Fielding Questions: Potting soil can be reused for several years

Q: I have some potting soil from last year that was never used, and it's still in the original bags. Is this just as effective for use this year? What are the guidelines for using soil from year to year, both new and used? I recently read that it...

We are part of The Trust Project.

Q: I have some potting soil from last year that was never used, and it's still in the original bags. Is this just as effective for use this year? What are the guidelines for using soil from year to year, both new and used? I recently read that it's OK to reuse soil for up to three years if you add the material that's in Miracle-Gro. - Mary Przymus, Fargo

A: Both unopened and partially used bags of potting mixes remain usable for years. They should be stored dry to keep the little beads of slow-release fertilizer that are present in many mixes from dissolving. Bags stored on wet ground can absorb moisture through the tiny air pores in soil packages, so store bags with adequate air circulation.

Large outdoor planters and containers require large quantities of potting mix, and yes, the same mix can be reused from year to year. Begin with a good-quality mix like Miracle-Gro Potting Mix or a mix recommended by locally owned garden centers. Each spring before planting, remove about one-fourth to one-third of the old mix. Replace with fresh and stir well. The old discarded material can be added to flowerbeds or garden.

The product to add, as you mention, are the little beads of slow-release fertilizer to replenish those that have been depleted from the old mix. A commonly available brand is Osmocote. The directions indicate how much to add for different diameter pots.

My wife, Mary, and I have reused the same soil in containers for five or six years and they're still going strong, with the addition of a little new each spring plus adding Osmocote granules.


Q: I covered newly planted tulips, daffodils, poppies and irises last fall with about a foot of soybean straw. When should I start uncovering them since it looks like it will be an early spring? - Shirley Herberg, Gardner, N.D.

A: Although the recent weather has been very mild, we could still get weeks of very cold temperatures. It's best to keep the straw in place for as long as possible to keep the soil frozen and delay the awakening of the bulbs and perennials.

If the straw is removed too early and the soil thaws, there is danger that the plants will begin to grow unseasonably early. Then if we get a spell of severely cold weather, the newly-growing plants could be injured or killed. It is much safer to keep them dormant until spring stabilizes and we quit swinging back and forth between winter and spring.

Check the plants frequently under the straw. If they begin growing, rake the straw aside, but be prepared to cover the plants with the straw again if winter returns. It's much safer to keep the plants covered and dormant until late March or early April, and then remove the protective mulch.

Q: I planted a few pots of Miscanthus flame grass in my backyard. The plants survived, and most yielded the beautiful plumes that are so pretty in the wind. I tried in vain to plant some of the seed from these, and although I tried every possible technique I could find, nothing would sprout. Have you had any experience with my problem? - R.A. Hewitt, Red Wing, Minn.

A: The botanical genus Miscanthus is a large group of grasses that grow 3 to 8 feet tall. Some members spread vigorously by underground rhizomes; others form a rounded clump that slowly increases in diameter. Some types lack hardiness; others survive our winters quite well.

Named cultivars have been chosen for their ornamental foliage, decorative flowering plumes and attractive growth habit. These named selections of Miscanthus reportedly produce little or no viable seed, which probably explains why the seed you collected has failed to sprout. Miscanthus cultivars are propagated by dividing existing clumps, instead of by seed.

You might be lucky the seed didn't grow. If tame varieties happen to cross with invasive types, viable seed can be produced that might result in the spread of very invasive seedlings. Homeowners are advised to monitor Miscanthus plantings, remove any little seedlings that ever grow, and don't propagate them by seed.


Named varieties of Miscanthus that are considered good choices for our region include Autumn Red Flame, Amur Silver, Malepartus and Silberfeder Silver Feather Grass.

Foliage of ornamental grasses should be left intact during winter, instead of cutting back in fall. Winter survival increases, and the dried foliage and flower plumes add winter interest to the landscape. Cut foliage back to slightly above ground level in early spring before new grass spears emerge.

If you have a gardening or lawn care question, email Don Kinzler at . All questions will be answered, and those with broad appeal may be published, so please include your name, city and state for appropriate advice.

Related Topics: GARDENING
What To Read Next