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Larry Sagers
Plantain broadleaf is a perenial plant with a taproot.

Most of us are enjoying the transition into fall with the changing seasons and the cooler weather. This is also a time to take care of tasks that will make gardening easier next year.

Among the important tasks is the perennial and often frustrating task of controlling weeds. Bring up the subject and gardeners complain, "That's all I've done all year. I'm tired and I need a break."

Because the task is so important, I will spend a couple of weeks trying to assist you. While the task might be never-ending, it is not something you can neglect. Weeds are always ready to overrun and destroy our gardens.

Give them an inch and they take a yard. Unfortunately, that is not 36 inches — it means your entire yard. Weeds are the most expensive pests to control in gardens. In your garden, you might not count the costs, but think of the time you spend controlling weeds.

Weeds cause more garden failures than any other pest. Insects and diseases damage various garden species, but weeds interfere with the growth of all desirable plants. Nothing reduces the overall production and beauty of the garden more than weeds.

I am often asked, "What makes a plant a weed?" Weeds are plants out of place. A desirable plant in one location is a weed if it becomes aggressive and overtakes more desirable plants.

Other definitions define a weed as a plant with objectionable characteristics or a plant that interferes with humans, domestic animals or wildlife. Because the definition of a weed is somewhat nebulous, the reason plants become weeds is not always apparent.

Weeds thrive in poor soil or other hostile conditions. They might have extensive stolon or rhizome systems and quickly invade planted areas.

Desirable plants in some areas are weeds in others. Bluegrass in a lawn is highly desirable, but in a flower bed it is a difficult problem. Scotch thistle, the national flower of Scotland grows as an ornamental in that country. In our dry climate, it is a horrible weed.

Weeds are copious seed producers. Each plant might produce more than 100,000 seeds in a single season and these disperse by many methods. Dandelion seeds spread with parachute-like structures that fly in the wind; cockleburs attach themselves to animals; puncture vines stick into tires and other seeds are eaten by birds or grazing animals and spread them in their droppings.

Weed seeds spread with irrigation water or soil and amendments. Weed seed longevity contributes to their persistence. Some weed seeds stay dormant for decades until they get the right temperature, light and moisture.

Weeds compete with your plants for water, nutrients, light and space. They harbor insects and diseases. Barbed seeds collect in clothing and are hazardous inside animals' ears or mouth.

Poison ivy, blue spurge and some other weeds cause severe skin reactions. Poison hemlock and other toxic plants cause serious injury or death if ingested. Puncture vines injure people, pets and bike tires. Weeds cause hay fever and other allergies and are also fire hazards.

Classifying weeds is a challenge but the process is critical for developing a control program. Weeds are most often classed by plant structure or life cycle.

Broad-leaved plants are dicots. They have veins that radiate from a larger vein. They typically have coarse root systems and many have tap roots. Grasses are monocots. They have long, narrow leaves, parallel veins and fibrous roots. Grasses are physiologically different so you can use selective herbicides for control.

Weeds are also classified according to their life cycles as annuals, biennials or perennials. These classifications are important to help you determine effective control measures.

Summer annuals grow from seeds that sprout in the spring, mature and reproduce before dying with the fall frost. Examples are barnyard grass, puncture vine, Russian thistle and pigweed.

Winter annuals germinate in the fall and the next spring they flower, produce seed and die before the summer heat. Examples are downy brome, chickweed, some mustards and wild oats.

Biennials have two year cycles. They grow vegetatively (without flowering) the first year. The next season they flower, produce seed and die. Thistles, mullein and hound tongue are biennials.

Perennials live three years or more. They flower and set seed without dying. Usually the tops die back in the winter but resume growth in the spring. Examples are quack grass, field bindweed, dandelion and plantain.

Knowing about weeds helps you control them. Next week's column will focus on specific weeds and how to best control them.

Garden tips

Apples Galore is a free apple and cheese tasting event for gardeners. Come satisfy taste buds and sample Utah's finest artisan cheeses and locally grown apples — the perfect combination for a perfect end to the season. Oct. 13, noon-2 p.m. at the Ogden Botanical Gardens, 1750 Monroe Blvd., Ogden, and that evening from 5 p.m.-7 p.m. at the Utah Botanical Center at 920 S. 50 West, Kaysville. See utahbotanicalcenter.org.

Thanksgiving Point is offering a class on fabulous fall color on Tuesdays, Oct. 11-25, 10 a.m. to 12:30 p.m. Cost is $40. To register, or for more information, call 801-768-7443 or visit www.thanksgivingpoint.com.

Larry A. Sagers is a horticulture specialist for the Utah State University Extension Service at Thanksgiving Point.