Oaks got flare!

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A red oak with a beautiful, healthy root flare. Even very young trees have a flare, although it can be less dramatic while the roots are still small. For the vast majority of trees (palms are an exception), it's true that if you can't see a flare, the tree's planted too deep. Too deep is trouble! 

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Best trees have wide base

At a conference one day, during a discussion about proper planting depth for trees, we said we use the trunk flare as a guide. That is, we know a tree's at the correct depth when we can see that area where the trunk widens as it joins the roots.

"What about oaks?" One person asked. "Oaks don't have flares."

Oaks certainly do have flare (at right, a red oak). If you have an oak without a visible flare, one that looks like a stovepipe at ground level, it's too deep. Start digging around that trunk to lower the grade or lift and re-set the tree if it's a new planting.

Train your gardener's eye to look for flare on all trees. There may be exceptional species (palm trees, for instance), and flare may be less pronounced when a tree is young, but there is indeed a flare on every tree species we know that's likely to be in northern landscapes.

See tree flares that are works of art and how the flare develops in What's Coming Up Issue #136.

How that oak became so big:
Tree planting basics

(You'll probably want more photos...)


Summary of planting! For determining growth rate, there's help in What's Coming Up50.

Tree planting steps

One: Dig a planting hole.

Two: Check planting depth by locating the tree's root flare.

Three: Position the tree in the hole.

Four: Fill the bottom third of the hole.

Five: Remove all wrappings from the top part of the ball.

Six: Finish filling the hole.

Seven: Stake the tree only if necessary.

Eight: Create a watering well.

Nine: Mulch the tree's root zone.

Ten: Follow up with water for at least a year.

One: Dig a planting hole.BirchBPlanting68.jpg

Dig a shallow, broad hole, only as deep as the root ball but much wider.

("Okay I got it. Jump me to step two.")

(Take me back to the list of ten steps.)

Right: We measure the ball against our spade to figure how deep and wide to dig. Always much wider than the ball, never deeper.

The most important and numerous roots a tree grows are in the top five- to fifteen inches of soil and grow horizontally, not down. The faster a tree's roots can spread out of the original root ball and regain their pre-transplant rate (elongating twelve to 24 inches per year), the more self sufficient the tree becomes and the better its long term outlook. So remove competing weeds and loosen the soil fifteen inches deep at least two feet beyond all sides of the root ball.


Digging the hole, misconception number 1:

Don't believe that, "Soil should be loosened under as well as around the root ball."

People thought root systems were mirror images of tree branches, until researchers excavated and examined thousands of tree root systems on behalf of organizations such as the International Society of Arboriculture and the USDA's Forestry Service. What they found is that very few roots grow down from the original root ball, or from the lower third of the root ball. So loosening the soil under a root ball is unnecessary.


Digging the hole, misconception number 2:

Don't believe that, "Subsoil must be loosened to improve drainage."

Loosening the subsoil is only useful if you can break through to free-draining layers. In that case, loosen subsoil everywhere except where the ball will sit. If there is no better drainage to be obtained directly below the tree, place a tile to drain the base of a hole or trench the perimeter of the bottom of the planting hole so the root ball will sit on a "tee" above any excess water.

Avoid loosening below the ball so the tree will not settle below grade. Read on, for why this is to be avoided..

Two: Check planting depth by locating the tree's root flare.

The flare is where the roots spread from the trunk base.BirchCPlanting69.jpg

If you cannot see the root flare at the top of the root ball or pot, you may have to remove some soil from the top of the root ball.

Right, we peeled back the burlap and removed  almost 4 inches of extra soil that had been added over the roots and against the trunk. No, it didn't hurt the tree to do this, it helped. We can say that not only with the confidence we had on planting it 10 years ago, but the satisfaction we feel in seeing it today, large and healthy.

Wadded burlap atop a root ball or extra soil at a pot's surface may mislead you, so that you plant a tree too deep. Even a few inches of extra soil over the roots can slow their growth and stunt the tree, and any soil against the base of the trunk can slowly but surely kill the tree.

("Okay I got it. Jump me to step three.")

(Take me back to the list of ten steps.)


