The One Piece of Gardening Advice I Don’t Agree With

October 3rd, 2023

   I’m generally a believer in following what research reveals, especially if it’s solid research and backed up by multiple sources.

Research notwithstanding, I’m still a believer in working compost into my soil before planting.

   But the one bit of gardening advice that I still just can’t buy is the one about not improving the soil before planting.

   This fairly widespread guidance comes from findings that plant roots can rot from a so-called “bathtub effect” when the soil is improved.

   The premise goes that when you give a new plant a generous helping of compost or similar organic amendment in the backfill mix, water will drain well through it. But when the water hits the wall of undug, compacted soil under and around it, it can’t drain as fast.

   That’s when water can back up in the planting hole, where it fills the small air pockets in the soil, suffocating and rotting the plant to death.

   The experts arrived at a rule of thumb that planters should never mix more than a 10-percent improvement into existing soil (i.e. add no more than one bucket of compost to nine buckets of dug-up, loosened native soil).

   I don’t question that logic and believe that’s definitely one of the many ways to kill a plant.

   The disagreement I have is that I’ve seen way, way more plants struggle and die because roots can’t penetrate the soil that gardeners haven’t improved.

   The basic problem is that most of us here are trying to garden in heavy clay, packed shale, and worst of all, subsoil – that farther-down, compacted medium that was on its way to becoming rock before earth-moving equipment dug it up in the home-construction process.

   I’ve seen first-hand how gardeners are set up for failure as a result of how building sites are prepared.

   What usually (or at least often) happens is that the earth-moving equipment first scrapes off the real topsoil, selling or moving much of it. In the development built just below me years ago, I saw truck after truck, day after day, leaving the site filled with some fairly decent soil.

A typical construction pile of “soil” that’s to be used for finish-grading.

   Then, whatever topsoil is left – along with the subsoil that needs to be moved to craft the specified grades – is piled up out of the way on site.

   As homes are built, loaders go to the pile to “finish-grade” each lot. That often means just a few inches of the piled “soil” goes on a layer over top of the graded subsoil.

   While those few inches might be enough to grow grass and support young plants, what happens in the long run is that trees, shrubs, evergreens, and even perennials can’t penetrate the layer below.

   Within a few years, growth is stunted, plants are struggling, and some of them start to die when the limited roots can no longer supply enough moisture to the expanding top growth. Hot, dry spells are particular threats.

   Gardeners usually blame themselves at that point – for not watering enough, for not fertilizing enough, for some unknown other botch, or the general “I have a black thumb.” (Read my post on why I don’t think there’s any such thing as an inherent black thumb in gardening.)

   I’d seen enough of this plant torture over the years that I began to improve all of my lousy soil with about 20 to 25 percent amendments. I usually make that improvement over a whole bed before planting – first digging about a foot deep, then raking a two- to three-inch layer of compost over the bed, then thoroughly incorporating the compost into the loosened existing soil.

   Even when planting a single tree instead of a bed, I loosen at least three times as wide as the rootball and improve with two five-gallon buckets of compost.

   Yes, that’s a lot of work and a lot of compost (which is why the best thing you can do as a beginning gardener is build yourself a couple of compost bins). But the results have been well worth it.

   I’ve lost way fewer plants than an average homeowner and have easily saved more money in not replacing dead plants than I’ve shelled out in sweat equity.

   I also started telling my design clients to skip the no-soil-improve advice and go ahead and give their soil a healthy dose of air-supplying compost. The feedback I got from so many of them was that they were surprised at how well their plantings grew – noticeably better than their past experience.

This dwarf arborvitae ‘Whipcord’ has gone nowhere in three years, so it’s about to be dug and invigorated with a bucket of compost.

   What really nailed it down for me was when I started digging up struggling plants and replanting them in improved soil. Most of the time, this involved either plants that were planted into unimproved soil or ones planted in soil that was meagerly improved. This included plants that went in before I started bypassing the no-improve advice and ones planted when I was running short of compost.

   In almost every occasion, these plants perked up almost immediately and started sending out new shoots. It’s almost as if they were saying, “Thank you for loosening that noose around my roots!”

(Read more on how to help struggling plants in my post on “Failure to Thrive.”)

   The bottom line for me is that in this case, first-hand experience is going to win out over the research recommendation.

   That research probably makes good sense where gardeners are starting out with actual and decent soil, not the clay/shale/subsoil death trap that our subdivision yards have.

   And maybe it makes sense in places where the bad-drainage threat outweighs the bad-soil threat.

   At least in my yard, though, the plant lesson is, “Give me compost or give me death.”