by Andrea Laine, Extension Master Gardener Volunteer
I used to call myself a flower gardener, but nowadays I feel more like a soil gardener. I credit the master gardener training program for my transformation. I was blissfully ignorant before I learned how important soil is to gardening success. Well, perhaps not blissfully, but ignorant nonetheless. I am now convinced that if there is a silver bullet to successful gardening, creating great soil is a strong contender.
My transformation began with a soil test in fall 2014. A soil test chemically measures soil elements essential to plant nutrition, including phosphorus and potassium, and makes recommendations of lime and/or fertilizer. The test also measures the soil pH.
Soil Report
When you have your soil tested, you receive a report that details what amendments you need to make in order to satisfy the types of plants you intend to grow in the area from which you took the sample. I sampled an 800 square-foot area along the north border of my property that is already home to four mature trees, three rhododendron, two camellias and one Japanese holly. For several years, the area has been mulched annually with pine straw. I plan to add more rhododendron, camellia sasanqua and viburnum shrubs and perennials to this shady border. Thus, I had the soil tested for Crop 1 – Azalea/Camellia and Crop 2- Mountain Laurel/Rhododendron.
The optimum pH range for azalea and rhododendron is 4.7 to 5.3. The soil report showed 5.7, which means my soil was not acidic enough for the garden I wanted to grow. Acid-loving plants may not grow or flower well in higher pH soils. And, indeed, the existing rhododendrons and camellias had hardly flowered at all. Not being in tune with my soil and its needs, I had guessed too much shade or too much heat was to blame, conditions that were largely beyond my control.
My soil was also deficient in phosphorus (P) and potassium (K). The agronomist’s report recommended 16 pounds of an acid-forming 5-10-10 fertilizer.
Amending Soil
The following spring I set out to make things right. First I picked up bushels of pinecones and raked away all the pine straw. I cultivated the soil by hand using a pitch fork to overturn it as deep as I was able, which was just two to four inches suggesting the soil had become compacted. (I was not surprised; it had not been turned over in at least 15 years.) Along the way I removed rocks of all sizes and encountered many roots. It was physically hard work. I consulted a few landscapers about doing the work for me, but none were interested. Then the hot summer months arrived and I lost interest in working outdoors.
In October 2015 the camellias, which had a few blooms each in recent years, burst forth with a plethora of pale pink, fragrant blooms. Up to this point, the only change I had made was turning over the soil surrounding these shrubs. What a difference it made! (Sadly, I do not have a photo.)
Ideally, soil is composed of 50% solid materials (45% mineral particles and 5% organic matter, roots, humus, organisms), 25% water and 25% air. Roots grow best in soil with a balance of moisture, air and mineral particles. My camellias’ roots may have been starved of air or moisture.
I resumed my DIY project with renewed enthusiasm. I laid down a couple inches of composted wood chips in the area around the six existing shrubs and gently worked it into the soil. The chips were made from maple trees felled by an ice storm in winter 2013. (I did not put down pine straw in 2015 or 2016.) In March 2016, a three-inch commercial mulch of pine bark fines and compost in a 50/50 mix was applied to the area.
Rewards
In April, the garden rewarded me with vibrantly beautiful spring blooms. I counted more than 30 flower clusters on just one rhododendron. New shoots are also growing from the base of the trunk.
Absent a soil report, I doubt I would have gone to the trouble I did to improve my soil. And I am not finished yet. Organic matter is dynamic – bacteria and microorganisms break it down over time—so it must be replenished periodically. It’s been almost two years since I had the soil tested. Given the changes I have observed, I will have the soil tested this summer and again a few months after applying fertilizer. I will not add new shrubs to the area until I have successfully lowered the soil pH, something I cannot know without a soil test.
Do as I Say, Not as I Do
In an ideal world, the best way to have renovated this particular landscape bed would have been to follow the steps below. I set out to do things this way, but limits on my time, strength/energy, and money caused me to follow a somewhat alternate route as I described above.
The ideal process would have been completed in one season:
- Clear the debris – pinecones, twigs, leaves and old mulch.
- Cultivate deeply to loosen compacted soil. Compacted soil can prevent water from reaching a plant’s root system.
- Apply a three to six-inch layer of organic material (compost) and incorporate it.
- Apply the fertilizer recommended by the soil report and incorporate it.
- Another way to increase soil acidity is by applying elemental sulfur. I chose not to do this because the turnaround is slow and sulfur can harm existing plants as well as people.
- Wait a season or two and then retest the soil.
Although I had to cut some corners, I learned that a little TLC of garden soil pays big dividends. Now I know that being a soil gardener can lead to an outstanding flower garden.
Additional Resources
Understanding the soil report:
http://www.ncagr.gov/agronomi/pdffiles/usoilHG.pdf
Learn more about incorporating organic matter to amend soil: http://content.ces.ncsu.edu/extension-gardener-handbook/1-soils-and-plant-nutrients#section_heading_7239
Educational videos about soils: http://forces.si.edu/soils/