Volcano Mulching

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We’re starting to see volcanoes!

It seems to be a yearly occurrence in many front yards. I’m talking about volcano mulching – piling large mounds of mulch around the trunks of trees and shrubs – a practice that slowly kills the very plants it was intended to help. It’s TOO MUCH of a good thing!

“Don’t think that volcano mulching is OK because everyone is doing it,” says Temple University Horticulture and Landscape Architecture Professor, Eva Monheim. “Just because something is done doesn’t make it right. It causes bark to rot and roots get smothered. You have an unstable tree.”

Volcano mulching is too much of a good thing.

Volcano mulching is too much of a good thing.

Mulch is used to cover soil around plantings for a number of reasons: It assists in reducing evaporation; it stops sunlight from hitting the soil so fewer weed seeds germinate; as the mulch decomposes, it breaks down and provides organic matter to the soil; and, mulch rings around trees can keep lawnmowers and string trimmers at a distance. Mulch is aesthetically pleasing and can probably be compared to the frosting on a cake.

So, what’s the problem?

The bark of a tree is its outermost protective layer. It needs to be exposed to the air in order to function properly. Moisture retained by the mulch softens the bark; as mulch decomposes it also decomposes the trunk of the tree – making it susceptible to fungus and insects.

Corey Cummings, Past President of the Maine Arborist Association, adds, “thick mulch provides great habitat for insects and rodents to crawl around in, most of the time undetected. We know what rodents can do to the base of trees in the winter. With the forest under a barage of attacks by native and invasive pests we don’t need to do anything that would lessen the vigor of a tree to help fight off pests. If done properly mulching can benefit the tree’s health and improve its habitat”

“Mulch cuts off the supply of oxygen to the roots, essentially suffocating them” says Mark Fuance, a Maine Certified Nursery and Landscape Professional (MCN/MCL). “It has the same effect as planting a tree too deeply – another reason for premature decline.”

After years of volcano mulching this tree is now in decline.

After years of volcano mulching this tree is now in decline.

So, what’s a homeowner to do?

How to make a tree mulch ring:

Prepare: Carefully remove grass and weeds from around the trunk. Do not simply pile mulch on top of existing grass and weeds in an attempt to smother them. You will also inadvertently smother the roots of your tree.

Size: A two to three foot radius of mulch around a tree will allow for plenty of space to keep damaging equipment away from a tree’s bark.

Depth: Two to three inches of mulch will keep most weed seeds from germinating in the soil beneath but will still allow water and air to penetrate. Mark Fuance, MCN/MCL, says, “At the base of every tree is the root flare or crown.  This flare should always be two inches or so above the soil or mulch surface.  That will allow sufficient air to reach the roots.” If yearly mulching is done, be aware that in time it can result in too much thickness. In this case, “Old mulch should be removed before installing new material,” according to Mark Fuance. “Landscapers need to take the time to expose the root flare.”

Material: My first choice is dark-colored bark mulch. Well-aged wood chips and compost are fine. I don’t recommend dyed mulches or chopped rubber mulch. There’s concern about chemical residue leaching into the soil. Fresh wood chips and sawdust should not be used because they can deplete the nitrogen in the soil as they decompose causing chlorosis (yellowing leaves).

Mature trees can be harmed by too much mulch.

Mature trees can be harmed by too much mulch.

Know The Facts: Large, well-established trees do not need to be mulched. If you feel compelled to mulch to match surrounding beds follow the steps above.

Well-intentioned people who don’t know what’s really happening to their trees often build the mulch volcanoes. Uninformed “landscapers” think it’s ok. It’s simply a lack of knowledge about proper horticultural practices.

Now you know better! Protect your trees.

Volcano mulchingproper mulching





Lisa Colburn is a Master Gardener in Penobscot County, Maine and Sarasota County, Florida.
She is the author of The Maine Garden Journal – Insider secrets from Maine people who love to put their hands in the dirt.
Contact Lisa at (207) 404-3494 or by email:

Garden Surprises and Successes

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At this time of year, when my outdoor gardening starts winding down, I take the time to look at photos I’ve taken throughout the year. It’s time to acknowledge some of the surprises and successes. It’s time to give thanks and be grateful that I am a gardener – there’s really no better pursuit where one can create beauty and cultivate food for the body and the soul.

One of the gadgets I got this year was a rain chain. I’d been lusting after one for a number of years. Consider rain chains functional garden art – beautiful to look at, mesmerizing to listen to and a fascinating downspout you’ll want to place in a prominent location. The rain chain came from Rain Chains Direct.


