How to Use Fertilizers-Rock Dust

As your garden grows year after year, the minerals that are native to your soil are used up and need to be replenished. Rock dusts are a natural, easy to use soil amendment for this! Using rock dust in your garden is a great way to add trace minerals and micronutrients to your soil. Rock dust is also sometimes called rock flour, rock minerals, rock powder, stone dust, soil remineralizer, and mineral fines. It can be made of any kind of mined rock that is ground to a powder.

What Does Rock Dust Add to My Soil

  • Adds trace minerals and micronutrients
  • Increases the Cation Exchange Capacity, or CEC, of your soil.
  • Feeds the beneficial microbes that live in your soil.

Not All Rock Dusts Are Alike–How to Choose Which One to Use

All rock dusts provide minerals for your soil, but different rocks are made up of different minerals. Getting a complete soil analysis done on your soil can help you determine which type of rock dust is best for your needs. Rock dusts cannot burn your plants’ roots, so there is no risk of over application. However, applying more than the label’s directions indicate will not provide any additional benefit to your soil or plants. The minerals it provides are only needed in small amounts, and there is a natural limit on how much can be utilized at once and how fast it can be used up.
https://cdn.shopify.com/s/files/1/0061/1391/9089/files/Rock-Dust-Comparison.jpg?14810There are three primary sources for rock dust: Glacial Rock Dust, Basalt Rock Dust, and Azomite. Let’s take a closer look at what their differences are.

Glacial Rock Dust

Glacial Rock Dust as the name says, is made from rocks deposited by glacial action. When glaciers move across the landscape, they pick up rocks and carry them for tens or even hundreds of miles. Glaciers that spill out from a mountain range onto a large flat area are called piedmont glaciers; when they melt they leave behind a moraine, which is basically a field of rocks that the glacier had carried along. This mixed pile of rocks is where glacial rock dust comes from.
  • Made of a wide variety of rocks, it contains a complex blend of minerals.
  • It is particularly good for adding calcium, iron, magnesium, and potassium.
  • It also contains some manganese, cobalt, silicon, and small amounts of other minerals as well.
  • Top dress it in your garden, potted plants, or raised beds.
  • Use 2 1/2 lbs per 100 square feet of garden, or 1 Tbsp per gallon of soil or potting mix.
  • Sprinkle around the plants and gently rake it into the surface. Reapply as needed, or up to once a month.

Basalt Rock Dust

Basalt Rock Dust is made of the volcanic rock called basalt. It is actually a byproduct of mining basalt for other purposes, such as landscaping decorative rocks, construction, and industrial uses. When the rocks are crushed to the size needed for those purposes, some of it is rendered into powder in the process. This is collected and sold as rock dust for gardening. Because of this, of the three main types rock dusts, basalt can be considered the most environmentally friendly. Some gardeners prefer basalt over glacial rock or azomite because of the risk of heavy metal contamination in those other products. Although our Azomite and Glacial Rock Dust have been tested and are safe to use, this may be a factor in your decision of which rock dust to choose.
  • Basalt rock dust contains a more limited variety of minerals than the others.
  • Excellent source for calcium, magnesium, iron, manganese, silicon, cobalt, zinc, boron, and aluminum.
  • Top dress 10 lbs per 100 square feet of garden before planting, and another 5 lbs mid-season.
  • For potted plants, mix in 1 cup per cubic foot of potting soil before planting, or top dress with 1 tsp per inch of pot diameter.
  • For trees or shrubs, use 1 cup per 1 inch of trunk diameter, spread over the root zone. Rake in and water thoroughly.
  • For lawns, use 50 lbs per 1000 square feet, or if you’ve aerated your lawn first use half as much.

Azomite

Azomite is a unique type of rock that comes from only one mine in central Utah. Azomite is an acronym of the phrase “A to Z Of Minerals” followed by –ite: the common ending for a rock name. Azomite was formed when a volcano spewed tons of ash into a nearby seabed millions of years ago. The water dried up and the resulting ash-and-marine muck turned into rock. In geology terms, Azomite is called “hydrated sodium calcium aluminosilicate.”
  • Contains the widest range of minerals of all the rock dusts.
  • Good for magnesium, calcium, potassium and silicon, and also provides about 70 additional trace minerals.
  • Apply 10 lbs per 100 square feet of garden, or 1 lb per 25 root feet by top dressing or watering it in.
  • For potted plants, use 1/2 teaspoon per inch of pot diameter mixed into the soil before planting, and 1 tsp every 3 months while the plant is growing.
  • For trees, use 1 to 5 lbs each, depending on the tree size. For shrubs, grapes, and roses, use 1/2 to 1 lb per plant. Spread it around the root zone and rake it in.
  • For new lawns, use 5 lb per 1000 square feet, and for established lawns use 3 lb. Apply once per year in spring or fall, broadcast evenly and water it in.
When you’re planning what to feed your garden this year, don’t forget about adding trace minerals. Choose a rock dust and grow organic for life!

6 comments

  • David, you can mix it into the soil and water it in. It is soluble so it will be fine to add it after you have planted.

    Suzanne
  • I’ve been searching for solid information on rock dust. This is great info. Thank you for sharing!

    Tina Colwell
  • Heavy metal contamination in azomite and glacial rock dust would it be harmful to fruit trees?

    Carol
  • This info is so great! Thank you much!

    Elise
  • If I forgot to mix Azomite into my container mix, can I just scratch it into the top few inches now that the seedlings have sprouted and are about 1.5” or should I skip it? I’m growing beets.

    David
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