Thursday, August 03, 2006

Crabgrass vs. wiregrass

John Arbogast

Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018

Or send an e-mail. Answers will be given only in this column. Please don't send pictures or samples.

Recent columns

Q: What is the difference between wiregrass and crabgrass?

A: A big difference is that wiregrass is a perennial that is practically impossible to control permanently when it invades a bluegrass or fescue lawn while crabgrass is a summer annual weedy grass that can be controlled in bluegrasses or fescues by making early spring and early summer applications of a pre-emergent herbicide to prevent germination of crabgrass seeds. Those seeds are needed for establishing the next crabgrass generation. The arrival of cold autumn weather kills all parts of crabgrass plants except for seeds. Those same temperatures will make wiregrass plants go dormant, not dead, until warm weather comes the following spring. Actively growing wiregrass can be killed in a lawn by applying a non-selective weed killer like Roundup that will kill good plants as well as the weedy grass. However, the injured wiregrass will come back in only a few years.

Now in mid to late summer here in Roanoke, crabgrass seedheads can be seen as slender upside-down “crows’ feet” growing above lawns that contain this weed. These seedheads are ripening crabgrass seeds that will fall into the lawn for next year’s weedy grass. Crabgrass seedheads will turn dark brown as cool weather arrives. Wiregrass reproduces by producing seeds in spring or summer plus vegatatively by even small pieces of its stems that can grow to big depths.

Another difference is their stimulation by lawn mowing. Crabgrass seems to grow in bluegrasses or fescues that are cut low, while wiregrass doesn’t care about lawn mowing height.

An easy-to-see difference is their anatomy. Crabgrass plants grow with stems that emerge from a central place like spokes of a bicycle wheel. Wiregrass spreads quickly by producing wiry stems that creep along the ground and stems that creep as much as several inches below ground.

Visual differences provide another clue. Wiregrass blades are short with narrow width (1/8 inch) and green color that helps them to blend into bluegrasses or fescues. Crabgrass blades stand out in a bluegrass or fescue lawn by their wider width (1/4 inch) and blue-green to yellow-green blades, especially now in mid to late summer here in Roanoke.

Q: I have questions regarding the Kay Parris magnolia grandiflora. The tag says that this is a rapid growing upright evergreen broadleaf tree growing to a height of 12 to 15 feet and spread of 15 to 20 feet. The tag says that the tree makes white flowers and likes sun. I’m not sure what this all means, especially rapid growing. I think that I paid too much for it but I wanted it. I am not sure it is the best tree for the yard now that it is planted.

A: If the mature size given on the tag fits your available area and is "in scale" with the height of your house and size of your yard, buying and planting the 'Kay Parris' variety of Magnolia grandiflora was most likely a good decision. If, after several years of nice growing conditions, you feel like this magnolia’s width seems “overwhelming”, you can “open up the area” by removing lower side limbs up to 8 to 10 feet. Keep in mind that mature size and growth rate are partly controlled by the plant's genes as well as site-specific characteristics including quality of soil (is the soil dark brown in color and easy to dig plus easy for roots to develop); sun or shade reaching the site; space availability (will your magnolia be crowded by other "things"?); moisture availability there; and nutrients in that soil as well as applied there. The absence of any requirements will affect your magnolia's ability to grow at the tag's rate. Once landscape trees and shrubs are planted, soil quality cannot be amended. However, you can help to make up for adverse conditions like droughty soil by watering once a week, using a water-saving device like a water weeping hose wrapped around under the branches or water dripping bag you’ve probably seen attached to tree trunks around Roanoke; poor or rocky soil by using 2 ½ inches of shredded organic mulch, and limited nutrients in that ground by applying a "tree fertilizer product" used according to manufacturer’s directions under the magnolia’s branches plus a little further out around your tree.

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