Check planting depth, misconception:

Don't believe that, "Always plant a woody plant 'at the same level it was growing in the pot.'"

This is no longer a safe guideline. Even if there were not other reasons to peel back and remove burlap from a root ball, it would be essential to do so to check for the root flare. This may be the newest of the news in this article.

Too-deep planting has become an epidemic. For years, we blamed this problem on those who planted trees, saying, "You set it too deep, or let it settle!" We know now we were wrong in many cases. A new horticultural term has been coined and joint committees of tree producers, landscape architects and landscape contractors have convened to address the primary problem, trees "harvested too deep."

How a too-deep epidemic happens

Trees are planted too deep throughout the course of production.

  • At the seedling or grafted-liner stage, a six-inch sprig may be planted a bit deep to hide the crook of the graft union or to satisfy an untrained planter's notion that deeper planting will make the tiny twig more stable.
  • Then as it's moved from starter pot to larger containers or to a field, or balled and burlapped from a field and placed in a container for easy handling, it may be set an inch or more too deep at each step.
  • At the end of the process a tree may have several to many inches of soil over its roots, burying the trunk. They have been "harvested too deep."

Given the normal wide, shallow profile of a tree's roots, too-deep production planting means that trees lose even more roots than they should when dug from a field. (See diagram.) (Diagram's not here yet! See "Sponsorship, above!)


Avoid buying "too deep"

In recognition of this disastrous situation, the most savvy tree buyers now carry a metal skewer with them as they choose trees in a nursery. The buyer inserts the skewer vertically into a root ball to determine how much soil there is above that plant's big, main-order flare roots. If the skewer penetrates to two inches before hitting wood, that may be judged unfortunate but common and correctable. If the skewer goes deeper before touching roots, the buyer will reject the tree.

Three: Position the tree in the hole.

Now recheck the depth of your planting hole. It should be no deeper than the distance between the root flare and the bottom of the root ball. If you were misled by a tree that was harvested deep, add soil at the bottom of the hole and pack it firmly. Then set the tree a bit high to allow for settling.

To straighten the tree, look at it from several angles. Correct any lean by using a long-handled shovel to tip the ball, then pack soil to maintain the new position.

 ("Okay I got it. Jump me to step four.")

(Take me back to the list of ten steps.)


Don't use the trunk as a lever to move a tree

A tree's limbs, trunk and roots are not designed to support the weight of the soil in its root mass. Lifting a potted or B&B tree by its trunk or branches or using them as a lever to reposition a root ball can break roots within the ball and injure the cambium where you gripped it. Damage may show right away or may not be apparent until years later. So avoid it altogether. Lift a tree by its root ball, never by the trunk.


Positioning for depth, misconception:

Don't believe that, "Trees should be planted high, to be above wet soil and poor drainage."

It is true that in compacted urban soils a tree has a better chance of survival if 1/3 of the root ball is above grade. But where drainage is adequate the tree will grow better and live longer if planted at ground level.

Don't let your tree be one of the increasing number that survive a warranty period above grade only to die soon after of root loss or toppling. Plant high only in poorly drained areas where you cannot correct that situation. When you must plant high, create a raised bed at least four feet wider in diameter than the tree's root ball to insulate the exposed shoulders of the root ball and provide a place for roots to grow.

Four: Fill the bottom third of the hole.

Gently but firmly pack soil around the bottom third of the root ball. This will keep the tree from shifting.

Five: Remove all wrappings from the top part of the ball.

If the tree is balled and burlapped (B&B), cut and remove all string, burlap and wire from around the trunk and top third of the root ball. Use bolt cutters and heavy scissors.

Be careful not to damage the trunk or roots in the process of removing cords, clipping wire or slicing burlap.

("Okay I got it. Jump me to step six.")

(Take me back to the list of ten steps.)


Several important reasons to "bare the ball:"

  • First, drought is the primary cause of new tree failure and exposed burlap acts as a wick, drying out the soil next to the root ball.
  • Second, encircling string and wire can girdle and kill the trunk and roots. It may be easy to see how a tight circle can kill a trunk but even a wide wire basket or burlap-cinching plastic cord can kill the tree in time. Those losses are often worst, coming as the tree finally fills its place in a landscape.
  • Third, roots that bend when they meet burlap or wire, remain bent and often become girdling roots. Wire and cloth openings that are smaller than a fully grown flare root -- perhaps several inches in diameter -- may admit young roots only to girdle them later.


