Publications (Paul's Blog)

June 21, 2010

FIRST YOU DIG A HOLE

Filed under: Uncategorized — Paul Dowlearn @ 9:32 pm

  I tell my young landscaping apprentices more often than they would like to hear that there is technique to everything. Even something as straightforward as digging a hole involves having some technical knowledge. There are a lot of folks planting trees and shrubs right now (or at least there should be). I thought it may help some to share with you some of the same techniques we use in our landscaping operation.

  The hole itself should be dug to the exact depth of the root mass. This has changed since I was a young apprentice. Back then we were intent on digging deep (sometimes 4 feet or deeper) and planting trees below grade thinking that the softer soil would encourage deeper rooting plus cause water to puddle around the trunk allowing more to soak in. Research since has proven that the deeper roots on any tree function as anchors as well as water and mineral conduits. Making the natural subsoil available instead of over digging the hole benefits the young tree by allowing it to anchor in firmly and quickly. When you consider that trees in Nature have always been able to penetrate the local sub soils regardless of how impenetrable they seem, this makes perfect sense. Now I wish I could go back in time and not have to dig all those deeper holes I dug.

  The width of your hole should be at least a foot wider than your root mass diameter. Wider is better. Again research has shown us that the feeder roots are generally concentrated in the top foot of soil. I never talked to a single client who did not want fast growth on a newly planted tree. The wider you dig and loosen the soil, the faster the shallow feeder roots can establish. You can even do this after you have planted by using a rototiller of digging fork and work out away from the trunk and root zone. How wide you loosen the soil around your tree is up to you. Remember that wider is better. Add an inch or so of compost to this perimeter for best results.

  Before you lower the root mass into the hole make certain the hole is flat at the bottom. All plant containers are flat on the bottom and you want good root to soil contact. No air pockets. A large enough air pocket can kill.

   Once the tree is in the hole check again to make certain the top of the root mass is even with or slightly above the existing grade. Most trees do not benefit from being planted below grade. The exception to this would be water lovers like bald cypress, American elm, or willow.

  Backfill with your native soil, breaking up any large clods as you go. Do not add any soil amendments to the backfill. Once again, this is a complete reversal of what I was taught years ago, but the fact is that your selected tree must be capable of growing in your existing soil sooner or later. Adding peat moss, potting soils, compost, or manures to the backfill creates what I call an “underground pot.”  This does not encourage the feeder roots to fan out naturally in search of nutrients but instead encourages them to stay within the rich soil you provided in the hole. Also since this loose mixture will drain differently than the surrounding soil it can contribute to death by drowning. We call this the “bathtub effect.”

  As you backfill, water in slowly to settle the soil. Do not tamp or compact the soil.  You should take your excess soil and form a berm around the root zone. This will help concentrate water on the roots for that critical first summer. Next you should apply an inch of compost over the root zone then top this off with a nice layer of mulch. Chopped up tree leaves make the best mulch but shredded hardwood will do in a pinch.

  You’ll notice I did not mention any root stimulators, fertilizers, and such. The tree will get what it needs from the soil and compost plus decomposing mulch. All you really need is to water when dry the few years while the tree becomes established. However, there is a new technology we like to use.

  We now sell a mixture of beneficial fungi and bacteria to mix into the upper portion of the backfill. Mycorrhizal fungi and rhizobacteria are microbes that really do stimulate roots and live symbiotically within the rhizosphere (root zone) and inside the roots themselves. Although these critters do exist naturally in the soil and compost, this is a way to make certain the proper arrays of microbes are in contact with the roots right off the bat. The tree gets the benefit of increased root hairs, better absorption of minerals, and disease protection. Another great benefit is these living creatures increase with the root system as it grows therefore one application done correctly can last for the entire life of the tree.

  Large shrubs that are planted out in the lawn are given the same treatment as trees. Shrub beds that are planted en masse require different tactics. When planting shrub and perennial beds we want to eradicate lawn grasses and improve the entire area.

  The first step is to physically remove existing grass. We find the most expedient way is to simply dig it out, roots and all. This should be done with diligence, especially in the case of Bermuda grass. Any portion of the stolons (above ground runners) or rhizomes (below ground runners) are capable of regenerating quickly to spoil your new plantings and make further attempts at eradication even more difficult. Some folks resort to solarization with plastic which is fine if you have the time or smothering by layering newspaper, or they install a landscape fabric or (worst case) resort to herbicides. The digging method works just as well if not better than these alternatives and is much quicker.

  Next we will add soil to the entire area. We use a mixture of fill sand (bulk top soils will nearly always contain weed seed, Bermuda, Johnson grass, or nut grass) mixed with compost. Mix one part compost to two parts sandy loam for a good rich mix or use less compost for true dry country plants. Always crown the beds to rise above the surrounding grade as most ornamental shrubs will benefit from well drained soils. Once again, rather than going deep to attempt to improve subsoil we have found it best to simply dig (or rototill) down 6 or 8” then raise the bed up with our rich mixture. You may raise your bed anywhere from several inches to several feet to suit any slope or visual angle.

  This raised bed technique works especially well on problematic soils such as hardpan clay, caliche, or stone. It is so much easier to build up rather than dig down through hard materials. Scooping out hardpan and replacing with amended soil also tends to create the bathtub effect the same as it does with tree holes. Break up the existing topsoil (if there is any) and build up rather than down.

  The only real pitfall we’ve run into using these raised beds is you can create runoff problems if you aren’t careful. Raised beds cause more runoff and at the same time can act as a dam to restrict water flow possibly creating a flooding problem. Of course this can work to your advantage with a little planning. My mother used to construct her shrub beds where the hose could be laid on the high end and the water would naturally flow to the opposite end making it convenient to flood irrigate without having to move the hose around. Astute landscapers in west Texas use a system of swales and berms to trap runoff and make good use of whatever rain may fall. Be observant of runoff and you can design shrub beds that work for you.

  First you dig a hole. Remember to put soil amendments on top rather than deep underground. Plant at or above existing grade. Don’t forget that it is much easier to build up rather than dig down. Rely on compost to fertilize and don’t forget to mulch. The result will be increased livability, faster establishment, and less long term maintenance. Not to mention the fact that these methods are also much easier on the gardener too. Enjoy!!!

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