One of my biggest surprises this year has been the Albion day-neutral strawberries planted last spring. I planted them in raised beds and kept lightweight row cover on them all summer – to protect them from insect pests. They were mulched with straw so developing berries were never sitting on bare soil. I’ve been picking strawberries since the end of July. I added another layer of row cover for additional protection from frost at the end of October. I picked my last berries in November!

Albion Day-neutral Strawberries

I’ve had a fabulous year in the greenhouse where I grow tomatoes – planted directly in the ground. I grow several kinds of tomatoes. I’m particularly fond of the big Beefsteaks for sauces and sandwiches but the workhorse of my greenhouse is definitely the grape tomato. By the end of the season, they have climbed all over the greenhouse dripping clusters of tomatoes as they grow. Visitors are always amazed at the lavish display. My favorite is Red Pearl available from Johnny’s Seeds. They’re nearly seedless so perfect for dehydrating.

'Red Pearl' grape tomato from Johnny's Seeds

I’ve mentioned it before and I’ll mention it again because I just have to rave about the abundant, show-stopping blooms of GauraRosy Jane’. I had just one plant, located on the edge of a paved driveway in full sun – a tough location – hot and dry. Now, even with frost and cold winds, it’s still looking great. The long flower stems always seem to be swaying in the wind like whirling butterflies, one of its common names. It’s shown in this photo with Verbena bonariensis, Japanese forest grass and a dark-leafed canna. Wow!

I've mentioned it before and I'll mention it again because I just have to rave about the abundant, show-stopping blooms of Rosy Jane gaura. I had just one plant, located on the edge of a paved driveway in full sun - a tough location - hot and dry. Now, even with frost and cold winds, it's still looking great. The long flower stems always seem to be swaying in the wind like whirling butterflies, one of its common names. It's shown in this photo with Verbena bonariensis, Japanese forest grass and a dark-leafed canna. Wow!

Every year I plant sunflowers. I’ve been particularly fond of the standard big, golden yellow ones, but this year I planted a packet of mixed sunflower seeds. I was surprised to find a few new favorites. The rich color of this sunflower has inspired me to start painting again.

Zone 3-4 Image 4

This must be the year that I take a crack at flowers in new colors. At first, I was taken aback by the color of Queen Red Lime zinnia but the more I used it in floral arrangement, the more I loved how it complemented dark-colored flowers particularly burgundy. It’s now a must-have zinnia on my list for next year.

'Queen Red Lime' Zinnia

Filler, Spiller and Thriller!


I love placing containers throughout my gardens. I’m particularly fond of large, glazed clay pots. They elevate plants up to eye-level where they can be best appreciated. Soil in pottery containers warms up faster than the surrounding garden – great for large-leafed tropical plants that also benefit from the reduced root competition. Tropical plants are heavy feeders and welcome reliable moisture. I water almost daily with a weak solution of high nitrogen fertilizer.

I typically follow the container planting guidelines that suggest you have a filler, a spiller and a thriller.

Canna 'Pretoria', Scaevola 'Topaz Pink', and Euphorbia 'Diamond Frost'

In this container my thriller is Canna ‘Pretoria’, and a combination of two plants acts as both a spiller and a filler. Euphorbia ‘Diamond Frost’ and Scaevola ‘Topaz Pink’ grow through each other and create a fabulous contrast with this deep burgundy pot.


Alocasia 'Calidora', Coleus 'Redhead'. Coleus 'Smallwood Driveway, begonia and pale blue lobelia

I always plant a few containers with elephant ear plants.  This glazed pickle crock greets people as they come to my front door. (Note: make sure to drill a few holes in the bottom of pots for drainage.) The thriller is a large, impressive elephant ear plant. The fillers are two kinds of coleus and a begonia. A delicate pale blue lobelia is the spiller. As you can imagine, this container, packed with plants, requires lots of attention to continue looking its best. I water it almost every day.


My end-of-June garden


My garden was featured in a garden tour at the end of June. While June can be a fabulous month for garden tours in most of the country, my garden is usually at its best in July. I think my garden looked better the week after the garden tour! and, two weeks later, it’s even prettier.

While I’m weeding my gardens, I pay special attention to volunteers that have popped up throughout my ornamental and vegetable gardens. I’m particularly fond of this Dianthus that’s been appearing throughout my gardens.

Dainthus sp.

Dianthus always seems to find the right place to volunteer – this time near a small water feature.

One of the delights of having a garden is being able to eat fresh salad greens all summer long. Right now, my spinach and lettuce are at their best.

