#019 - Getting to the Root of the Problem

Field Notes from a Plant Detective

Ever since people realized that I know a bit about plants, I’ve been the recipient of text messages, phone calls, and Instagram DMs from friends and acquaintances asking me to diagnose their plant problems. Why is my tree dropping branches? Why are these leaves scorched at the edges? Am I watering too much, or not enough? Is my plant happy? These questions come up constantly, and they rarely have simple answers. The next few Hot Plant Tips will take a closer look at the things that can go wrong with plants, whether they are indoors or out. This article will focus on outdoor plant problems, the next will cover indoor plant care and, after that, we’ll head into the slightly grody world of plant pests and diseases.

Before diving into plant problem diagnosis and becoming a plant detective, the first principle to keep in mind is that plants should be observed where they grow. You cannot make a proper diagnosis from a single leaf, a twig, or a blurry iPhone photo someone shows you. To understand what is going on, you need to look at the whole plant, check the soil, and study the sun and shade conditions. More often than not, the root of the problem is not a pest or disease but a human misstep. Poor soil preparation, inconsistent watering, bad planting practices, or nutrient deficiencies are the usual culprits. Unfortunately, it is common for people to overlook these possibilities and jump straight to pesticides or fertilizers, which rarely helps and often makes matters worse.

Watering and Drainage Problems

Water is usually the best place to start when having a conversation about plant health. Too little, and you have drought stress, too much, and you suffocate roots, and both can kill a plant. Newly planted trees and shrubs are especially vulnerable since their root systems are small and constrained from months or years in containers. They need steady, deep watering to push roots outward into the surrounding soil. Quick sprays from a hose or short, daily irrigation cycles are two of the worst things you can do for new plants. You will only encourage shallow roots and leave plants dependent on daily irrigation. The goal should always be to water deeply enough that the soil is moist well beyond the original rootball (deep and wide), which encourages a plant to build a strong and extensive root system.

One of the trickiest things about watering is that overwatering and underwatering look surprisingly similar. A plant that is too dry will wilt, curl its leaves, scorch at the edges, or even drop branches. A plant that is drowning in water will often display the exact same signs. The difference is that in saturated soil, roots are literally suffocating. Deprived of oxygen, they rot and lose the ability to absorb nutrients. This condition is known as chlorosis, where leaves turn pale yellow or even white due to insufficient chlorophyll.

Drainage plays a huge role in plant health. Much of Southern California sits on heavy clay soils with poor percolation. In compacted or rocky sites, a plant pit can hold water like a tub for days. A simple test is to dig the hole and fill it with water before planting. If it is still full a few hours later, your site has very poor drainage. Your best option at that point is to select plants that naturally tolerate saturated conditions. The Theodore Payne Foundation has a useful list of native species that can survive those kinds of settings.

Another water-related problem comes from salt buildup. In cold climates, salt damage usually results from winter road salt washing into planting areas. In Southern California, the source is more often recycled irrigation water compounded by excessive fertilization. Typical reclaimed water treatment does not remove mineral salts like sodium, boron, or chloride. Over time these salts accumulate in the soil, leaving a white crust on soil surfaces, burning leaf tips, and stunting growth. Sometimes foliage even turns chlorotic from the stress, which people often mistake for drought. The best solution is called leaching, which is applying additional water periodically to flush salts down below the root zone. Potable water is best for this, but recycled water can work when its salt concentration is seasonally low. On a project in Redwood City, we had soils on site that were very heavy clay, and the reclaimed water supply carried particularly high levels of salts. The only way forward was to select a plant palette that could tolerate both the slow-draining conditions and the salt load, which required careful research and trial to find species resilient enough to survive.

