It's time to get your garden going and soil is the place to start. Healthy soil leads to healthy plants that resist pests and diseases without pesticides. From compost to hydrogels, mycorrhizal fungi to eggshells, we learned what's safe and healthy and what's not from Metro natural gardening expert Carl Grimm.
What is a soil amendment?
Almost anything you mix into your soil – that is not exclusively a fertilizer – is an amendment.
When in doubt, get a soil test.
If your soil is already dark, crumbly, earthy-smelling and full of worms, or if your plants seem happy and healthy, your soil may not need amendments. But most home gardens could use a little boost, especially for veggies, annuals and new plantings. A test can help. Oregon State University Master Gardeners can help you find a testing service.
Compost is king
Compost improves soil structure – increasing drainage in heavy clay and water holding capacity in sandy soil. It reduces polluted runoff into our rivers and streams. It’s also teaming with beneficial organisms that make free fertilizer from air, rocks and decomposing plants. You can make your own compost from yard trimmings and food wastes, or buy it from the nursery.
Other amendments help supplement compost
• Pumice and quarter-ten gravel are great for improving drainage. Both are locally produced and are better than perlite which requires a lot of energy to make, or vermiculite, which may have asbestos contamination.
• Aerated compost tea, available at some nurseries, or homemade compost extract add soil microbes without as much heavy lifting. Results depend on the quality of the compost the extract is made from.
• Miccorhyzal fungi is now sold in many nurseries and may be used to introduce beneficial microbes to your soil. The microscopic fungi attach themselves to plants’ roots, protecting and extending the root system.
• Polyacrylamide hydrogels are toxic and unnecessary. They contain small amounts of a nerve toxin called acrylamide. Hydrogels are often found in potting mixes, so look for ones without them or ones with yucca or cornstarch-based hydrogels.
• Avoid the peat moss/coir controversy. Peat moss is a non-renewable resource harvested from sensitive bog ecosystems, and its popular “greener” alternative is coir, a coconut husk fiber shipped from far away. Both are nice brown, fluffy drainage-makers, but good compost is still king for amending garden soil.
Alfalfa meal is awesome
Alfalfa pellets are an excellent fertilizer-amendment that gives a boost to veggie beds and new plantings. Soybean meal and linseed meal are also good choices.
• You may want to avoid feather meal. Studies have shown antibiotics and arsenic contamination. But other meat byproducts like blood meal and bone meal are effective organic fertilizers.
Eggshells are an easy and economical calcium source, but basic lime is good, too. Lime can also be used if your soil is overly acidic.
Micronutrients are no small thing
Cascade Minerals, Azomite®, kelp meal, greensand and Naomi’s Mineral Mix are all fantastic sources for a wide array of trace minerals that help plants grow. Add a little every year or two to veggie beds.
Got soil amendment questions? Grow Smart Grow Safe has answers. Get your free copy by calling Metro at 503-234-3000 or visiting oregonmetro.gov/garden