Remove all wrappings, misconception number 1:

Don't believe that, "We mustn't disturb the root ball."

It is true that root balls may crumble if unwrapped and manhandled, but it is a risk we must take to address the deep harvesting problem. A Washington State DNR tree planting brochure says it best, "Don't disturb the root ball is a myth. The truth is most root balls need corrective pruning prior to planting." Corrections may be removal of soil or pruning circling roots and adventitious roots above the flare.


Remove all wrappings, misconception number 2:BirchEPlanting71.jpg

Don't believe that: "It's not necessary. Burlap and cord rots quickly and wire cages rust away."

Since burlap and twine rot quickly under irrigation in a nursery, everyone figured they would act that same way in the landscape. When wire cages came into use, it was assumed they would rust. Tree planters embraced these notions, glad they could thus avoid some steps in the planting process. Then they maintained that position despite lacking research to support either claim. Time and an overwhelming number of problems associated with decades-old twine, long-lasting new-age burlap and cages have now overturned both assumptions.

Above: We dig the hole wide enough to fit our arms around the ball as we lower the tree into the hole and set it straight. There also must be enough space to do what Janet's doing now -- reaching in alongside the rootball with wire cutters and knife to remove the wire and the burlap that would otherwise impede root spread.

Six: Finish filling the hole.

Fill the remainder of the hole, adding soil a few inches at a time and settling it with water to avoid large air pockets

 ("Okay I got it. Jump me to step seven.")

(Take me back to the list of ten steps.)


Filling the hole, misconception number 1:

Don't believe that, "Get rid of the excavated soil and replace it with good soil and peat."

This is not necessary. A tree will eventually outgrow any hole you dig. The single most important amendment you can add to that eventually huge root zone is air, by loosening the soil in an expanding circle as the tree grows.


Not only unnecessary but root of later problems

Some studies revealed problems from amending the backfill. Roots circled within the enriched soil rather than growing beyond the edges of the planting hole, limiting the root system and creating girdling roots. Soil amended with organic matter settled, exposing the sides of the root ball and allowing roots there to dry out. Based on these studies we are sometimes warned against amending the backfill.

Some experts doubt the relevance of those test results. Researchers contributing to the book, The Landscape Below Ground explain, "Those studies on sandy agricultural soils provide little insight into urban situations with compacted clayey soils."

We add compost to backfill around trees in poor, hard packed soil to keep that soil from settling back into an airless mass, with excellent results.


Filling the hole, misconception number 2:

Don't believe that, "Add some fertilizer or rooting hormone as you backfill."


Studies show no benefit to fertilization at planting and some danger of encouraging shoot growth at the expense of root growth. So fertilizer is not recommended until a tree has been in place for a year. As for rooting hormones, vitamins and beneficial fungi, although they have been around since the 1940's, the jury is still out on whether they have any positive effect. Trees treated with these products fail to show any significant positive response as compared to untreated controls. So if you want to save a few dollars, skip the B vitamin, microrrhizae and seaweed solutions.

Seven: Stake the tree only if necessary.

Well-grown trees with root balls that meet nursery standards do not need any support in most home landscape situations. Studies have shown that trees establish more quickly, develop a stronger trunk and have better roots if they are not staked.

("Okay I got it. Jump me to step eight.")

(Take me back to the list of ten steps.)


Sometimes reason to stake for a year

However, you may decide to stake where reckless lawn mowing, vandals or extreme winds are concerns. To ward off mowers and weed whips, you might circle the tree with stakes. Deter vandals or avoid wind damage by flanking the tree with stakes and using wide strap-like material between stakes and the trunk to prevent extreme movement. Remove stakes and ties after one year.

A new staking system for very windy or severely sloping sites is put in place when the root ball has been unwrapped but before the hole is filled. The ball itself is strapped with wide, biodegradable belts that lap over its shoulders of and attach to stakes driven into the bottom of the planting hole.


Stake the tree, misconception number 1:

Don't believe that, "Stakes should immobilize the tree."

