Q: Last fall, my mums developed black spot for the first time. I sprayed them and cut off the dead stalks, but am worried about it returning this year. Will the mums come back? Should I just dig them up and get new plants? Will my other plants develop black spot this year?
A: Without seeing the plant, I can’t be sure, but it sounds like your mums developed pseudomonas cichorii, commonly known as bacterial leaf spot. Symptoms of this disease are leaves that develop tan to dark brown spots that are sometimes outlined in yellow. There may be prominent signs of blemishing along the leaf veins (the leaf veins act as barriers to the spread of the bacteria). The leaves may wilt and the whole plant can die. This bacteria can live on in infected plants; in the contaminated soil; in leaf, stem and flower debris; in infected seed; and also in the pots they were grown in and on garden tools. Bactericides are of limited benefit. The plants cannot be cured.
Remove the entire plant as soon as you notice the disease on the plant, as well as those nearby to prevent the spread of the disease. Practice vigilant sanitation by regularly cleaning up fallen leaves and other plant debris. Disinfect all garden tools that came into contact with the mums with a bleach/water solution.
I suggest digging out any mums that have survived the winter. Replace them with another late summer/fall blooming plant such as Sedum ‘Autumn Joy.’ Avoid planting mums or any other plant that is a member of the Asteraceae family in that area for several years as an extra precaution, and only plant those chrysanthemums that claim resistance to bacterial leaf spot. Water the plants at soil level rather than sprinkling the leaves with water.
For more information, consult The Ohio State University (OSU) Fact Sheet HYG-1219-92, “Growing Chrysanthemums.”
Q: I noticed this spring that tree roots are very exposed in our lawn where we have a red maple tree. Should we try to cover those up with soil or leave them be?
A: The first tendency for gardeners when faced with exposed tree roots is to add more soil around the base of the tree to cover the root system. Unfortunately, adding soil to the existing grade of the tree will create reduced oxygen levels for tree roots. Roots that suffer from the lack of oxygen lead to branch dieback. If the tree is healthy, this may occur slowly, over a period of time. Low-growing ground covers or mulching are recommended around trees when the trees’ roots are at the surface and cause mowing problems.
- Ground covers: First remove all grass and weeds from the area. Hand pull the plants from among the tree roots. Spread a mixture of topsoil, organic matter such as humus or composted manure and an all-purpose fertilizer in between the tree roots to a depth of no more than 1 to 2 inches.
Now plant the ground cover among the tree roots in a careful manner to minimize damage to roots. Choose a plant that grows vigorously but is not invasive to quickly fill in the area and shade out weeds. Select a ground cover that is well-suited to the conditions of the site. Space plants according to their rate of growth and growth habit. Plant under the tree’s canopy but away from its trunk. Closer plantings will fill in faster, but it is not necessary. Water well, but do not overwater. Ordinarily, 1 inch of water applied every five to seven days is sufficient, but the new plants will be competing with the tree roots for water, so keep a close eye on moisture.
For more information, request Fact Sheet HYG-1648-01, “Herbaceous Groundcovers for the Home Landscape,” from The Ohio State University Summit County Extension Hotline at 330-928-4769, ext. 3, Tuesdays from 9 a.m. to noon.
- Mulch: Mulch is a valuable tool to keep the areas around woody plants weed free.
Research shows that root density of mature trees, such as red maple trees, is greater under mulch than in bare soil, and much greater than under turfgrass. That’s because turfgrass roots have an advantage over tree roots because of their greater density and their nearness to the surface of the soil. This is especially true during periods of drought. Ideally, the mulched zone should radiate from near the trunk out to the area under the tree directly below the canopy and stopping at or slightly beyond the drip line (the outer edge of the tree’s leaf canopy where water would drip from after a rain).
The greatest benefits of mulching are conserving soil moisture and moderating soil temperature. Both organic and inorganic mulches slow evaporation that increase soil moisture, with organic mulch the most effective. Organic mulches also can increase the fertility of the soil as it decomposes.
Mulch should be applied no deeper than 3 inches around trees, beginning with a shallow application 6 inches from the trunk and then progressing to a full 3-inch depth extending to the drip line.
Never allow the mulch to touch the trunk of a tree or any woody plant, for many good reasons. Among others, it can create a condition of constant moisture, which is harmful because it interferes with the tree’s exchange of oxygen and carbon dioxide with the atmosphere commonly referred to as drowning.
It can also cause fungal cankers, root rotting and root girdling, where a tree root encircles the base of the tree and cuts off the flow of nutrients, causing dieback in part of the tree.
It also can attract moisture-loving insects, such as carpenter ants.
Request Bulletin 894, “Using Mulches in Managed Landscapes” from Ohioline, or visit ohioline.osu.edu/b894/pdf/b894.pdf for a comprehensive article on mulch in the home landscape.
Q: What is the difference between hay and straw?
A: In a nutshell, hay is a food to be eaten by livestock. Straw is used for livestock bedding, mulch and many other uses.
Specifically, hay is a tall field grass. The entire plant, including seed heads, is cut to ground level at maturity and left in place to dry in the sun. Once dried, the hay is baled into rectangular-shapes and used to feed many different types of animals, from domestic farm animals to wild zoo animals.
Straw is the stemmed byproduct remaining after seed heads such as wheat, rye and barley have been harvested. The straw is baled in rectangular bales similar to hay, but is inedible. Straw has a myriad of uses. It is the main staple for warm bedding for animals in barns and stables. It can also be used as a cover for newly planted lawns and for mulching vegetable gardens.
For more information, call The Ohio State University Summit County Extension Hotline. Please note fact sheets are sent out free; there is a fee for bulletins. Many bulletins are available online at ohioline.osu.edu and can be printed from home or accessed at the public library.
Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and course work in botany, geology and wildflowers. Davis is a master gardener emeritus under The Ohio State University’s Horticultural Extension. Readers can send in questions regarding lawn and garden issues, which could be featured in a future edition, as well as about the OSU Master Gardener program. Questions can be emailed to firstname.lastname@example.org, faxed to 330-665-9590 or sent to Leader Publications, 3075 Smith Road, Suite 204, Akron, OH 44333. Please do not send any leaves, seeds or other organic material. Inquiries about area garden clubs or groups should be sent directly to the particular organization in question.
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