Five Reasons Your Trees Are Failing: A Bartlett Tree Expert Speaks Out

Trees are generally admired for their surface beauty, but their health and vigor springs from what’s underground. That’s according to Dr. Kelby Fite, Director of Research for Bartlett Tree Research Lab in Charlotte, North Carolina, who spoke to Maryland’s master gardeners last week. His lecture entitled ‘Managing the Landscape Below Ground’ provided a wealth of information about how to improve the life of the trees in our landscape. According to Fite, it all starts with the soil.

“We are all guilty of fouling up the soil,” he said. “But, it’s far easier to preserve soils than to remediate after they’re damaged.”

Before reaching for the fertilizer, Fite advises digging a little deeper into the source of the problem. Following are five common reasons that trees fail and what to do about them.

Soil Compaction

When it comes to tree health, nothing hurts a tree more than compacted soil. Often brought on by construction, soil compaction impacts trees at their roots, depriving them of essential water, oxygen and nutrients. It also makes it harder for a tree to anchor itself in the soil.

Compacted soil makes tree anchorage difficult 

Soil compaction occurs when soil particles are compressed by external factors like mechanical or human traffic, resulting in reduced pore volume (meaning there is less space for air and water.) Heavily compacted soils have a reduced rate of water infiltration and drainage and are often hydrophobic (meaning the water runs off). For a tree, this leads to poor growth, higher water needs and increased susceptibility to pests and disease.

Fertile, aerated soil

Compacted clay soil

Think of soil like a sponge, with large and small particles.

“What happens when we squeeze a sponge?” Fite asked. “We are increasing the amount of solid matter.”

It makes sense. Tree roots are extensive and with the exception of the taproot, located for the most part just 8 to 10 inches below the soil. They need space to grow. With compaction, however, many trees will never develop a taproot, instead establishing a network of weakened lateral roots that are unable to keep the tree vertical. And at the soil surface, the fine feeder roots (which under ideal conditions can extend 4 to 7 times the drip line of the tree) are compromised, too. This reduces a tree’s ability to absorb water, oxygen and nutrients and ultimately leads to its decline.

SOLUTION: Build away from a tree’s drip line and keep mowers and other machinery off the soil. For existing trees under stress, add a mulch circle. (More on that below.)

Raking up leaves deprives trees of important nutrients

This is a tough one. I’m not sure I’m ready to shred leaves and leave them all over my lawn. But think of it, we spend time and money to rake up one of our plants’ most important sources of nutrients, push them to the curb, then go to the store and buy them back again as mulch or soil additives.

“It’s not a great business model,” said Fite.

According to Fite, we are removing one pound of nitrogen per 1000 feet just by removing the leaves from our properties. This is a big loss for trees as well as other plants. And this doesn’t even take in to account the fossil fuels burned to operate leaf vacuums.

Our soils are low in organic matter because we are not allowing leaves to decompose like they do in the forest. When left alone, leaves return nitrogen and other organic matter to the soil. They also protect the soil surface, adding to its water holding capacity. And as they break down, they provide porosity and aeration, allowing more water to infiltrate the soil.

Shredded leaf mulch

SOLUTION: Shred your leaves with a mower and make leaf compost or leaf mold mulch (not the same thing.) For some great info on how to do both, click here for thespruce.com’s excellent article Rake leaves and make compost, mulch. 

Modified soils have higher pH which is bad for trees

In a perfect soil world, soils have a slightly acidic to neutral pH (a pH of 5.5 to 6.5). Urban and suburban soils, however, often contain debris left behind from construction. This generally results in a higher soil pH due to leeching from masonry walls and foundations.

Leeching from masonry leads to soils with higher pH

Trees growing in these locations may show signs of nutrient deficiency (like yellowing of leaves) and may be slower to establish. And irrigation water typically has higher pH, too. This means it gradually increases the pH of adjacent soils over time. This can result in a dramatic difference between the nutrient ability of your native soil and that affected by construction materials.

SOLUTION:  Do a soil test to determine the pH and get the turf out from under your trees. Lawn thrives on alkaline soil (that’s why we add lime.) But trees like a lower pH. All developed soils tend to have a higher pH and modified temperature, putting more heat stress on plants.

A soil test report from University of Delaware (my go-to destination for soil reports)

Lack of mulch

Mulch improves soil structure while providing protection to a tree’s roots. It supplies organic matter to the soil that reduces compaction. And it moderates soil temperatures, conserves moisture and eliminates competition from grass. Yet, many landscape trees are planted out in the lawn with no protection.

