Mr. Sage: How Should I Prune my Salvias?
Category: Ask Mr. Sage

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Synopsis: Flowers by the Sea Online Nursery specializes in Salvias and often receives questions about how to prune them. Although getting good at pruning takes practice, Salvias rebound quickly if you make mistakes. A key to successful pruning is understanding the varying needs of four main categories of sages. Ask Mr. Sage is a regular feature of the FBTS Everything Salvias Blog.

Dear Mr. Sage,
I live in Santa Barbara and began growing Salvias last year, including Autumn Sage, Mexican Bush Sage and Hummingbird Sage. They all seem to grow easily here. I have a limited amount of time for gardening and need no-fuss plants. But here's my problem: I know that some pruning is necessary, but haven't got a clue when and how much to trim. In fact, I've been so busy that I've never pruned them at all. What should I do?

Also, I know that some Autumn Sages can survive cold winters. I want to suggest them to my sister in Kansas, but don't know what to tell her about pruning.

Regards,
Busy First-Time Salvia Gardener

Dear Busy Gardener,
Many Salvias are easy-care plants. Although getting good at pruning takes practice, Salvias rebound quickly if you make mistakes. This is especially true if you live in a warm winter area like Santa Barbara that is mostly in USDA Plant Hardiness Zones 9 and 10.

Whether in a mild coastal climate or the Midwest where freezing winter weather is common, deadheading (removal of faded blossoms) during the growing season is the most basic pruning practice that improves the health and appearance of any Salvia. However, pruning -- cutting back stems for healthy plant growth and good bloom -- requires understanding the four main categories of sages. These are:

  • Rosette-growing, herbaceous perennials
  • Deciduous or semi-evergreen types with soft stems
  • Deciduous, woody-stem varieties and
  • Evergreen, woody species.

Before I explain each type, it's important to note that each plant listing in the Flowers by the Sea online catalog includes a tab identifying its pruning category and basic pruning information.

Rosette Types

Erect flower stems rise from low mounds of foliage forming a rosette at the base of soft, herbaceous perennials.

Hummingbird Sage (Salvia spathacea) is a variety that blooms from winter to spring in Zone 8 and warmer climates. However, not all rosette-type Salvias are winter bloomers. Red Veined Sage (S. haematodes) is a variety that is hardy to Zone 3 and blooms spring into summer. Your sister might like this one.

During bloom time, completely remove any flowering stems of rosette sages after they become spent, which means they stop blooming and begin going to seed. This may lead to another round of flowering before the plant slows down for dormancy.

Dormancy may begin in summer for a winter bloomer. In contrast, a summer-flowering herbaceous perennial goes dormant in autumn. After frost or when growth comes to a halt, it's time to cut to ground any remaining flower stems.

Leaving some spent flowers to form seeds is good for hungry songbirds, but takes some energy away from strengthening roots for the next growing season. This is true for sages in all four pruning categories.

Deciduous or Semi-Evergreen with Soft Stems

This type of sage doesn't have woody growth. It may be a hardy type -- returning year after year in areas where its roots can survive winter temperatures -- or a tender perennial that usually is planted as an annual. Either way, its foliage dies to ground or becomes scraggly by the end of growing season.

Mexican Bush Sage (S. leucantha) fits in this category. It grows large rapidly and has numerous flowering stems that are long. Of the three types of Salvias you mentioned, this one presents the greatest challenge if not pruned during the flowering season and at dormancy.

Pruning deciduous or semi-evergreen sages during the growing season involves cutting to ground unsightly stems that have finished blooming. In mild-climate areas, growth of these sages can be particularly fast. When appearance becomes messy during the growing season, it's okay to give this kind of sage what we call a "haircut." Trim it back to a few inches above the ground. Then you can expect fresh growth and, most likely, a new period of flowering.

Dormant-season pruning should be done by first frost. Completely prune off the spent stems to avoid a tangled mess the next spring and to control pests over winter.

Deciduous, Woody-Stem Salvias

Autumn Sages (S. greggii species) are examples of woody-stemmed Salvias. They generally die back to ground in cold winter regions. In warmer climates, they may become shrub-like.

During the growing season, completely or partially removing spent stems stimulates new growth and flowering.

Despite their common name, S. greggii may bloom from spring to autumn. If you like a tidy fall cleanup in the garden following last bloom, cut spent stems to ground after first frost.

However, here's where we get to your question about how your sister in Kansas should prune Autumn sage: Gardeners in colder winter areas often say that plant survival improves if dormant season pruning leaves about 3 to 6 inches of deciduous woody stems. In spring, it's best to cut these remaining stems to ground to encourage vigorous growth.

Evergreen, Woody Salvias

In the right location, some Salvias are so woody and evergreen that we identify them as shrubs. These are sages that grow in warm-winter climates, including coastal areas in zones 8 to 11. A tall one that might do well in Santa Barbara is Karwinski's Sage (S. karwinskii), which grows up to 120 inches tall and 48 inches wide when in bloom.

Pruning of shrubby Salvias is the same year-round. Removal of old wood can occur at any time and encourages fresh growth. The process also involves shaping these large sages to control height, width and attractive appearance.

Pruning Tools and Videos

At FBTS, we use well-honed needle-nose pruners for fine stems and heavier duty anvil-blade models for thicker stems. Clean, sharp cuts are healthiest for plants.

If you would like to view FBTS videos about pruning, please visit the Views from the Garden section of our Everything Salvias Blog. For further questions about pruning or anything to do with Salvia gardening, please feel free to call or send us a note. We'll help you do it right.

Thanks for your question,
Mr. Sage