Pruning Salvias

This blog is based on notes I prepared for my interview with Tony Murrell on The Home and Garden Show, Radiolive 24th February 2018. Tony and I were discussing caring for Salvias, and in particular pruning to shape and how long to leave flowers on before trimming to encourage more to form.  There’s always so much more to discuss than we have time for on the radio, so below is my extended version of advice on this subject.
 

Salvias are fantastic plants – whether you’ve got a hot dry Mediterranean type garden or a shady, damp woodland area, there’s a Salvia for virtually every spot in your garden.
 
When we’re talking about caring for Salvias, and in particular pruning, it’s easiest to divide them into 3 specific groups.
 
Woody stemmed Salvias
These are shrubby types, they can be low growing or can get quite large. Salvia greggii and microphylla hybrids are the most well known, and gardeners will be familiar with the Glare series and more recently the So Cool series, as examples of this type. Others in NZ are those that originate from South Africa, like Salvia ‘African Skies’, S. aurea (previously S. africana-lutea), and S. lanceolata.
 
Generally they flower from late spring until late autumn in New Zealand, so it’s hard to know when to trim or prune them.  Because they flower for so long they can easily become woody and straggly.
To maintain the shape and encourage bushy growth and more flowers, lightly trim or tip prune a couple of times over summer.  If you want to keep flowers showing during this process, then trim only the second or third flowering stem back to the first obvious set of leaves. Next time around do the stems that were left from the first pruning. 
 
Or if you don’t mind the slightly bare look for a couple of weeks then you can do it the quick way and use hedge trimmers – don’t worry that you’re cutting flowers off, plants will soon recover. Aim to create a nice rounded shape, slightly higher in the middle than at the edges of the bush. At the end of autumn give the bush a better prune by about half, again aiming for that rounded shape.
 
Deciduous Herbaceous Salvias
 
Sounds like a mouthful but really it just means those plants that shoot direct from the base, but can in some cases reach great heights and can develop woody stems throughout the growing season. Then all the leaves fall off in winter leaving bare stems.
 
Examples are Salvia mexicana ‘Limelight’, S.elegans the Pineapple sage, S. ‘Waverly’, S. leucantha the Mexican bush sage and S. ‘Indigo Spires’.
 
Flowering times vary greatly in this group but to maintain the best shape I recommend tip-pruning after the first flush of flowers.  This often encourages the plant to produce a second flush of flowers and it’s after this that the timing of the main annual pruning becomes extremely important….and observation is the key.  Only prune the plant back to ground level if new growth is showing at the base. Otherwise you will kill it.
In frost-free areas this may mean that the main pruning can be done at any stage in autumn as new growth happens more readily in warmer climates. In cooler regions you might be best to wait until spring before pruning, but if the plant is very tall you can trim the stems back by about half until new growth shows in the spring. If you get frosts then you will need to mulch and cover the base of the plant as well.
 
Herbaceous Perennial Salvias
 
These types form a rosette or clump of leaves at ground level, then send up flower stems from the base.  Some are evergreen, some winter-dormant.
 
Examples are Salvia nemorosa, Salvia x superba or S. x sylvestris and their hybrids such as ‘Caradonna’, ‘Rose Queen’ and ‘Mainacht’; Salvia verticillata, S. transsylvanica ‘Blue Cloud’ and S. pratensis or Meadow Sage are other examples.
 
Caring for these Salvias is slightly easier. In spring simply tidy up any old leaves from around the base of the plant to get rid of any overwintering bugs and unsightly brown leaves, then once the first flush of flowers has finished, cut the spent flower stems back to ground level. Most will send up more flower stems and these can be cut back to the ground again when finished in the autumn.
 
Annual Salvias:  The focus on the topic of pruning today was mostly about perennials, but no doubt many gardeners will also be growing annual Salvias as well (or bedding Salvias). These are marketed under a variety of names in NZ and whilst some are genuine annuals, many are short-lived perennials that are frost tender, so grow them in pots, or take cuttings in early autumn.
 
Examples include Salvia farinacea, such as ‘Blue Bedder’, ‘Select Blue’; Salvia splendens types, such as ‘Purple Lighthouse’, ‘Red Velvet’, ‘Van Houtei’. Plus Salvia coccinea varieties like ‘Brenthurst’, ‘Lady in Red’ and ‘Snow Nymph’.
 
These varieties need regular tip pruning to keep them bushy and to keep the flowers coming. As with any plant if you let them set seed they frequently feel like they’ve done their job and don’t flower as well, so the trick is to keep them dead-headed.

click here to listen to the Radiolive interview