Fite recommends mulching out to the drip line of a tree if you can. It will help prevent ‘mower blight (or your mower banging into the trees) and also protect against stripping from string trimmers. Mowers, by the way, also contribute to soil compaction, especially when they’re operated in wet conditions.

Mowers contribute to soil compaction and can damage a tree

SOLUTION: Create a mulch circle around your trees. It will help protect them from mower damage and as the mulch decomposes, it will aerate the soil and provide nutrients.

Fertilizing when it won’t make any difference

According to Fite, fertilizer doesn’t fix everything. Pull a soil sample from around your tree first to determine whether or not to fertilize. Most soil labs will run diagnostics on your sample and send you back a prescription for what to add to your soil to improve its composition.

Before fertilizing, ask yourself what is the objective? If construction has occurred and interrupted a tree’s root zone, no amount of fertilizer is going to fix the problem.

And remember, although native soil usually contains lots of organic matter, during construction this layer is often buried under layers of sand or debris. Or sometimes, it’s stripped off entirely. No amount of fertilizer is going to bring life back to this kind of soil.

SOLUTION: Do a soil test to find out what your soil is made of before reaching for the fertilizer. Fix the soil first, then use fertilizer to adjust accordingly.

OTHER THINGS YOU CAN DO TO HELP YOUR TREES

Fite offered a couple additional suggestions for how to get your trees back in shape (assuming you haven’t destroyed most of the root system by building too close):

Invigorate the roots

Many times the best thing you can do for your trees is to invigorate their roots. Bartlett uses an air spade, a tool that uses an air compressor to generate a high velocity jet of air to dislodge the soil. The rush of air breaks up and ‘tills’ the soil without removing it to a depth of about 8’ (the depth of the feeder roots). This method of improving the soil leaves root systems intact.

Air spade in use at Western Illinois University

The air spade was originally developed by the military to clear land mines. Nowadays, it is used by landscapers and arborists to invigorate roots. After the soil is excavated, add soil, compost and mulch to settle the soil back down. Then water the tree.

Look into Biochar

Mulch breaks down because the microbes eat it for carbon, resulting in it having to be replaced every year. Charcoal, on the other hand, is stable, meaning it lasts for centuries. Biochar is a fine-grained, highly porous charcoal that is added to soil to help it retain water and nutrients. It acts like a dry sponge, but on its own contains no nutrients, so blend with compost for best results.

Biochar acts as a dry sponge, but contains no nutrients

“Put the two together and magic happens,” said Fite.

Buyer beware, though, biochar is not regulated, so buy from a reputable source and read the label carefully.

Kelby Fite, Ph.D. is a VP and Director at Bartlett Tree Research Lab.

Bees, Wasps and Hornets: Here’s How To Tell The Difference

Four common bees and wasps

What is the difference between bees, wasps and hornets? This is a question I tend to ask myself, especially when surrounded by swarms of hungry yellow jackets while dining outside. I, for one, know from experience that fuzzy honeybees can make excellent garden companions. But, what’s up with their skinny yellow and black striped brethren? Do they have any value? They seem interested only in stinging me. Continue reading

Help Save The Monarchs With These 4 Great Milkweeds

Monarch butterfly on swamp milkweed

Last week, I was manning the booth at the Montgomery County Fairgrounds Demonstration Garden (yes, it’s a mouthful), when someone plopped a tall, spindly plant down onto the table. The plant looked pretty pitiful; the flowers were long gone and the paddle-shaped leaves had circular holes in them. But upon closer examination of the stems, I spotted a string of tiny, lantern-shaped pupae along with a company of black, yellow and white striped caterpillars. The plant was none other than milkweed and the chrysalises contained baby monarchs in the process of forming.

We placed the milkweed next to a grouping of Joe-Pye weed and sat back to see what would happen.

Things aren’t looking up for the monarch butterfly

Monarch butterflies are considered by many to be the ‘king’ of butterflies, with a wing-span of over 4 inches (hence the name, monarch.) But, according to the National Wildlife Federation, their population in North America is in steep decline. Over the past twenty years, monarch numbers have plummeted by an astonishing 90 percent, leading scientists to question what’s happening. They suspect the answer is tied up with milkweed.

Close-up of swamp milkweed, Asclepias incarnata

Why milkweed you might ask? Because milkweed is the host plant for monarchs, and monarch caterpillars will only eat plants in the family. But milkweed has been disappearing, too. Over the last couple decades, large-scale clearing of meadows and prairies for development coupled with heavy pesticide use has resulted in the plants becoming increasingly scarce, placing in jeopardy the tiny population that depends on it for survival.

