Best time to plant trees
Today is Arbor Day, that milestone that reminds us that late April is an ideal time to add a new tree – or trees – to the landscape.
Trees provide a variety of benefits including cooling summer shade, habitat for birds and beneficial bugs, protection from unwanted views, oxygen to the air, carbonaceous services to mitigate climate change, and the beauty of blossoms and fall foliage.
Pennsylvania’s temperate climate gives us a wide variety of trees. Morton Arboretum in Illinois offers these five tips for choosing the “right” tree for the “right” spot:
1.) Determine the amount of heat and type of light the area is receiving, then stick with types that match those conditions.
2.) Consider soil drainage. To test, dig a planting hole and fill it with water. If the water level hasn’t dropped significantly within two hours, either choose a better-draining spot or amend the soil with compost to create a raised planting bed.
Or stick with species that tolerate wet soil.
3.) Lean towards trees whose natural environment is as similar to your site as possible, ie forest types when you have shade and moisture vs. open grassland types when your site is in full sun and on the dry side.
4.) Give the tree enough space. Know how tall a tree will grow over the long term and make sure you have enough space to avoid unnecessary pruning, stunted growth, shortened tree lifespans, and even property damage from upended sidewalks and branches growing into power lines.
5.) Pay attention to certain aspects that are relevant to your location, such as: B. Types that deer do not favor when gardening in deer country, the possibility of excess salt in the soil when planting along a roadway, and whether your soil is acidic or alkaline and rich or poor in essential nutrients.
- See Penn State’s soil testing website
Here are a few short lists geared toward south-central Pennsylvania to get you started:
12 Good Native Trees: American Fringe Tree, River Birch, Blackgum, American Dogwood, Sweetbay Magnolia, Serviceberry, Red Maple, Red Oak, White Oak, American Hornbeam, Redbud, Silverbell, Hawthorn ‘Winter King’.
13 Small Flowering Trees (under 25 feet): American Dogwood, Kousa Dogwood, Cornelian Dogwood, Stewartia, Crabapple, American Fringe Tree, Redbud, Serviceberry, Sweetbay Magnolia, Seven Son Flower, Crepe Myrtle, Japanese Tree Lavender, Witch Hazel.
12 shade trees ranging from 25 to 50 feet: Hornbeam, Black Eucalyptus, Red Maple, Freeman Maple, Paperbark Maple, Katsura, Dwarf Linden, Dutch Elm Disease Resistant American Elm (Accolade, Jefferson, Colonial Spirit, Valley Forge, etc.), Silverbells, White Oak, Yellowwood, Ginkgo.
12 of the Best Evergreen Conifers and Conifers: Hinoki Cypress, Alaskan Weeping Cedar, Greenthread/Goldthread False Cypress, Oriental Spruce, Serbian Spruce, Norway Spruce, Arborvitae ‘Green Giant’, Japanese Umbrella Pine, Bosnian Pine, Eastern Red Cedar, Dawn Redwood, bald cypress.
Trees Suitable for Our Future Heat: Sycamore/London Sycamore, Blackcap, Dutch Elm Disease Resistant Elm, Freeman Maple, Ginkgo, Hackberry, Japanese Zelkova, Kentucky Coffee Tree, Red Maple, Red Oak, Scarlet Oak, White Oak, Sweetgum, Yellowwood (larger shade trees over 40 feet tall); American hornbeam, Persian parrots, river birch (medium-sized 25 to 40 feet); American dogwood, American smoke tree, cornel dogwood, crab apple, crape myrtle, hawthorn, redbud, service berry, sweetbay magnolia (flowering trees under 25 feet); American Holly, Austrian Pine, Bald Cypress, Chinese Juniper, Dawn Redwood, Eastern Red Cedar (evergreens or conifers).
- See George’s tree-by-tree profiles
The final step in your Arbor Day duty is to get your new trees properly planted.
Free any circling roots before planting (especially for trees in containers); Avoid planting too deep (a major cause of early tree death); Once the root ball is in the hole, remove all burlap, twine, wire baskets, or other transportation aids, and keep the soil around and under the root ball moist at all times (especially for the first year or two).
