Growing Concerns 730: August, natural wooded area...

... hedges of juniper and other shrubs, vertical mulch, dividing, edging, mowing


Tip of the week:

Vertical mulching can cure hard packed soil. It creates vital pathways for air and moisture to reach roots. Fall is a good time to employ this technique.

Many holes about three inches in diameter are drilled into ground beneath a tree's branches. Compost and slow release fertilizer may be placed in the holes so each contains an airy, rich moisture-retentive mix where roots can grow. Microorganisms that establish there move laterally from the holes into surrounding soil, gradually loosening the spaces between.

 

In this issue:

Think succession for success on wooded lot: Basics for creating a natural, wooded area.

Native juniper best for a hedge in sun and wind.

Twiggy, fast deciduous shrubs for hedge in part shade.

Vertical mulching frees trees from hard packed soil.

Dig and divide any time after summer heat breaks.

Good time now to re-cut trenched bed edges.

Proper mowing height and tips for various lawn grasses.

High time to seed and plant, or cut back tomatoes and other veg.

Natural woods, you can enjoy them and also use them as models for your own wooded lot.

Natural woods, you can enjoy them and also use them as models for your own wooded lot.

Wooded lot design basics

I am trying to naturalize a side yard that was wooded, but the builder used as a parking lot for his trucks while building our house. We've planted some evergreens and deciduous trees, but want to fill in between them with woodland type plants. The soil is very dry and rocky. Any suggestions?  Would hemlock or bayberry (Myrica) work well there? - D.C. -

 

Plant choices for a wooded lot are right up our alley. We're surrounded right now by materials we use in teaching about native trees, shrubs, woodland wildflowers and their settings. That's because we're preparing our parts of a Natural Gardening and the Wooded Lot workshop (check our calendar for these workshops or contact us to invite us to present these sessions for your group).

Here are excerpts and distillations from that workshop.

 

Succession succeeds

You're smart to make woody plants your first priority. To preserve the health of existing desirable trees or add or remove trees and shrubs from a wooded lot, take your cues from succession. That's the natural process that Nature follows to create, age and change a woods.

You can learn more about succession in the books Woodland Stewardship: A Practical Guide for Midwestern Homeowners (by Baughman, Alm, Reed, Eiber and Blinn, University of Minnesota Extension) and The Forests of Michigan (http://www.press.umich.edu:80/titleDetailDesc.do?id=12017) (by D. Dickman and L. Leefers, University of Michigan Press) or under "Forests are an ever-changing ecosystem" in Attracting Woodland Wildlife: A Primer (http://www2.dnr.cornell.edu/ext/info/pubs/Wildlife/attracting_woodland_wildlife_goff.htm).

Copying from natural succession, we let the first woody plants on a site improve the soil for later species. If those pioneers grow well, they convert minerals, air and water into organic matter, that falls on and enriches the soil.

 

Soil condition is critical, and improve-able

Compacted soil is hard on the gardener who wants to plant there but even harder on tree roots in that soil. Roots cannot get enough oxygen or water through the densely packed pores in a squashed soil. So consider hiring a tree care firm to loosen the soil via "vertical mulching."

Plot great paths

Next, map out paths and places for visiting humans and wildlife to rest and enjoy that little woods. Think about what you will do when you walk there and your angles of sight as you look in that direction or approach from your home. Create entrances and invitation, suspense and surprise with the placement of your paths and sitting areas, and flow of your paths.

If walks in the woods soothe you, be sure to create paths through your own wooded lot. It doesn't matter if the lot isn't big enough to have a path that goes on and on as it might in a large woods. Give your paths twists and eye-catching features that recreate the feel of the big woods. Use photos like this of natural woodlands as your guide.

 

Mulch, and more mulch, naturally

Mulch the paths heavily, right away. Keep deep mulch away from tree trunks but add it liberally over your travel routes. That helps prevent additional compaction from foot traffic. It also provides a places that nurture and spread important soil-building organisms -- everything we don't like to name plus worms, beneficial fungi and more. If you add mulch now you will find that even as early as next spring the soil under the path and several inches to a foot out on either side will be looser and easier to dig. The effect continues outward, season by season.

