Weed Management

Weeds compete for water, nutrients, and light, resulting in reduced flower yields and an increased threat of serious insect and disease problems. On this page, you’ll find information on weed management and control in ornamentals and floriculture, including poison hemlock, horseweed, carpetweed, mulberry weed, ragweed, and multiflora rose. Find tips on organic land care and weeds in the field.

Weeding in Floriculture

Controlling weeds is important – they can be unattractive, but more importantly, they compete with flowers and ornamentals for light, nutrients, and water. They can also harbor insects and increase issues with disease. But what makes a plant a weed? Many people define a weed as a plant that’s in the wrong position, or that interferes with the management objectives for a particular site or situation.

Keeping weeds under control is essential, not just for homeowners but for green industry professionals as well. It also plays a key role in organic land care best management practices and creating healthy landscapes.

Different floriculture practices require different weed management approaches. Weeds can be a big problem in greenhouses, both production and retail greenhouses. They grow underneath the benches and can be a host for pests and a reservoir for diseases. Managing weeds in cut flowers requires different approaches depending on the specific weed, flower, or woody stem, as well as the time of year and level of infestation.

Identifying and Managing Invasive Plants and Weeds

Weeds can be bothersome, but there are some species you should avoid at all costs. The Pennsylvania invasive plant list includes burning bush, privet, Japanese barberry, and the butterfly bush. Penn State Extension runs a workshop that will help you learn about the impact of invasive plants and how to identify and control them.

Some of the more common weeds include:

• Japanese honeysuckle: This non-native climbing vine prefers full sun, although it can grow in shaded environments. Growth is aggressive and it will quickly climb over other desirable plant material.
• Wild carrot or Queen Anne's lace: This biennial is not considered a weed by everyone, but if grown in landscape beds it may require control.
• Jimsonweed (Datura stramonium): This annual plant is poisonous to animals and humans. If left undisturbed, it has the potential to be the tallest unwanted plant in a landscape bed, reaching more than 5 feet tall.
• Multiflora rose: The State of Pennsylvania lists this as a “Class B” noxious weed. The dense monocultural thickets it creates degrade natural environments and reduce native plant and wildlife diversity.
• Poison hemlock: It is poisonous to animals and humans and commonly found along roadsides, fields, and wet areas. It is very similar in appearance to wild carrot.
• Mulberry weed: This summer annual can grow to more than 2 feet tall and will produce multiple, shorter stems when the crown is broken.
• Ragweeds: These are members of the Aster family and are particularly resistant to herbicides.
• Carpetweed: It is an annual that can be a weed issue in ornamental plant beds and in newly established or thinning turf.
• Horseweed: Common in landscapes, nurseries, and agricultural settings, it is a prolific seed producer. One plant can produce more than 200,000 seeds that can be windblown up to a quarter of a mile.
• English ivy: It is used extensively in landscapes as ground cover, but if left to grow unchecked it can climb into trees, cover the foliage, and kill the branches.

Herbicide Application for Flowers and Ornamentals

Weed control in floriculture is critical because maintaining the beauty of the flowers and ornamentals is important. Implementing a weed control plan is imperative, as it is much easier to prevent weed growth rather than kill existing weeds.

A common practice in floriculture is the application of herbicides. Most combination herbicides are formulated in two ways: amines or esters. Understanding the difference between the two and when to use them can increase the effectiveness of your weed control dramatically. Using the proper herbicide formulations also prevents damage to non-target plants. Herbicide drift and drift-related damage can be costly and there’s also the risk of a potential lawsuit. Spray recordkeeping is key when you apply herbicides or pesticides.

If you choose to apply or supervise the use of restricted-use pesticides, federal law and regulations state that you must be certified as a private or commercial applicator.