Growing Concerns 589: Ash tree replacements, rare seeds

I:n this issue:

Two replacements for ash trees in emerald ash borer areas
     Update 2014 and a complete 28-tree list
In search of rare seeds
Mulch and bugs, AOK to let it be!
Thumbs up and down to fall rain and tending new trees

Katsura and dawn redwood: Good replacements for ash trees


Dear Janet,

Japanese katsura (Cercidiphyllum japonicum) should be on your list of replacements for ash trees, as another excellent tree. It's upright, has a nice shape and butter-yellow leaves that all drop at one time in fall.

As for dawn redwood (Metasequoia glyptostroboides) that's on your list, it's beautiful but it requires a lot of space. One should allow at least a fifteen foot square area. This is a tree you would not want to limb up as you lose the beauty of the structure. This actually is not a shade tree but a beautiful specimen that gets very broad at the bottom. It has soft, sweet-smelling needles and apricot fall color. Since it loses its needles in fall it looks dead in the winter which is not a good look for some people. I did not provide enough room and recently had to take mine out, which broke my heart. - J.T. -


Dear J.T.,

The 28 trees on the list we've been sending out (scroll down to read about it, and download a copy) are not the "last word" but a great start.  That list was compiled from the choices made by city foresters with long experience in planting and maintaining our urban forest. Beauty is valuable in that forest but secondary to adaptability, dependability and availability.

The katsura is an outstanding tree. If we added it to the list, it would be in the group that requires unrestricted root space, in a large lawn or park. It would not thrive with its roots trapped between street and sidewalk.

That places it with dawn redwood, which is big but shouldn't be discounted as a shade tree, or a boulevard tree. People walking near us the day we caught sight of dawn redwoods as street trees in lower Manhattan gave us a wide berth when we both froze in place, open mouthed and staring. Yes, the huge, fluted trunks rising from openings in the pavement had been limbed up for clearance as they grew but it did not detract from their beauty.

Many trees are groomed for their future use by the grower, so that there are a number of trees most people wouldn't even know in their natural form. Grooming often includes removing lower limbs as the tree grows, even on a tree that would otherwise be branched right to the ground. Pin oak, linden, hawthorn and magnolia all have ground-sweeping skirts, in nature. Yet the first two are commonly used as street trees, so we produce them without branches below nine feet to permit pedestrian and vehicular traffic. The last two are limbed up because we like to grow gardens and lawn beneath.

Chances are that when there were dawn redwood forests, individual trees lost their lower limbs just as white pines do in dense stands. We can't know this, since dawn redwood disappeared from the wild centuries ago. The species survived as one cultivated grove in China, eighteen trees widely spaced. All those we plant today come from that one remnant of ancient times.

Or download our more detailed list:

In the Wake of Emerald Ash Borer: Ash tree replacements

As the non-native insect, emerald ash borer (EAB), continues killing billions of ash trees (Fraxinus species) throughout eastern North America, there is as yet (2014)  little we can do to stop it. Here is a list of trees suitable for replacing an ash at streetside or in your yard. It was compiled from the choices offered by city foresters in our area, at the epicenter of the emerald ash borer plague.
On our list we have included detailed descriptions of the trees. For more about emerald ash borer, search those words here on our site and visit the U.S. Forestry Service  EAB information page where you can learn about EAB status in your area, and the latest on its control.
download the ash tree replacement list in pdf


In search of rare seeds

Dear Janet,

Do you know a source where I can find seeds that not everyone seems to stock?  I am especially looking for seeds of a plant called Jamaican sweet pea. - M.B. -

Dear M.B.,

How about Old House Gardens, a mail order firm specializing in heirloom bulbs and plants? You can find them at

We're not familiar with the common name Jamaican sweet pea. Do you have the plant's scientific name, or more clues to go by? Numerous plants can share a common name. So without a scientific name, you might find nothing or be surprised to meet an unexpected plant when you sprout the seed you buy.

Short report

Are there more insects where there is mulch?

When people scrape aside mulch, point and say, "Look at all those bugs!" We say, "Just don't look. The vast majority aren't hurting but helping you and the garden."

There may be more total types of insects in a mulched garden but probably not more insects overall. Mulched soil is cooler and more moist than bare soil, better for root growing and also more attractive to certain insects, decomposers that break organic matter into soil-enriching minerals and humus. Other insects come to prey on the decomposers and may also stay to hunt plant-eating insects in the area.

Mulch does not provide homes for ants or termites unless it consists of abnormally large pieces of wood -- chunks or logs rather than chips.

Green thumbs up

to the rain that finally came. Now the trees, shrubs, bulbs and perennials we've planted in September and October can use the season as they should, to get the jump on next year.

Green thumbs down

to planting and walking away. No matter how big and self sufficient the tree seems, mulch it well then keep the new root ball and surrounding soil moist until the ground freezes.





 Originally published 10/23/04