Heirloom Bloomsdale Longstanding Spinach and Black-seeded Simson lettuce

Heirloom Bloomsdale Longstanding Spinach and Black-seeded Simpson lettuce

Heirloom Bloomsdale Longstanding Spinach has a fabulous yield and is slow to bolt. I’ve been plucking small leaves to put in salads and we’ve been enjoying it with dinner – steamed with a dab of butter.


One of the secrets to using fewer pesticides on my food crops is using floating row cover to keep the insects away from the plants.

Floating Row Cover

Floating Row Cover keeps the insects away so I don’t have to spray.

In these photos you see my broccoli and kale under cover. The kale leaves are always perfect and my broccoli is beautiful!


I’m loving being outside to experience my garden in bloom. My oriental poppies stunned everyone with their size and color this year.

Oriental Poppies

Oriental Poppies

Because we had a cool spring, they bloomed later than usual. The last ones to bloom are extending the show. They were definitely one of my WOW plants!


My garden shed has been flanked by a few large-leafed, moisture-loving plants for years. This year, they’ve grown so large that we’re having a hard time getting into the shed.

Astilboides tabularis on the left and Duck's Foot Rodgersia on the right.

Astilboides tabularis on the left and Duck’s Foot Rodgersia on the right.

On the left is Astilboides tabularis and on the right is Duck’s Foot Rodgersia (Rodgersia podophylla). For the time being, we’re squeezing through the foliage, looking for dinosaurs.


I love to have a touch of whimsy in the garden. This year, I took advantage of a tree trunk that houses a chickadee family.

Tree lady

Tree Lady

Tree lady protects her flock.

Snowbird Gardener Inspiration – Vacation to Sunny Florida!


What does a snowbound northerner crave after a brutal winter? GARDENS!

I’ve had the good fortune to be able to visit the fabulous Marie Selby Botanical Gardens in Sarasota, Florida during spring break for several winters. Many of the tropical plants grown at this garden inspire my gardens in Maine in the summer time. Here are a few of the plants that got my attention this year.


Caladiums – Who needs flowers with leaves like this? I’ve had good luck growing them in Maine as long as I give them a head start in the house. They detest cold soils and may fail to sprout if planted directly in the ground in spring.


Staghorn Ferns make fabulous houseplants. Several of my friends grow them in Maine.


I’ve grown plenty of Alocasia in my garden in the summer but I’ll be looking for this very different one. I love the white markings. Envy!! I start these in a warm area in the house to give them a head start.

Tropical pitcher plants

Tropical pitcher plants will become a conversation piece houseplant.
(Nepenthes sp.)

Tropical pitcher plants

Tropical pitcher plants love the warm greenhouse at the Marie Selby Botanical Garden.

Tropical pitcher plants

Tropical pitcher plants.

Australian Tree Fern

I have a love affair with fern leaves. This Australian Tree Fern towered over me – beautiful, lacy, sculptural leaves. I’ve got to try it as a houseplant.


The Marie Selby Botanical Garden is know for its world-class orchid collection.


This tropical orchid is related to the beautiful lady slippers that grow in northern areas.

For more information about growing these beautiful tropical plants go to the Marie Selby Botanical Garden website: http://www.selby.org/

I highly recommend a vacation to a warmer area – for gardening inspiration and to recharge your creative energy. When I return to Maine, I’ll be ready to put my hands in the dirt and start my gardening. My suitcase will certainly have room for a few “green travelers” from Florida! (An Australian Tree Fern, perhaps?)

The Benefit of Snow – YOU CAN GROW THAT!

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It’s been a particularly snowy winter in Maine. Skiers and snowmobilers have been ecstatic with the accumulation of the white stuff… but gardeners only measure how much snow has to melt before we see the ground.

On the positive side:
Snow can make a plain little table into a piece of art!


Birds like snow art too!


Snow insulates the soil, buffers the extremes in temperature and protects all my dormant plants.

Snow gives you a different perspective on your garden.


I’ll have to be content to look outside through these windows…


..with my houseplants, patiently awaiting Spring.

October in a Maine Garden


There’s still lots of color to be found in my Orono, Maine garden.

Hydrangea 'Strawberry Vanilla'

Hydrangea ‘Strawberry Vanilla’ – Pure white in summer and brilliant pink by fall.

Castor Bean Pods

Beautiful castor bean pods (Ricinus communis) command attention but beware, they’re poisonous


Spirea japonica ‘Firelight’ displays a remarkable mixture of pink, gold, orange and red.

Rudbeckia hirta 'Indian Summer'

Rudbeckia hirta ‘Indian Summer’ blooms and blooms and …

Verbena bonariensis

Verbena bonariensis volunteers throughout my garden