Planting Depth and Root Issues

Water is not the only source of problems. Mistakes often begin at the very moment of planting. A plant pit that is too shallow constrains roots, while a hole that is too deep can drown a tree. The guideline is simple: dig twice as wide as the rootball and no deeper. Trees should sit on compacted native soil so that the trunk flare ends up at grade. If you dig too deep and replace the soil under the tree with loose planting soil, the weight of the tree will compact it over time, causing the trunk flare to sink below grade, setting the stage for rot and decline. Another key step is to scarify or roughen the sides of the planting pit so that roots do not hit a smooth, impenetrable wall of soil. Without this step, roots often refuse to leave the pit and will never expand outward. And while it may be tempting to enrich the hole with rich compost and amendments, it is a mistake to do so without blending it with the surrounding soil. Roots will happily circle in the pocket of good soil and refuse to establish beyond it.

Root girdling is another problem that starts during planting. Girdling occurs when circling roots tighten around the trunk, slowly strangling the tree. It usually starts in the nursery when trees sit in their containers too long and become rootbound. If these circling roots are not corrected at planting, they will keep pressing against the trunk as both expand, eventually cutting off the tree from its roots. I used to see this problem quite frequently when I first started visiting nurseries, but practices have improved considerably in the past twenty years, and girdling is less common today than in decades past, though it still appears often enough to warrant caution.

Physical Damage

Even perfectly planted trees are vulnerable to mechanical injury. Lawn mowers and string trimmers are some of the worst offenders. Bark and cambium wounds may look minor at first but they never fully heal and that area of the tree will always remain weak. The simplest protection is to keep a mulch ring two to three feet around the trunk and keep lawn equipment far away.

Staking injuries are another common problem. Ties that are too tight or left on for too long will cut into bark, killing tissue and blocking nutrient flow. A young tree should not be tied like its life depends on it. Stakes are there to help it through the first year or two, not to be a permanent fixture. Check them regularly, loosen ties as needed, and remove them once the tree is stable. Always use wide, flexible ties that cannot bite into bark. We always include a specific detail just for tree staking.

Tree structure also matters. Narrow crotch angles, the tight V-shaped unions between branches or between a branch and the trunk, are structurally weak and should be avoided during tree selection. The term itself, ‘narrow crotch angle,’ always sounds a little funny when you first say it out loud, but the consequences are serious. These unions trap bark between stems instead of allowing strong wood connections to form. Over time, pressure from growth and weight can cause catastrophic splits. Trees with wider U-shaped crotches form much stronger unions, and that should be a factor when selecting trees. A friend of mine recently sent me a photo of her father’s beloved pear tree that had split right down the middle and collapsed to the ground. It turned out to be a classic case of a narrow crotch angle. The branches had grown in such a tight V that bark was trapped between them rather than wood fibers fusing properly. With the weight of fruit and the pressure of growth, the tree tore itself apart. It’s a dramatic but very real example of why branch structure matters and a good reminder that certain species are especially prone to this problem.

Troubleshooting Symptoms

When diagnosing a plant that looks stressed, the best strategy is to look for patterns in the landscape. If multiple species across a site are failing in the same way, it is usually a systemic problem like irrigation or soil conditions. An incorrectly programmed or broken irrigation valve can wipe out a whole section of a project, whether it’s via over- or under-watering. On the other hand, if only one tree is suffering while others nearby are thriving, the issue is more likely local: an improper planting depth, a girdling root, or trunk damage from maintenance equipment.

So be a plant detective. The challenge and the fun of this work is putting the pieces together. Plant decline is rarely mysterious once you know what to look for, but it does require a full investigation of the site, the soil, and the planting history. The process is less about spotting a single leaf symptom and more about following the trail of evidence.

By paying close attention to water management, soil preparation, planting depth, and physical site conditions, you can prevent many of the most common causes of outdoor plant decline. As landscape architects, we may feel separated from our projects and plants while we sit behind our computer screens, but knowing the major causes of plant failure is important. Good plant installation and care shapes whether a landscape survives its first few years or fails before it ever has the chance to mature. With good installation practices and thoughtful observation afterward, plants are far more likely to establish strong roots and continue growing for the long term, and it is our responsibility to identify any possible issues we may see with the spaces we design.