Amendments make soil better for growing plants

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Soil is more than just a place holder for plants. Soil holds moisture and nutrients plants need to grow, and soil structure determines how easily roots can spread out and take up nutrients. Garden soil can become compacted and depleted of necessary nutrients over time and must be replenished.

Most plants like well-drained soil that holds some water, is easy to work, and contains a healthy balance of nutrients. Heavy clay soil often holds too much water and is difficult for roots to break through. Sandy soils drain too quickly, wash out nutrients, and make it hard for plants to obtain the water they need.

Soil structure and nutrients can be improved by adding amendments. To determine what type of soil you have, hold a slightly damp amount in your hand and squeeze. If the soil forms a tight ball that must be pulled apart, you have a high amount of clay. If the soil is gritty and doesn’t hold together, your soil is sandy.

Loam, an in-between version, is the most desirable soil for plants to grow and for gardeners to work. If you don’t have loamy soil, amendments can be added to improve the structure and aid plant growth.

Compost is gardener’s black gold. It is made of organic matter (once-living material such as leaves, grass, etc.) that has decomposed. Compost is great for both sandy and clay soils, improving water retention, aeration, and the ability of the soil to hold nutrients. Composted manure is animal waste that has been thoroughly decomposed and it is a great amendment and fertilizer.

Tonkadale offers several types of organic compost and fertilizer:

  • Wiggle Worm Organic Earthworm Castings (yes, it’s worm waste, and it’s wonderful!).
  • Coop Poop (from chickens).
  • BuffaLoam.

Espoma Peat Moss is also a great amendment to prevent or improve compaction.

Inorganic amendments (not once alive or from something alive) can also improve soil structure. Vermiculite and Perlite (those little white pieces in bagged potting mix) both improve aeration and water retention, but they are not exactly the same. Vermiculite holds more water and is best for amending the soil of plants that crave water, such as irises. Perlite dries out more quickly and is better for plants that like it a little drier, such as cactus and succulents. Garden Gypsum is another good option to loosen clay soils.

Adding sand to heavy clay soils is not recommended. A small amount does no good and can actually increase compaction. The large amount required is very labor intensive to work into the soil. Worst of all, there is the risk of creating concrete rather than a nice workable garden.

With all soil amendments, be sure to follow the recommended amount for application. Apply amendment to the soil and work in by hand or rototilling.

The type of soil used in container gardening is also very important. Using soil from the ground for containers is not a good idea because it generally does not have adequate structure and nutrients for container-grown plants. A good potting soil for containers must be able to retain moisture but also have very good drainage. TonkaTerra, Tonkadale’s own specially formulated potting mix, contains weedless organic compost, sphagnum peat moss, perlite, fine composted bark, and natural nutrients.

The best way to know what kind of soil you have and what your soil needs is to have a soil test performed. The University of Minnesota performs basic tests for a small fee. For more information visit

For more information, check out these soil-building tips at Bonnie Plants:

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