Landscape plants not growing? Here’s why and what to do about it - pennlive.com

Oct 31, 2024

Plants like this azalea that are struggling to grow might be facing soil or siting trouble that need to be addressed.George Weigel

If your trees, shrubs, and evergreens seem to be the same size now as when the season started – or worse yet, are spindlier or deteriorated – a rescue venture might be on your 2025 gardening horizon.

Granted, 2024 wasn’t the best growing season with its unrelenting stretches of sizzling 90-degree days and spotty rains.

But if you watered reasonably well and still got no results, something deeper could be at play. That’s especially likely with plants that have been going nowhere (“sulking”) since the day you planted them.

Two underlying issues usually explain why landscape plants fail to thrive.

One is atrocious soil.

Many housing developments have compacted "builder's soil" that was heavily graded and then topped with a thin layer of topsoil.George Weigel

So many central Pennsylvania yards are full of heavy, compacted clay soil – or in the case of housing developments, a blend of clay, shale, and subsoil that was spread in a four- to six-inch layer over top of packed, graded subsoil during home construction.

This compacted layer is death waiting to happen for all but the most abuse-tolerant species – barberries, ornamental grasses, yews, junipers, daylilies, and the rest of the common short list that landscapers with replacement guarantees have learned to bank on.

If you don’t loosen and improve your death trap before planting with a heaping helping of compost, rotted leaves, or similar organic matter, most plants will never thrive. They’ll stunt, rot in poor drainage during wet weather, die during droughts because their roots haven’t penetrated the concrete-like “soil,” become more vulnerable to bugs and disease, and/or limp along in slow-death mode.

The second failure-to-thrive scenario is plants in the wrong spot.

Unbeknownst to many a rookie DIYer, you can’t just put any plant anywhere you think it might look good.

Sun-loving plants that end up in too much shade will never thrive or never bloom.

Shade-preferring plants in too much sun will bleach, brown around the leaf edges, and/or possibly die from excess heat and light.

Plants that prefer damp soil will wilt and die on a sunny bank, while drought-tough species will root-rot in low-lying areas of the yard.

That’s why it’s so important to put in the homework upfront to match plants to the setting you have.

This mass of tree "feeder roots" was filling the space where a struggling plant (now removed) had been trying to grow.George Weigel

A grossly underrated issue with plant placement involves planting near big trees.

The problem isn’t so much with shade from the canopy as it is with the roots underneath. The roots that most trees produce can easily out-compete surrounding plants for nutrients and moisture, especially when those other plants are inserted after the tree has a years-long head start.

In general, the bigger the tree, the more competition its roots dole out. Don’t underestimate the plant-stunting reach of those roots because most trees send out roots two to three times as wide as the branch canopy above.

On top of that, some tree species produce natural chemicals that stunt the growth of competitors. The best known is how the juglone in walnut trees is harmful and even fatal to hydrangeas, rhododendrons, yews, and other sensitive species.

Contributing to both bad soil and bad plant selection is the increasingly erratic weather that seems to be our new norm.

Temperatures above the upper 80s are detrimental to many of our traditional landscape plants, and those swings between spot droughts and heavy downpours make it tough for plants to generate season-long sustained growth.

That kind of punishing weather only exacerbates the two underlying main problems.

Now before we get into what you can do now, let’s knock down two courses of action that aren’t likely to help (unfortunately, ones that people tend to gravitate toward first).

Myth 1: Fertilize. Gardeners (and some pros) often look at fertilizers as a kind of medicine or stimulant that will perk up a struggling plant.

The inconvenient truth is that fertilizers aren’t panaceas but packages of nutrients that help only when plants are lacking those particular nutrients.

Most of the time, our soils have adequate amounts of key nutrients. More isn’t useful and could even harm plants via excess amounts or by throwing off what was a good nutrient balance.

Assuming the real problem is poor-quality compacted soil or a wrong plant in the wrong place, you’re barking up the wrong tree by blindly investing in fertilizer.

Before fertilizing “just in case,” a more sensible option is to test the soil, see if anything is lacking that could explain poor growth, and then apply a fertilizer of that specific kind in the right amount. Otherwise, you’re guessing.

Basic DIY soil tests by Penn State University’s Agricultural Analytical Services Lab are available at county Extension offices, most garden centers, and online directly from the lab for $10.

Struggling plants seldom overcome soil and siting troubles. More likely is a slow slide into plant death.George Weigel

Myth 2: Wait out the problem. It’s not only easier to do nothing than to do something, but gardeners often hope that a struggling plant eventually will turn the corner on its own. The thinking is that once the roots grow a bit more or the weather gets better, growth will take off.

While plants do their best to survive, the reality is that plants seldom overcome lousy soil and location issues to go on and suddenly thrive.

Plants that struggle beyond a first-season transition more often continue to struggle to hang on, or they go into a slow, gradual death slide.

So what is a better option?

Though it might seem radical, digging up the unhappy plant is usually the best long-term bet.

Sometimes just improving the soil and replanting in the same place is enough to make a big difference.

Other times, moving the plant to a more amenable location turns the table.

Most of the time, doing both works best.

This stunted 'Whipcord' arborvitae is being moved to a new location with improved soil.George Weigel

There is some risk to this. Yes, digging a struggling plant could be the finishing stress. But the downside of doing nothing is that the plant also could be on its way to horticultural Heaven anyway.

If it’s any consolation, veteran gardeners usually will tell you they’ve moved many a plant with surprisingly good results.

The trick is knowing how and when to make your move.

Try to dig as much of the existing rootball as possible, then have your new planting area dug and improved with compost to keep out-of-ground time to a minimum.

Use a tarp, burlap, or similar sturdy cloth under the rootball to keep clods of soil from falling off during transport, thereby tearing off roots along with them.

Lightly tamp the plant in place, add two to three inches of organic mulch, and soak well.

As for timing, avoid moving plants during hot, dry spells, and do it in early spring (before it gets too hot) or early fall (so roots have a chance to acclimate before the ground freezes). Next spring is best now.

It’s also best to move plants right before a rainy spell, during cloudy periods, or at least in the evening so moved plants will have a period of darkness to recover before facing the bright sun.

Digging and replanting can also solve other planting problems, such as this shrub that didn't have the burlap around its rootball removed before planting.George Weigel

Replanting in the same spot gives you a chance to correct planting miscues that might be behind the stunted growth. Common examples are planting too deeply, leaving the burlap on tree and shrub rootballs, and mulching excessively.

Sometimes moving plants just a few feet is enough to reverse a struggle, such as around a corner where a plant suddenly gets better light.

When competing tree roots are the issue, it’s usually not harmful to a healthy tree to remove up to 10 percent of its feeder roots and to replant your struggling plants into the cleared ground. However, keep in mind that the tree roots are going to grow back in – maybe even more vigorously if you’ve improved the soil. On the plus side, a few root-free years might be enough for a struggling plant to gain a competitive foothold.

Otherwise, look around the yard for more ideal settings to your struggling plant’s needs.

The bottom line is to not overlook the shovel as a solution to a stunted plant.

It’s one of the best weapons in your plant-fixing arsenal.

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