Is it safe to use cinder blocks in raised beds?

    Listen 00:52:57

    Are there cinders in cinder blocks? Mike McGrath, host of You Bet Your Garden, will investigate whether the big blocks are safe to use around people and plants. Plus Mike speaks with author Lynn Steiner about native plants that will add beauty and attract pollinators to your landscape.


    Questions of the Week:

    “A couple of years ago I started re-reading my old ORGANIC GARDENING magazines from when you were the Editor (I kept them all!), which led to me finding your podcasts and I’ve been listening ever since. Now I have a question: Are cinder blocks safe to use to make raised beds? My daughter would like to use them for this purpose but the information pro and con on the internet is confusing and unconvincing. Is there really a risk of the substances used in making the blocks leaching into a raised bed? (In the Pacific Northwest we get a lot of precipitation, which can cause a lot of leaching). I told her that I would trust your opinion. Thank you for continuing to help keep our world safe. P.S. I was one of those subscribers who had to fight to get the issue with the infamous comic book cover away from my kids! “

    — Wanda in Scappoose Oregon (20 miles north of Portland)

    Learn about using cinder blocks in your garden »

    Highlights from show for July 2, 2016:

    Reigning in overgrown landscaping

    Nicole from Brooklyn, New York recently purchased a hundred-year-old farmhouse as a weekend country home in New Hope, Pennsylvania. Left to its own devises over the past few years, the yard has become overgrown with a beautiful, but wild, landscape. Nicole wonders what is the best way for her and her husband to tackle the yard, which includes an in-grown garden, fruit trees, and bushes of all varieties. “I think you need a hired man. You can’t keep a summer garden, with vegetables and things like that, going with only two days a week,” Mike tells her. “You pretty much need somebody there every day doing a walk through.” Not all plants will need daily care; cane fruits and berries do well on their own. As for the upkeep of their fruit trees, a hired landscaper would provide proper care during the week while the couple works in Brooklyn. “If you bought this house for a weekend retreat, you have to keep that mindset,” Mike advises. “You are not there to work, and if it needs to be done, you pick up the phone and have somebody come and do it.”

    Strawberry tips

    Frank from Saltville, Virginia is having trouble with his strawberries. Although the plants are blooming nicely, they fail to produce berries. With the plants filling a raised bed about 80 feet long and 2 feet wide, it is disappointing for Frank to harvest only a gallon this season. Mike asks about the composition of those raised beds, which Frank believes to be only the local dirt and a composted top soil, which he tilled into the dirt. “In the future, any time you get a nice load of compost, don’t till the soil,” Mike says. “When you till the soil you release nutrients and you expose weed seeds to the trigger for germination.” In a big strawberry bed, weeds are your worst enemy. Mike tells Frank that if he wants to buck up any nutrients for flowering, he should look into purchasing rock phosphate. “That’s the nutrient that encourages plants to put on a lot of bloom and allows those flowers to become fruits,” Mike says. Rock phosphate is the most natural form of phosphate and a little bit goes a long way. For Frank, this means a cupful per 20 feet on his row of strawberries. This process only needs to be done every three to five years. Mike recommends that Frank try a new line of liquid fertilizers by Espoma, one of which is called “Bloom!” Mike also advises Frank to purchase a bag of rock phosphate and dust it around the plants in preparation for next year’s bloom.


    Featured interview: Lynn Steiner

    Mike speaks with Lynn Steiner, author of Grow Native: Bringing Natural Beauty to Your Garden. Mike and Lynn help a caller figure out what native plants to plant on top of a septic system. Lynn gives some great species of plant that would be an excellent way to plant it and forget it. Service berries are a favorite of her and are most underutilized native plant. Some of the positive aspects include an early spring bloom, one of the first genera to set fruit in the summer and humans can actually eat service berries . Lynn says in 30 years of gardening she’s learned a lot. “Gardening isn’t always such a green hobby and I try very hard to become what I call a responsible gardener.”


    Landscaping around septic mounds

    Kristin from Franklinville, New Jersey received advice from both Lynn and Mike about what native plants to feature in her new backyard, currently an open space sprinkled with grass seed and bordered by forest. The only presence in the clearing is a septic mound covering recently installed plumbing. Lynn warns about gardening on an area covering a septic system, emphasizing the importance of planting something shallow rooted. “Don’t dig down too deeply in this area and don’t use a Roto tiller,” she says. “Wear gloves, the soil can have some contaminants.” She advises to plant with things that can be left untended. Fiber rooted grasses such as little bluestem and prairie dropseed would do well, along with herbaceous plants such as nodding wild onion, native coreopsis, and purple coneflower. Once you get away from the septic area, then the “sky’s the limit.” Some of Lynn’s favorite plants include the long, tough blooms from anise hyssop, amsonia blue star, and butterfly milkweed, which always tops the list due to it’s attractiveness to monarch butterflies. Later in the season, asters flowers and sneezeweed look nice in a natural landscape. As Kristin’s yard nears the woodland, Lynn recommends things that can tolerate shade, such as maidenhair fern, wild ginger to cover the ground, bleeding hearts, and bowman’s root. “There are so many beautiful plants that give you a tapestry of foliage colors and textures,” Lynn says. As Kristin begins her journey gardening with native plants, Lynn recommends she visit Bowman’s Hill Wildflower Preserve and Mt. Cuba Center, two excellent local resources in eastern Pennsylvania and Delaware.


    Growing gardenias

    Sharon from Byhalia, Mississippi is struggling to grow her gardenias due to the excessive shade they receive from her front porch’s overhang. She asks Mike if she can dig them up and move them into the sun at this time of year. Mike admits that we’re probably into the worst two months to do so. Instead, he suggests Sharon wait until next spring, after all chance of frost is done. “If you do it now, the heat stress will absolutely kill them,” Mikes warns. To keep the plants safe in the winter months, Mike says to drive tall stakes into the ground around the plants and wrap burlap around them as high as the stakes go, creating a wind break and heat sink. This is the best way to protect the plants without harming them. “Don’t put anything directly onto the plants, they don’t need it and it can crush them,,” Mike says. Some winter damage to the top of the plant is inevitable. By waiting until spring and correctly shielding the plants from frost, Sharon should be able to safely relocate her gardenias next spring. “They won’t even know they were moved!” Mike says.


    Gardening under water restrictions

    Bill from Ortley Beach, New Jersey is moving to the central valley of California and has concerns about gardening in the dry heat with state water restrictions. Mike recommends the installation of a gray water system. As white water is what comes into your house, gray water is what leaves from things like the shower, sink, and washing machine. “All of that water can be diverted,” Mike says. After installed, the water waste will go into a holding tank. which funnels into drip irrigation lines. These lines then feed into the garden underneath the mulch to maintain the least amount of evaporation. Under this system the water will be applied to the plants at the time it leaves the house, when it is perfectly safe. “You should be able to keep a good size garden well watered,” Mike tells Bill. In addition, he’ll never actually have to go outside and water the plants, since they’re watered every time he takes a shower. “Try to avoid doing it in the heat of the day because the plants are closed up tight,” Mike advises. “You want to time that big water use to the morning or evening.”

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