Dealing with big old shrubs, that yellow lawn weed, and plant bargains: This Weekend in the Garden

Nov 01, 2023

This redtwig dogwood looks like it's been pruned to death, but it's merely been "rejuvenated."

Removal isn't the only option for a big, old shrub that's outgrowing its space or just not blooming well anymore.

Many overgrown shrubs can be brought back into size and shape and even induced to bloom well again by a severe whack-back known as "rejuvenation pruning."

This involves cutting all of the shrub's shoots back to within four to eight inches of the ground, which usually stimulates the growth of more vigorous young shoots both from lower on the old shoots and from the base of the plant.

A more gradual variation is "renewal pruning," which removes a third of the old growth each year over three years, resulting in an all-new shrub by year four.

Although these severe cutbacks sound like they should finish off a struggling oldster, it usually does the opposite. Getting rid of old growth triggers dormant buds to spring into action and become the new "front line" responsible for growing leaves and keeping the plant alive.

Winterthur Gardens used this technique years ago on a large wooded area full of aged rhododendrons that had become leggy and lost flower power. Whacking everything down to ankle level resulted in denser, stockier plants that bloomed beautifully again in two to three years – without any removal or costly replanting.

You can't do this with all plants, though.

The best candidates are leaf-dropping (deciduous) flowering shrubs that have multiple stems, including red- and gold-twig shrub dogwoods, lilac, weigela, forsythia, willows, panicle hydrangea, rhododendron, elderberry, butterfly bush, smokebush, ninebark, mock orange, shrub roses, rose-of-sharon, privet, flowering quince, and most spireas and viburnums.

Don't try rejuvenation pruning on single-trunk trees or needled evergreens. A few may respond well, but most of these will either send up a host of weak shoots ("suckers") or die altogether.

Also avoid severe cutbacks on any plants that have been grafted onto rootstocks, i.e. most roses and fruit trees. Growth that's stimulated below the graft will come from the rootstock instead of the more desired grafted-on section (the "scion").

Rejuvenation pruning makes sense for any sentimental attachments as well as plants you like that are just out of control.

All of the cutting is hard work and generates a lot of wood waste, but it saves the cost of replacement plants and gives quicker results since the plants are regrowing from mature roots as opposed to starting from young roots.

Even if a rejuvenation fails, at least you tried to "save" the plant instead of going right to "dig and replace."

For sentimental plants, take a few branch-tip cuttings the year before rejuvenating so you’ll have rooted copies to plant in case the mother plant dies.

On the other hand, if you really don't like a plant even if it were fine size-wise and blooming well, then a shovel is the better weapon.

Now is a good time of year to do rejuvenation or renewal pruning on plants that bloom in spring (or that should have bloomed in spring).

End of winter or very early spring is a better time to prune summer bloomers, such as rose-of-sharon, panicle hydrangeas, and butterfly bush, since they flower on that season's growth.

The end-of-winter/early-spring time frame is also OK for spring bloomers... you’ll just sacrifice any flowers you would have had that year since these shrubs bloom on wood that grew last summer and fall.

To rejuvenate in one fell swoop, use a saw or loppers to cut all of the shoots back to four to eight inches above the ground.

Scatter the ground with a granular, balanced fertilizer after the debris has been removed (and ideally chipped into mulch). Then water well and add a fresh layer of shredded hardwood or bark mulch totaling two to third inches deep.

Soak the ground weekly during hot, dry spells in summer since the plant will be using extra resources to grow all of that new wood and foliage. It's also a good idea to soak the ground a day or two ahead of your whackback when it's been dry, such as May was.

If you’re uncertain whether your plant is up for this degree of challenge – or if your nerves aren't – fall back on the renewal option.

In year one, zero in on dead wood, diseased wood, crossing branches, and/or the biggest, oldest, gangliest, poorest-blooming wood. Remove about one-third of this wood right to the ground.

Watch for new shoots during the growing season.

In year two, cut back the next one-third of wood to the ground, and shorten any of last year's new shoots by up to one-third as desired.

In year three, cut back the remaining one-third of wood to the ground, and thin out and/or shorten any of the previous two years’ new shoots by up to one-third.

Extra watering, fresh mulch, and an annual dose of fertilizer also will help with recovery from renewal pruning.

In both of these situations, begin pruning annually once the cutback plants reach the desired size and shape. It's far better for the plant (and easier on you) to do regular light pruning than to let a plant grow way too gangly and then do battle with a leafy mammoth.

For more details on pruning woody plants, including rejuvenation pruning, see Purdue University's free, excellent, and nicely illustrated fact sheet "Pruning Ornamental Trees and Shrubs."

These little yellow flowers are those of birdsfoot trefoil growing in a lawn.

A late-spring lawn weed that seems to be gaining steam lately in Pennsylvania lawns is birdsfoot trefoil, a mat-former with little yellow flowers the size of small peas.

Not nearly as ingrained or as well known as the dandelion or even chickweed and purslane, birdsfoot trefoil arrived in America from Europe and Asia as a promising forage crop. It was planted as an alfalfa alternative for cattle feed in poor-soil sites.

However, as tough plants that seed well are prone to do, birdsfoot trefoil has moved from pastures and forage land to lawns, landscapes, and untended natural areas.

In lawns, plants stay a few inches tall since they’re being mowed. (They can grow upwards of three feet tall if not cut.)

Birdsfoot trefoil blooms primarily in June with buttony yellow flowers that look like mini buttercups.

Seeds then mature from July into August to spread the colony, although this is a perennial weed that also spreads by underground and surface runners.

"It's a relentless spreader where plant competition is wimpy or non-existent," says Ohio State Extension educator Joe Boggs on a post on birdsfoot trefoil, which is also fast becoming a common Ohio lawn weed.

Birdsfoot trefoil gets its name from the shape of its seed pods, which supposedly look like the clawed feet of birds.

The good news is that this plant is fairly easy to kill with any number of broadleaf herbicides sold for use in lawns, although it may take more than one application to kill an entire colony. Early-fall applications are especially effective.

On the other hand, the plant is a legume that adds nitrogen to the soil, making it both a grass feeder and a potential pollinator attractor if you view it more as a "volunteer plant" than a weed.

Garden centers often discount annual flowers and summer vegetables in June.

Still have a few empty spots in the landscape or vegetable garden?

It's not too late to fill in with a few more annual flowers or warm-weather vegetable transplants from the garden center or box store. You might even find some bargain prices.

Retailers often discount annual plants this time of year… after the May rush and before hot summer weather slows the shopping flow to a trickle.

Better to sell as many of them as possible at 50-percent markdowns than to have to toss them in another few weeks as they get leggy and pot-bound.

These discounted annuals are also good for adding spots of color to spring-peaking gardens that are just green in summer or for putting together an extra pot or two for a deck or patio.

Fray out the roots before planting because June-bought flowers and veggies usually have circling roots as a result of the longer-than-anticipated time in their nursery pots.

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