Let fallen leaves lay on the floor of your little woods, and spread more as you get them when neighbors rake this fall. Hold a leaf layer in place with sticks laid on top if the area is very windy and you're concerned about leaves blowing back to your neighbors.

 

Choose new plants for their best features

Then check the qualifications of plants you' might add. That means looking into leaf characteristics, as you've probably done to discover the featheriness of evergreen hemlock (Tsuga canadensis) or that brush-past fragrance of bayberry (Myrica pensylvanica). Think, too, about color in the fall, bloom and berries, mature height and spread, and growth rate.

In answer to the hemlock or bayberry question, look into something about each plant that's vital to creating an easy, pleasingly natural woodland. That's the plant community to which your potential additions belong.

 

What's grown there naturally is a clue about what to add

Hemlock's normal associates are sugar maple, beech, yellow birch, white pine, arborvitae, rhododendron and fir. Bayberry often occurs naturally with sandcherry, chokeberry (Aronia species), scrub oak and sweet fern (Comptonia peregrina) in dry soils, and elderberry (Sambucus species), hazel alder (Alnus rugosa) and hardhack spirea (Spiraea tomentosa) in wetter spots. If any of these plants are there already and doing well you have a first indication that the new addition might thrive in that soil type and exposure.

Perhaps more importantly, you can expect naturally associated plants to help each other. They live compatibly, drawing from different nutrient banks rather than competing and each one fosters soil microbes that are beneficial to other plants in the community.

 

Serviceberry (Amelanchier canadensis) is an understory tree with spring bloom fragrance, coppery fall color, and pretty berries that are great eating if you can beat the birds to the harvest. Serviceberries taste like raspberries with the texture of blueberries.

Serviceberry (Amelanchier canadensis) is an understory tree with spring bloom fragrance, coppery fall color, and pretty berries that are great eating if you can beat the birds to the harvest. Serviceberries taste like raspberries with the texture of blueberries.

Great resources

Much of the information you need for putting native plant communities together is in Native Trees, Shrubs and Vines for Urban and Rural America by Gary Hightshoe (1988, Van Nostrand Reinhold Books). Although the book's out of print, secondhand copies are worth seeking. It's a measure of the value of this book's information that used copies may fetch a higher price than they did new.

You can also find some of this kind of information by searching under the plant's scientific name at plants.usda.gov/java/ for North American natives, and Missouri Botanical Garden's plant finder (http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder.aspx) for landscape plants both native and foreign.

 

Wildflowers last

Wait to add smaller plants such as woodland wildflowers after your upper- and middle story plants are selected and placed. Then, choose them as you did woody species, for their fit with the community and appeal to your senses. At this step you can use Perennials and Their Garden Habitats (by Richard Hansen and Freidrich Stahl, Timber Press), the websites listed above, and wildflower guides such as Michigan Wildflowers in Color (by Harry C. Lund, Thunder Bay Press).

When you've completed your woody plant work you can write again or post questions on our Forum.

Hedging for privacy

A coworker asked me to recommend an evergreen tree for his yard. It's on the edge of his property and his neighbors are close, so he wants an evergreen for privacy. The spot gets full sun and is very windy during the winter.

He originally had fraser firs but they suffered a lot of windburn. He also has a couple black spruces, which also got some winter damage. He is willing to 'baby' the black spruces with a wind screen and Wilt-pruf for a couple winters if they will be okay once established (he doesn't want this to be an annual requirement). Any ideas for a tree I can recommend? - M.G.N. -

Virginia juniper or eastern red cedar (Juniperus virginiana) occurs naturally in windy, open areas such as along Interstate Highways. Named varieties like 'Spartan' (at right) make good hedges in sunny, windy spots. Before you plant them, consider the fact that they are the winter-time host for diseases of crabapple and hawthorn called *cedar-apple rust and cedar-hawthorn rust. So if crabapples or hawthorns are on a site, avoid planting Virginia juniper nearby or use its rust-resistant varieties such as 'Burkii' or 'Pyramidalis.'