Normally, a new tree does not need to be fertilized. Base any fertilizer application on recommendations from a soil test.
And aside from removing broken branches, don’t prune before or immediately after planting. Begin pruning to shape the tree in its second year.
- Read George’s tips on nine things that can go wrong when planting trees
Avoid cutting deep lips around the perimeter of trees to avoid severing roots trying to spread.
Why “tree digging” is a bad idea
You may know by now that mulch piled up on tree trunks — often referred to as “mulch volcanoes” — is bad for trees.
The excess mulch traps moisture on the bark of the trunk, encouraging it to rot. Additionally, layers of mulch thicker than three or four inches can encourage girdling of roots at the base of the trunk, harbor bark-chewing rodents, and impede the level of oxygen reaching the tree’s roots.
Ohio State Extension educator Joe Boggs says another, lesser-known mistake in tree mulching can be just as damaging — the practice of creating “tree ditches.”
Tree ditches are when gardeners cut a lip several inches deep around the perimeter of a tree bed. The idea is to create a definition of these ring-shaped beds and create a mini-wall that will keep the mulch inside the ring.
“Unfortunately, overly enthusiastic excavation produces ‘tree digs,’ which often cause root damage and may even involve a concerted effort to sever roots growing outside the excavation zone,” Boggs writes in a follow-up to Ohio State’s Buckeye Yard and Garden Online website extension.
Boggs cites studies showing that the majority of a tree’s root system grows well outside of a tree’s drip line — the area covered by its canopy. If gardeners cut too deep around the perimeter of the mulch ring, they risk severing roots that are growing farther out.
“Severing these roots creates a concentrated root mass within the mulch ring, where resources like water and nutrients can be used up more quickly,” says Boggs.
This can shorten a tree’s lifespan, make it more susceptible to drought damage, and leave the tree vulnerable to infection at wound sites.
Both mulch volcanoes and tree ditches are “insidious” problems, says Boggs — ones that cause subtle and long-term effects rather than obvious, immediate problems.
“Maybe that’s the problem,” he says. “If trees died instantly, people would stop the mulch craze.”
When digging or edging the mulched perimeter of a tree, do it lightly and carefully to avoid severing tree roots, advises Boggs.
Topping up with compost is often enough to repair small, flat spots in the lawn.
How to fix low spots in the lawn
Sometimes an otherwise smooth and level lawn develops ridges, pits, and other low spots.
While small ones aren’t a problem, larger ones can result in twisted ankles, pose a fall hazard, or provide concussive impacts while mowing.
Significant lows can also indicate a larger problem that needs to be addressed.
A sudden, large bottom may indicate a sinkhole, subsidence from previous mining activity, or a ruptured water or sewer line.
Gradually worsening furrows could be a sign of erosion caused by storm runoff.
In other cases, sunken spots are the result of animals tunneling under them, such as voles, moles, and marmots.
Most of the time, however, low points are caused by subsidence – usually in areas where a garden or landscape bed used to stand and especially where a large tree has been removed. When the roots of a felled tree fall off, the ground often sinks.
Spring is a good time to start repairing those deep spots and ridges.
One approach is to level compost or topsoil over the low areas. This method, called “top dressing,” is easiest when the indentations are shallow.
Up to half an inch of compost or topsoil can be added without smothering the lawn. In small doses like this, the grass crowns will elongate and grow through the added soil.
If one time doesn’t solve the problem, you can do top dressings every spring and fall until the lawn is level.
In larger and deeper areas – or if you want to level a lawn immediately – the second approach is to dig up the low spots and fill in underneath.
Cut around the perimeter of the low spot and dig under it to remove patches of grass that are two to three inches thick. Put the sod aside in a shady place.
Then fill in the excavated area with enough topsoil to bring it almost to level. Replace the sod, tamp lightly, and then water well.
When you’re done, the area will be level right away and may not even look disturbed.
Keep the area moist for several weeks to allow the sod to re-root.
- More tips on when to do what: George’s book, Pennsylvania Month-by-Month Gardening.
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