The problem is so big that according to one National Public Radio (npr) report, monarch populations overwintering in Mexico that averaged around nine hectares from 1995 to 2002, in 2014 took up less than one.*

A migratory insect

Every spring, thousands of Eastern monarchs begin their annual migration across the Great Plains on their journey from Mexico to Canada, covering over 3,000 miles in the process. And every fall, they do the trip in reverse. The insects breed along the way, stopping three times to go through four stages of development: egg, larvae (caterpillar), chrysalis and adult butterfly. The new butterflies live for just four to eight weeks, long enough to fly further north and lay their eggs. Then the next butterfly continues the journey.

Millions of monarch butterflies flying in Mexico

This means that it takes three butterflies to make it all the way to Canada.

Incredibly, the fourth generation butterfly born in Canada lives a bit longer. This is the monarch that migrates back to warmer climates like Mexico. This butterfly lives for six to eight months, long enough for it to start the whole process over again in the spring. (To read more about the monarch butterfly cycle, click here.

A misunderstood plant

The milkweed family, Asclepias, is composed of more than 100 varieties of leafy plants. Tall and upright with long, elliptical-shaped leaves, milkweeds bear dense clusters of vanilla-scented rosy-pink or orange flowers. The plant owes its common name to the milky latex that oozes when a stem is snapped.

Milkweed provides all the nourishment the four generations of monarchs need to transform from larvae into butterflies. The baby caterpillars feed on the leaves until fully grown, and then attach themselves to a stem or leaf to start the process of metamorphosis. Once they hatch, the monarchs move on to other flowers to live out their short life.

Monarch chrysalis hanging from a milkweed stem

In addition to nourishment, milkweed provides other advantages to monarchs. As the caterpillars undergo transformation in chrysalis, they ingest toxic chemicals secreted in the plants’ sticky sap. These chemicals, called cardenolides, provide the caterpillars with a key defense against would-be predators such as birds and mice.

Monarch caterpillar munching on milkweed

Specifically, cardenolides are so toxic and bitter tasting to other vertebrate species that they have learned to associate bad taste with the butterflies’ distinctive orange and black markings. Although as adults, monarchs no longer eat milkweed, they are able to sequester the toxins that they ingested as larvae, providing them with protection against many predators during the remainder of their lifespan.

Monarchs’ distinctive colors help ward of predators

Monarch butterflies only lay one egg per leaf, but they lay eggs on lots of leaves and always on more than one plant. They are mini eating machines. Three days after it arrived to the fair, the caterpillars had devoured the plant they rode in on; in their place hung rows of tiny pupae.

Many of us are familiar with the roadside milkweed, but lesser known is that there are now many beautiful perennial varieties that can enhance your garden while helping you do your part to save the monarch species.

Common milkweed, Asclepias syriaca

Ready to save the monarchs? Here are some great new milkweed varieties to try, available at many local nurseries.

Butterfly Weed, Asclepias tuberosa

This bright orange beauty blooms from May to September. It just won Perennial of the Year for its brilliant flowers, hardy, upright stems and good drought-tolerance.

Butterfly weed, Asclepias tuberosa

Or, for a great yellow variety, try ‘Hello Yellow’, available through White Flower Farm.

Asclepias tuberosa ‘Hello Yellow’

 

Swamp Milkweed, Asclepias incarnata

Swamp milkweed ‘Cinderella’ available at Perennials.com

Or try a mix of hot colors, Asclepias Gay Butterflies Mixture, available at White Flower Farm.

Asclepias Gay Butterflies Mixture

Milkweed generally blooms from June to August. All varieties need full sun and well-drained soil. If you observe caterpillars or chrysalises on your plant, wait until the butterflies have flown away, then simply cut the plant to the ground.

* Monarch populations are measured in hectares, which roughly equal 2 1/2 acres.

 

Pass The Vinegar, I Need To Water My Plants

After 14 days without water, only the plants treated with vinegar survived. NIKEN

Before you wrinkle your nose at this, hear me out, because it’s true. Scientists in Japan have discovered that ‘watering’ plants with vinegar can help them survive longer in drought conditions. I don’t know about you, but I’m reaching for that bottle of white vinegar right now to see if my hydrangeas wouldn’t like a swig.

Last week, scientists at the RIKEN Center for Sustainable Resource Science (CSRS) published the results of a study in Nature Plants that reported they had uncovered a novel way to help plants survive drought. The study revealed that the researchers had stumbled upon a new biological pathway in plants that sprang into action in times of water stress. By further unraveling the pathway and the roles different chemicals played within it, the scientists discovered they could induce greater drought tolerance by growing plants in vinegar.

We all know vinegar’s miraculous properties for cleaning windows and removing stains from carpets, but helping plants cope with drought? Now that is shocking news indeed.

