Pruning and Deadheading: The Two Habits That Keep Perennial Gardens Thriving
Pruning removes growth that is too large or that is broken off․ This keeps plants within bounds and directs their energy․ Deadheading removes flowers that have faded․ This keeps the plant from going to seed and‚ in many cases‚ encourages the plant to flower more․ Pruning and deadheading are the difference between a perennial bed that is tired and spent by July versus one that is still doing fine in September․ But skip a year or two and you will see the leggy stems and the fewer flowers and the plants that seed themselves where you never intended them to․
While much of Tennessee is in USDA zone 6b to 7b‚ timing is still relevant․ A late fall pruning cut may take off young foliage, which will be killed by an early frost․ Trim too heavily in September, and you may be taking away seed heads needed by late fall pollinators․ Having the timing down takes some of the guesswork out of the picture․
Deadheading: a small task that pays off․
Deadheading is the simple removal of a flower after it has faded but before it has produced seed․ In most cases‚ deadheading perennials involves more than just pinching off the heads; the stem should be cut just above the next pair of leaves or the lateral bud․ That is not the same as a person becoming a naked stub‚ which can rot through Tennessee's summer humidity․
Plants such as coreopsis‚ salvia‚ and shasta daisies do have a true second bloom 2 to 3 weeks after being deadheaded․ Others‚ such as peonies and bearded iris‚ have no chance of a second bloom in the same year regardless of deadheading‚ but the plant can still benefit because energy once used to ripen seed pods can be redirected into the root system‚ improving next year's performance․
One thing I should mention that somehow people with more general advice on this topic forget is that not every perennial is better off after being deadheaded․ Coneflowers and black-eyed Susans are good examples of plants that you want to leave alone towards the end of the growing season․ The seed heads will feed goldfinches and other fall and winter visitors․ If you leave the seed heads standing and fall is over‚ by December they will likely be stripped off by the birds․ Deadhead early on in summer but leave the last heads to go to seed by late August․
Pruning: More Than Just Cutting Back
Pruning of perennials can be divided into a few categories․ The most common should be referred to as pinching․ In late spring when the new growth appears on certain perennials such as garden phlox or asters‚ these plants are pruned back a few inches to maintain a more compact shape․ This forces the plant to branch out lower‚ and results in a bushier plant that is less likely to fall over by midsummer․ It is a small sacrifice of height for a much better-looking plant later․
Mid-season pruning is also a rescue operation․ If your catmint or salvia has grown lanky and scraggly by July (and it will in Tennessee when the thermometer hits a steady 90)‚ tear it back by a third to a half in height․ In two to three weeks, new basal growth usually appears, and often another flush of flowers will follow in the fall․
Then‚ the big fall or late-winter cutback‚ where you cut back the dead foliage and the spent stems to a few inches above the crown․ In Middle and East Tennessee‚ most gardeners tend to wait until after the first hard frost‚ which comes about mid- to late-October․ Early cuts risk removing structures needed to produce the energy and food for the plant to go dormant through winter․ Some gardeners leave stems through winter for both structure and animal habitat‚ cutting down in late February‚ just before active growth begins․ Any of these approaches are acceptable․ Just don't do it twice․
Tools and Technique Actually Matter
Most plant injury in home gardens happens to be due to using a dull tool rather than pruning at the wrong time of year․ When pruning‚ use sharp‚ clean-bladed bypass pruners instead of anvil-style (like scissors) pruning shears․ When working around plants with any signs of fungal disease‚ you're better off wiping your blades with rubbing alcohol between plants․ It saves more plants than you'd think․ A ragged or pounded cut just heals that much slower‚ and offers easy entry to pathogens‚ especially during humid summers in the Southeastern United States when powdery mildew and botrytis are common․
Cut just above the leaf node‚ leaving about a quarter inch above it․ If cut too far above‚ an unnecessary stub is created; over time‚ this will die back and can rot the healthy portion of the stem․ Cutting too closely may damage the bud itself․
Building a Garden That Needs Less of This
Perennials that may need a fair amount of maintenance in early years may become easier as they mature․ Blue Flag Iris does not need to have dead flowers removed as aggressively to continue blooming‚ nor does it need to be pruned as aggressively as it is a clumping plant․ Blue Lobelia is also untroubled by poor drainage or heavy clay soil‚ which is found in many parts of Tennessee‚ needing nothing more than a good shear after its first cluster of flowers․
For gardeners looking to add to or start a perennial bed‚ TN Nursery offers a Perennial Package with Purple & Gold Perennials․ The package contains plants that are compatible in both looks and care so that you will not be stuck with a range of pruning schedules in the same bed․
The Bottom Line
No one's going to win any beauty contests for pruning or deadheading‚ but it is the maintenance that makes the most difference in how a perennial bed looks and performs during the season․ Even a garden that gets thirty minutes of attention every couple of weeks during the season will always do better than one that's left alone and then hacked back all at once in fall․ Once you figure out what all the plants in your bed really want‚ some want to be cut hard‚ some barely want to be touched‚ the rest is easy․
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