Skip to main content

WCCO Radio "Smart Gardens" Q&A - September 6, 2014

Thanks for listening!

We aren't always able to answer everyone's texted questions on the air, so we try to post a few along with answers here in the Yard & Garden News blog. Remember that you can always visit the U of M Extension Garden website for loads of gardening resources.

Hope you join us and our host Denny Long every Saturday, 8-9am, on WCCO Smart Gardens and happy gardening!

20140714_123750.jpgQuestion: It looks like my Black-Eyed Susans have powdery mildew. Will they be OK next year and what can I do?

Answer: Powdery mildew is a common fungus in Minnesota landscapes that results in a white powdery covering over leaves. Usually damage is cosmetic and the plant recovers fine the next year. The best means of managing this pest is to (1) select resistant plants, (2) space plants properly to ensure air circulation, (3) water at the base of the plant (vs. overhead watering) to minimize splashing spores onto leaves, and (4) clear away infected plant material. Fungicides are available, but usually not necessary and especially near the end of the growing season when plants are starting to dieback for the winter. More about powdery mildew.

Question: My bee balm is done blooming. When can I cut back the dead blooms?

Answer: You should deadhead (cut off) spent blooms on perennials like bee balm (Monarda) throughout the growing season. This improves the look of the plant, reduces the plant energy going into producing seed, and also can prompt a second, though typically smaller, re-bloom. About pruning perennials.

Question: When should you prune spireas?

Answer: When you prune a flowering shrub depends on whether the plant blooms in the spring (on old wood) or in summer (on new wood). If the plant blooms in the spring, it grows or "sets" flower buds for the next year within a few weeks of blooming, so it should be pruned within two weeks of flowering. If the plant blooms in the summer, flower buds are produced on the new spring growth, and it should be pruned in late fall or early spring before growth begins. More about pruning shrubs.

Question: I have a row of crabapples I have diagnosed as having apple scab. Is this something I can treat myself or do I need a professional?

Answer: Like all gardening problems, a correct diagnosis is critical before deciding on any mode of action. Apple scab can be managed by a home gardener with fungicides. More about managing apple scab.

P1250030.JPGLooking forward, Minnesota gardeners can reduce pests (diseases, weeds and detrimental insects) by choosing resistant plant cultivars and varieties that are suitable to the conditions of your site (light, soil, hardiness zone, etc.). It's also critical to a healthy landscape to space plants according to their mature size to ensure better air circulation and light to reach the plants, and the plants to achieve their natural form. Mulch plants and water at the base pf the plant to avoid splashing soil-borne pathogens (fungi, bacterial, etc.) onto lower leaves. Properly pruning plants and cleaning up dead leaves and other plant debris from your garden will also help reduce pests that overwinter in these materials.

Question: Is it OK to fertilize evergreens in September and October?

Answer: Time to stop fertilizing plants as fertilizing will prompt new growth. Our plants start to move into dormancy as the weather changes, and any new growth can be killed by cold weather. That said, be sure to keep watering your evergreens - and other woody plants - throughout the fall to help reduce the possibility of desiccation during the cold dry winter months. More about protecting trees from winter damage.

Question: We have some "critters" tunneling in our raised vegetable / flower beds and actually killing plants. What should we do?

Answer: Gardening with wildlife is always a challenge! Identify the animals first and try to determine how they entering your raised beds. You don't mention how your raised beds are constructed, so I am going to assume they are built in wood frames about 6-12 inches deep. Are the animals climbing into the beds? If so, hardware cloth fencing (very small wire grid) dug won below the surface and high enough to keep them out should help. Are they tunneling in through a hole or crack in your raised bed structure? If so, patch / plug the hole or crack. If they are entering from tunnels underground and if it's logistically possible, remove the soil, line the bed with hardware cloth, and put the soil back into the raised bed.

Repellents are also available, but often need to be reapplied and may not be available for the kinds of edibles you are growing.

Question: We recently lost two large birch trees in our landscaping near our house. We just had the stumps ground out. Can I replant another tree in that same spot?

Answer: Since you ground out the stump, then yes, you can replant. That said, before planting, try to figure out why the trees died - too close to the foundation, pest problems, poor soil, unsuitable conditions for the tree species - and try to correct the problem(s) before planting again. Paper birch do not do well in our urban conditions - compacted soil, heat, dry conditions, alkaline soil. Understand your soil and choose a new tree that will thrive in your soil, the amount of light and the space available (note the mature width of the canopy when you are looking at tree species). Then plant the tree correctly, provide adequate water and staking. More about planting trees.

Question: We are going to be over seeding our lawn due to bad winter damage. We live in sandy acidic soil. We have removed most of the moss. Can we seed and then lime?

Answer: Turfgrass species grow best in slightly acidic soil.  I would suggest having the soil tested to see what the pH is.  If the pH is below 6, then lime would be recommended to increase this slightly.  Turfgrasses grow best at a pH of 6.5.  You can lime anytime, either before or after seeding.  Basic soil tests are $17.00 from the University of Minnesota soil testing laboratory. If the pH is in fact low, there will be a recommendation on the soil test for how much lime to apply.  

Question: How do I get rid of creeping charlie?  

Answer: Creeping charlie can be an aggressive weed in many sites and has a particular competitive advantage over turfgrass in wet/shaded environments.  Herbicides used to control creeping charlie provide marginal success due to the waxy leaf surface that repels herbicide applications.  I suggest making an assessment of how much existing grass is in the lawn that you are trying to preserve.  If the lawn is 75% grasses, then I would suggest several applications of a selective broadleaf herbicide, which will control the creeping charlie and preserve the grass species.  The best herbicides for this include post emergent combination herbicides with the active ingredient triclopyr. Sometimes these herbicides are labeled as clover or oxalis killers.  Fall is the best time to apply these herbicides, and multiple applications spaced 2-3 weeks apart would generally be required for any success.  The the lawn is predominately creeping charlie, the best option would be to control it with a complete vegetation killer like Roundup (glyphosate) or diquat.  till several applications will be required.  Following successful control of the existing vegetation, seed shade tolerant turfgrass species such as the fine fescues or tall fescues.  If significant wet shade is present, rough bluegrass (Poa trivialis) is a species that might give you better results. More information on creeping charlie control.

Where to purchase grass seed.

Question: My back yard has always had a lot of moss. I've tried raking it out and seeding with grass seed but can't seem to get rid of the moss. Is there a way to get rid of the moss?

Answer: Moss is generally an indication of a poor environment for growing turfgrass, which includes shaded, moist, and compacted sites.  General recommendations for controlling moss in lawn situations would include reducing the amount of shade (pruning), aerating to help with water infiltration, reducing irrigation frequency, increasing the mowing height, and planting shade tolerant grass species.  Moss takes over and establishes in lawns with poor stands of turf, but rarely competes with the turf itself.  I suggest aerating to reduce compaction and pruning to improve light penetration and air movement.  Follow this by seeding with shade tolerant grasses: moist to dry shade- fine fescues or tall fescue, wet shade- rough bluegrass.  Moss controls on the marketplace will only have marginal success.  Start with the cultural control options to improve the health of your grass, followed by seeding.
Print Friendly and PDF