Virginia juniper or eastern red cedar (Juniperus virginiana) occurs naturally in windy, open areas such as along Interstate Highways. Named varieties like 'Spartan' (at right) make good hedges in sunny, windy spots. Before you plant them, consider the fact that they are the winter-time host for diseases of crabapple and hawthorn called *cedar-apple rust and cedar-hawthorn rust. So if crabapples or hawthorns are on a site, avoid planting Virginia juniper nearby or use its rust-resistant varieties such as 'Burkii' or 'Pyramidalis.'

*cedar-apple rust and cedar-hawthorn rust

Isn't it rewarding to be a resource to others? We gardeners do make a difference.

Given a sunny site and a hankering for evergreens,  we always put Virginia junipers (Juniperus virginiana) on the top of the list. There are varieties such as  'Manhattan Blue' and 'Emerald Sentinel' that are wonderful in terms of color and form, plus most members of this native North American species have great wind tolerance and respectably fast growth.

If the planting site has some combination of shade and wind we suggest a tall hedge of twiggy deciduous plants. That's more sensible than wasting money and time pampering evergreens. It also eliminates the burden of living with an imperfectly-suited species, in which we still must face occasional plant replacement no matter how old and well established the hedge. Snowmound spirea (old-fashioned Spiraea x Vanhouttei) at 8 feet tall, privet at 10-15 feet and burning bush are all candidates. They're twiggy enough to be visual barriers even in winter, amenable to pruning and tolerant of tough growing conditions including wind.

Allow burning bushes (Euonymus alatus) to grow into a hedge without pruning and they will form a wall 8 to 12 feet tall. They are not only a good privacy screen during the growing season but twiggy enough to block at least some prying eyes even as the shrubs lose the last of their leaves and stand bare in winter. Note: Burning bush has invasive tendencies and has become a problem in some areas including some New England States. There are native alternatives, such as chokeberry (the unfortunately named but beautiful Aronia species).

Critical tree care: vertical mulching

Vertical mulching is a process that creates vital pathways for air and moisture to enter the soil and reach plant roots.

 

Drill

Typically, holes about three inches in diameter are drilled into the ground beneath a tree's branches, creating a grid of holes 12 to 18 inches deep and 18 to 24 inches apart. Compost or sand along with slow release fertilizer may be placed in the holes so each contains an airy, rich moisture-retentive mix where roots can grow. Microorganisms that establish there move laterally from the holes into surrounding soil, gradually loosening the spaces between.

 

Fracture the soil with air pressure

Sometimes, compressed air is forced into each hole, in place of or after adding the back-fill mixture. A stream of air forces the soil to fracture outward from the hole.

Trees often react to airification as if they have been fertilized, even if no fertilizer was used. This is because their roots have gained the benefit of more air and water.

If compost and/or fertilizer was poured into the hole, the air stream pushes water- and nutrient-bearing organic matter into the gaps. Then, soil animals move more quickly into the adjacent soil.

 

Certified arborists can do this for your trees!

Look up tree care firms in an area phone book or arborists certified through the International Society of Arboriculture (www.isa-arbor.com). Ask about vertical mulching. Some use compressed air to clear away soil without drilling, in the form of an air spade (http://www.youtube.com/watch?v=WTIobRz_2TU) or air knife (http://www.rhizosphere.co.uk/AirKnife.htm).

Steven spent time in the field with ISA-certified arborist Bernie Car, who was using an air knife to loosen compacted soil. We were impressed with Car's work and his ability to explain its why's and how's. We're also impressed by the wealth of information about soil and loosening techniques on his company's website http://treeandshrubcare.info/.

Right: Bernie Car, an arborist from  Organic Air (Norwalk, Ohio), uses an air knife to penetrate compacted ground 30 inches deep and then force in air to fracture the soil in all directions from that hole.

