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Linda Naeve, Reiman Gardens, (515) 294-2710,
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,

Sphagnum Peat Moss Improves Poor Soils

By Linda Naeve
Extension Coordinator
Reiman Gardens

Spring has finally arrived! You don't need to check the date on the calendar or the temperature on the thermometer to tell. You don't have to look for robins or blooming crocus. Simply drive past garden centers and discount stores where you will see tall piles of bagged mulch and soil amendments. This week's Reiman's Pick is part of that menagerie of products and the first thing to go into a garden in the spring - sphagnum peat moss.

Sphagnum peat moss is often confused with sphagnum moss. Sphagnum peat moss is the dead, mostly decomposed, material that accumulates in the lower levels of a sphagnum bog. It is the fine, dry, light brown material sold in compressed bales.

Sphagnum moss, on the other hand, is composed of the long, fibrous strands of a primitive plant. It grows on the top of a sphagnum bog. It is used in the floral industry to line wire baskets and is occasionally used as packing material around the roots of trees and shrubs when they are shipped bare root. Sphagnum moss also is used as a packing material for worms sold as bait. It absorbs and retains a large amount of water, just like a sponge. The top few inches of the live sphagnum moss are removed before the peat from the lower levels of the bog is harvested.

Sphagnum peat moss is a valuable organic soil amendment with many horticultural uses. It is probably the most convenient form of organic matter to apply to garden soil. It is often used in place of compost or stable manure because it is readily available and much easier to haul.

The ability of sphagnum peat moss to absorb large amounts of water (up to 20 times its weight) makes it a valuable amendment to light, sandy soils by increasing its water-holding capacity. It allows more air to enter tight soils and increases the rate of water infiltration in fine-textured clay soils.

With a pH around 4.0, sphagnum peat moss is a great soil amendment for acid-loving plants such as azaleas and blueberries. When planting acid-loving plants, mix sphagnum peat moss with soil at a 50/50 ratio in the planting hole and apply a 2-inch layer over the soil surface. The peat helps to lower the soil's pH, allowing the plants to absorb nutrients such as iron.

Garden soils will benefit from a 1-inch layer worked into the top four inches of soil. It also can be used as a top dressing on lawns. A 3.8-cubic foot compressed bale of sphagnum peat moss will cover about 90 square feet with a 1-inch layer.

Many potting soil mixes, including the soil-less mixes, are peat based. It keeps the mix loose and helps it retain nutrients.

Pots used for growing transplants are made of peat. When moistened, the roots of the seedlings grow through the pots so they can be planted, pot and all, directly into the garden, thereby reducing transplant shock. Eventually, the peat pot decomposes.

Sphagnum peat moss played a vital role in the early success and survival of the annual and perennial flowers at Reiman Gardens. Like many urban soils, the soil at Reiman Gardens was heavy clay and did not drain well. To keep the plants alive and prevent them from rotting due to heavy rainfall and poor drainage, a three-inch layer of sphagnum peat moss was worked into the flowerbeds the first summer. "It saved our plants the first year and improved the condition of the soil for future year," said Nick Howell, garden superintendent at Reiman. "It was an incredible remedy for our poorly drained soils."

To learn more about the Reiman Gardens at Iowa State University visit us on the Web at:


Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The picture's fullsize photo is 520K.

Caption: Peat was worked into the soil when this tulip bed was planted in the Margaret Penkhus Campanile Garden at Reiman Gardens. This garden will be bursting with blooms in late April.

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