The editors of the 1957 Taylor Guide to Gardening had no idea of the long-term consequences of their advice to "...stretch three tight guy wires fastened to stakes..." to support a new tree. Research has tied staking to a number of problems, starting with the fact that a tree which could not sway as it grows develops a weak trunk, prone to snapping as the tree matures.


Eight: Create a watering well.

Use soil from outside the planting hole to construct a one inch high levee around that spot. You should be able to pour a bucket of water at the base of the tree and see it remain within the root zone long enough to be absorbed into the ball and the soil around it.

("Okay I got it. Jump me to step nine.")

(Take me back to the list of ten steps.)


Keeping the ball moist is the most important step in establishing a new tree, but is more difficult to do than you may imagine. The root ball has a greater density of roots and is often of a different consistency than the surrounding soil, so it dries out more quickly than the ground around it. A watering well insures that the ball is wetted, rather than bypassed as water runs down its slope to the surrounding soil.

Nine: Mulch the tree's root zone.

Blanket the planting area with two to four inches of biodegradable mulch, but leave the area within one or two inches of the tree trunk bare of mulch.

("Okay I got it. Jump me to step ten.")

(Take me back to the list of ten steps.)


Mulch acts as a blanket to hold moisture, shield roots from temperature extremes, and reduce competition from grass and weeds. Research has shown that fine roots, those responsible for most of the water uptake in trees, can be fifteen times more numerous under mulch than in bare soil, and trees that are mulched may have twice the leaf density of those in beds without mulch.


Mulch, misconception:

Don't believe that: "If some mulch is good, a lot is better."

Volcano mulching is a killer. Mulch deeper than four inches may reduce oxygen and moisture in the soil, stressing and killing roots. Mulch that rests against the tree trunk, like excess soil, causes the bark to decay and eventually kills the tree.

Ten: Follow up with water for a full year.

Water whenever the soil in the root ball or the surrounding soil feels warm and dry. Continue watering into the fall and resume watering the next spring as soon as buds swell on trees in the area.

In one good growing season, roots can reach out to cover an area nine times as large as the original root ball. From that area the tree can draw water to grow for two weeks, a great improvement over the two day supply it had in the original root ball.

(Take me back to the list of ten steps.)


Follow up with water, misconception:

Don't believe that: "It's enough to water once a week."

Root balls filled with fine roots dry out far more quickly than garden soil. Container-grown root masses dry even more rapidly than B&B plants. For several weeks after planting, container grown plants may need water every day and B&B plants every two to three days. You decide when to water by feeling the soil in the original root ball.


One last misconception:

Don't believe that, "Trees should be pruned at planting time."

It was once standard to prune back hard at planting time to 'bring the tree's top into balance with the roots.' The 1961 Better Homes and Gardens New Garden Book prescribed "...in addition to pruning out broken and damaged branches, prune out 1/3 of all top growth." This has been proven to be both unnecessary and harmful.

Unnecessary, because for a field-grown, B&B tree there is no way short of killing the tree to reduce its top as much as its roots were cut. Field grown trees routinely leave 90% of their root system in the field! As for a container grown plant, we know that if we can keep its root system moist it may "take" without losing a single leaf.

 Some trees do lose limbs or leaves after planting, but studies have shown we cannot predict which portions will be lost. So prune sparingly at planting time, just to remove broken or damaged branches. Then wait for the tree to show you what, if anything, it must lose. Begin any other pruning only after the tree has grown on site for a full year.

 (Take me back to the list of ten steps.)


Where are the all tree-planting photos and diagrams?

Sorry! See really needs images, below. We will add more illustrations and merge this page with other tree planting basics as we continue to post articles from our archives. (As we type this, it's our second update.) Until then please refer to articles on this topic that we've illustrated and alread made available:

  • Our magazine Trees, available on our Market. Three articles cover tree planting basics, deciding what size tree to buy, and planting-related issues from mulching to staking and watering.
  • What's Coming Up issue #33 in which planting a tree inTreePlanting2561.jpg memory of our dear friend, arborist Dan Kurkowski, very appropriately yielded the best all-in-one photo of proper tree planting ever.
  • Or, forgive us, the text-only article above.


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