 

This week in our gardens

Grow with us! This week we will:

Dig and divide

Start digging and dividing perennials that have outgrown their bounds or have become crowded and sparser of bloom than they once were. The soil is so receptive when it's warmer than the air for some portion of each 24 hour period. Even better when at this time of year that temperature differential exists plus the soil's charged with rainwater, too. Both conditions are common in late summer, after the nighttime heat breaks. Then, transplants "take" like magic.

 

Cut- or clean up edges on beds

Re-cut and clear out all the trenched edges between flower beds and adjacent lawns. Once the nights cool in late summer and rains begin, lawn grows ferociously and can infiltrate a flower bed or groundcover across portions of that trench that filled during summer with moisture-holding material or soil. Spending 30 minutes edging now can save us an hour of weed extraction next April when we might be dealing with lawn grass grown two feet into the bed.

 

Avoid drowning plants now that late summer rain's come

Empty all the cache pots and saucers under our containers after a rain, so roots at the bottom of the container won't rot.

 

Try to stop the lawn-scalpers!

Argh! to the lawn mowing crews who have not had enough to do all this dry summer from mowing lawns too short as it begins to grow again. Lawn height should be:

  • 2-1/2 to 3 inches tall in spring or fall and 3 to 3-1/2 inches in summer if it's bluegrass or tall fescue (Iowa State University Extension tells the straight story on mowing)
  • • 2 to 4 inches tall if it's that sturdy buffalo grass used in some Great Plains States.
  • • 1/2 to 3/4 inches tall if it's creeping bentgrass. (Many Midwesterners hate this stuff as "the invader you can't get rid of!" but it does have its uses  -- which is why it's included on mowing charts such as this from University of California.
  • • 3/4 to 1 inch tall during spring, summer and fall on what you find in many Southern yards, a bermudagrass lawn. Mow that bermudagrass up to 1/2 inch taller December through February.

These are the heights each type of grass needs to be healthy and shade out weed seedlings that try to take hold in open spots. These also usually have the effect of producing the very best bare-foot experience around.

(Take note, J.W., you can print this out and give it to your son who asked for lawn mowing guidance. Say it's not only height that matters but that he not take more than 1/3 of the leaf surface off at any one mowing. So during fall and spring when grass grows faster, it needs more frequent mowing.).

One other basic mowing guide:

Keep your blades sharp. Mow often and let clips fall to decompose, rather than mowing infrequently so that clips fall in clumps to smother remaining grass.

 

Green thumbs up...

...to people who accurately read the first dewy morning in late summer as the sign that nighttime heat has broken. (Hereabouts, it happened just over a week ago, right on schedule in the third week of August ). The best thing ever is if we jump on that indicator and begin right away to sow seeds, plant, divide, transplant, and then receive the greatest blessing a gardener can receive -- a rainy follow-up. It does often happen at this time of year!

Green thumbs down...

...to expecting much if you cut back warm season vegetables like tomatoes, pepper or squash now. The plant will need about three weeks to form new shoots and flowers. Even if you have that much time before temperatures will drop below the plant's comfort zone, and even if those new flowers do set fruit, the remaining growing season may not be long enough for that fruit to ripen.

Oh the sprawl of it all! At summer's end a tomato, squash or bean plant may crowd nearby plants that are in the process of ripening fruit. Or the sprawling past-prime plant may be shading neighboring cool-season crops just coming into their own. It's best to remove the offending galoof. Then in the freed-up space, plant cool-season crops that can come on during fall. Broccoli, spinach, lettuce and peas are all possibilities.

Oh the sprawl of it all! At summer's end a tomato, squash or bean plant may crowd nearby plants that are in the process of ripening fruit. Or the sprawling past-prime plant may be shading neighboring cool-season crops just coming into their own. It's best to remove the offending galoof. Then in the freed-up space, plant cool-season crops that can come on during fall. Broccoli, spinach, lettuce and peas are all possibilities.

 First published 8-25-07