Garden Plot: How to handle destructive willow oaks

Mike returns to Chantilly!

Mike will appear on Saturday, Feb. 22 and Sunday, Feb. 23 at the long-running Capital Remodel and Garden Show at the Dulles Expo Center in Chantilly. Exact times and details soon, but expect to hear about tomatoes, organic lawn care, compost—and, of course—answers to your toughest garden questions! (Or evasion of said questions, which is more fun…)

See the Philly Flower Show like a pro —at a great price!

Long-time listeners know that I am ga-ga over the Philadelphia Flower Show — the oldest and largest (and best!) indoor flower show in the world. This year, the show will take us on a Riviera Holiday from Feb. 28 (members’ preview) through March 8.

If you’re ready to commit now, you can save serious money on the show’s website, the only place to get these deals.

All Pennsylvania Horticultural Society memberships are discounted online and include flower show tickets plus bonuses.

The most amazing deal is a “Friends and Family” membership for the discounted price of $135.

You become a member of PHS for a year and receive four adult tickets and two children’s tickets, which would cost you over $200 at the door.

Plus, you get discounts at the show, reciprocal membership at 300 botanic gardens, access to the Member’s Lounge at the show (a place to sit down!), a subscription to the PHS magazine, GROW (produced by two of my former colleagues from ORGANIC GARDENING magazine), and more.

But you must commit by Feb 3.

I’m committable Mike McGrath, urging you to check out all your Philly Flower Show options.

The roots of a willow oak

Reed in Vienna, Virginia, writes: “Roots from my large willow oak tree are starting to break up my asphalt driveway.  What should I do or not do to correct this problem?”

We’ll begin to answer that question below, Reed. For now, let us praise this tree!

A true oak tree in the red oak family, the willow oak proves its oaken identity by producing many acorns every year.

The “willow” part comes from its unique leaves, which closely resemble those of willows, much more so than other oak trees.

Like willows, it is also a water lover. It’s found naturally near river bottoms and other sources of water. It grows in sun or shade, making it an exceptional landscape tree.

But it grows so tall so quickly that it’s often taken down, which is truly unfortunate, as it has become endangered in Pennsylvania and New Jersey.

Getting to the root of the problem

Again, Reed asked: “Roots from my large willow oak tree are starting to break up my asphalt driveway.  What should I do or not do to correct this problem?”

Tough call, Reed. Willow oaks are exceptional trees, but they grow really large really fast and their roots are known to break up driveways and sidewalks.

Can the driveway possibly be re-configured to accommodate the roots? (Those roots are a sign of a happy, healthy tree.)

If not, contact an arborist, who would use a device called an “air spade” to uncover the underground roots and then sever the ones encroaching on the driveway, seal the cuts with white latex paint and install a rhizome barrier to try and divert new roots.

Wait until the tree has time to heal and then have the driveway repaired.

Tree root treatise

Let’s discuss aboveground tree roots in general.

If you’re planting a new tree near a structure, driveway or pavement, choose one with roots that are well behaved. Your local state (or D.C.) extension service will have a list.

If you have an existing tree flexing its underground muscles, try and accommodate it if possible, as aboveground roots are the sign of a healthy tree.

Otherwise, contact an arborist and have them use an “air spade” to uncover the roots and then sever the ones that are encroaching, seal the cuts with white latex paint and install the rhizome barrier to try and divert new roots.

And DO call a pro! This is NOT a do-it-yourself project!

If the roots are in a lawn, add just enough soil or compost to cover the roots and make mowing easier. This won’t hurt the tree, but any mulch or soil touching the trunk will cause an early demise.

NO VOLCANO MULCHING! If your landscaper insists on doing it, hoe the mulch away and find another landscaper.

Seed catalog of the day

The new catalog from Breck’s — in business since 1818 — has a great offer of 50 to 75% off virtually all perennials without coupons or codes.

How about an oriental poppy named ‘Heartbeat’ that’s weather-resistant with an extended bloom time?

A six-plant mixture of colorful Siberian “peacock butterfly” Iris?

Or “Strawberry and Cream” — a uniquely colored coneflower that pollinators are said to love?

I personally love the look of “Pink Hawaiian Coral” peony, an APS gold medal winner that, unlike my peonies, requires no staking!

Or old-fashioned bleeding hearts — one of the oldest plants still in cultivation and a perennial garden favorite.

Or consider king-sized hellebores — perhaps the most deer-resistant flowering plant of all.

Request a catalog or see it all on Breck’s website.

Mike McGrath was Editor-in-Chief of ORGANIC GARDENING magazine from 1990 through 1997. He has been the host of the nationally syndicated Public Radio show “You Bet Your Garden” since 1998 and Garden Editor for WTOP since 1999. Send him your garden or pest control questions at

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