My hydrangea showing signs of water stress 

 

The study began with a collaborative effort to understand the plant Arabidopsis, also known as thale cress. A relative of cabbage and mustard, the genus of small flowering plants is the first plant to have its entire genome sequenced (which makes it one of the model organisms used for studying plant biology.)  Most importantly for the purposes of the study, Arabidopsis has a strong drought tolerance. This is due to a mutation to an enzyme called HDA6 (histone desacetylase6) that allows the plant to grow normally without water for extended periods of time.

Microscopic view of anther of Arabidopsis, also known as thale cress

Initial testing showed that when experiencing drought stress, Arabidopsis uses HDA6 to activate a biological pathway that produces acetate, the main component of vinegar. The HDA6 enzyme acts as a switch, controlling which type of metabolic pathway (sequence of chemical reactions undergone by a compound in a living organism) is active. While normal plants are busy using metabolic pathways to break down sugar for energy, in times of drought, the Arabidopsis plants switch to the acetate-producing pathway.

To find out how this switch works in times of water stress, scientists conducted an experiment. They grew normal plants under drought conditions, treating some with water, some with organic acids and others with acetic acid. After 14 days, 70% of the plants treated with acetic acid were still living while all of the other plants had died.

Microscopic view of stem epidermis of thale cress showing hairs and stomata

By measuring the amounts of acetate in Arabidopsis under stress, the team discovered that there was a direct correlation between the amount of acetate produced during periods of drought and how well the plants survived. And even more exciting, the team carried out the same experiment on rice, wheat and maize and found that their drought tolerance increased as well when grown in optimal acetic acid concentrations.

Close-up of rice plant

The implications of this research are huge. In an increasingly water-stressed future, this discovery might offer a simple, low-cost alternative to genetic engineering. I’m not sure if it will help my hydrangeas battle another scorching Maryland summer, but I’ll let you know.

 

 

Shooting The Breeze With The Head Of Versailles’ Kitchen Garden

Antoine Jacobsohn, Head of the King’s Kitchen Garden at Versailles

What if you could walk down the street and, next to the shrubs and other flowers, fruits and vegetables were growing? That’s the hope of Antoine Jacobsohn, Head of the King’s Kitchen Garden at the Palace of Versailles. I spent an afternoon with Jacobsohn recently when he came to DC’s Alliance Française to speak about his role in managing this famous French garden. Continue reading

Trade In Your Lawn For A Low-Maintenance Meadow Garden

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A suburban meadow can help free you from tiresome yard work

These days, many of us are searching for alternatives to conventional lawn and garden care, a chore that has become increasingly dependent on time and maintenance as well as pesticides and other poisons. The suburban meadow offers a beautiful solution to this problem. Continue reading

5 Ways You Can Honor Our Planet on Earth Day

earth1

It’s been a while now since Earth Day first made its debut on April 22, 1970. I vaguely remember the strangeness of being let out of school early to pick up trash in the nearby woods. The idea seemed entirely foreign to us at the time, which means, of course, that we were used to throwing our garbage on the ground. Hard to imagine in this day and age that was the common mindset. Continue reading

Now There’s Proof: Bees Make Bigger Plants

Bumblebee pollinating mustard plant/ Photo: University of Zurich (UZH)

There’s been a lot of buzz in recent years about pollinators, especially of the fuzzy yellow and black kind. Now comes news that bumblebees not only help plants propagate, but they also have a positive effect on their size, fragrance and color. It’s all part of a new experiment by researchers at the University of Zurich that proves bees do it bigger and better. Continue reading

Is the Self-Healing House the Garden of the Future?

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Image via Edwin Indira Waskita

There’s a fascinating image that has stuck with me ever since, years ago, I read the sci-fi novel Goodbye and Thanks For All the Fish (the fourth installation in the series the Hitchhiker’s Guide to the Galaxy.) In the novel, author Douglas Adams describes a four-walled house turned inside out. If you entered the house, you found yourself ‘outside’ in a green space, complete with lawn, benches and walking paths. If you exited the house, you found yourself ‘inside’ in a far less desirable place Adams termed the Asylum. Continue reading

Bee ID: How To Make Sense Of The Buzz In Your Garden

cover.bumble bee

Aren’t they cute?

One of the many things I love about gardening is working in tandem with my many fuzzy, buzzing friends. Dutifully arriving on the job each morning, they hover beside me, yielding as one mass each time I shift position in the garden. Sometimes, I’ve been brave (or stupid) enough to touch one of the downy creatures, and they’ve agreed to let me stroke them. Feeling the tiny vibrations of all that industrious activity never ceases to amaze me. Continue reading