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Lecture 1: Goals & Principles

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Primarily aesthetic — maintain and improve the visual quality of the landscape


Functional: weeds can affect safety, health, allergies, insect and diseases

Poison ivy causes allergic dermititis

Poison ivy causes allergic dermititis

Sandbur can be a real pain in bare feet

Sandbur can be a real pain in bare feet

Ragweed pollen causes allergic "hay fever" in many

Ragweed pollen causes allergic “hay fever” in many

Principles: 5-step process (Handout: Plan Before You Plant)

Recommended (strongly) reading:
Plan Before You Plant — A 5-Step Process for Developing a Landscape Weed Management Plan

Step 1. Site assessment

Key weeds – perennial broadleaves and sedges
Grassey weeds can be controlled postemergently with selective herbicides

Ask yourself the question: “Can I control these weeds after Planting?”

Step 2. Define the Planting: 5 Types of Landscape Plantings

The type of planting will define the post-plant weed management options and the importance of pre-plant weed control.

  1. Woody tree & shrub beds — Most post-plant weed management options
  2. Woody groundcover beds
  3. Annual beds
  4. Perennial beds
  5. Mixed planting — Fewest post-plant weed management options

Step 3. Selection of ornamental species and compatible weed management options.

Example 1: Florida betony cannot be selectively controlled in beds planted to herbaceous ornamentals. Therefore, opting for a woody planting instead will make maintenance easier by allowing the use of effective herbicides.

Example 2: Yellow nutsedge can be controlled with preemergence applications of Pennant Magnum in Ageratum or Petunia beds but not in Begonia or Coleus.
If yellow nutsedge has been a problem in the past – plant petunias instead of coleus.

Table 1. Weed management options and limitations for the five types of landscape plantings.

  • Geotextiles and mulches are useful.
  • Many broad-spectrum herbicides are available for pre- and postemergent control.
  • Spot or directed applications of non-selective herbicides, like Roundup, are possible.
  • Therefore: species selection is flexible and pre-plant weed control is not as critical.

Recommendations: Control perennial weeds before planting (although control may be possible after planting), use geotextiles with a shallow layer of mulch, use a preemergence herbicide if needed, and supplement with spot applications of postemergence herbicides and/or hand weeding.

  • Limited uses for non-selective herbicides; therefore, control perennial weeds before planting
  • Do not use geotextiles where ground covers are expected to root and spread.
  • Control annual weeds with mulching, hand weeding, and/or herbicides.
  • Several preemergent herbicides are available.
  • Few uses for postemergence herbicides
  • Postemergence control of annual and perennial grasses is possible.

Recommendations: Control perennial weeds before planting, use geotextiles where possible; else use mulches with a preemergence herbicide and supplement with hand weeding.

  • Periodic cultivation (annually or between display rotations) will suppress many weeds.
  • Very limited use of non-selective herbicides; control perennial weeds before planting.
  • Geotextiles generally are not useful (due to the short-term nature of the planting)
  • Few preemergent herbicides are safe; careful species and product selection are required.
  • Mulches will suppress many annual weeds.

Recommendations: Control perennial weeds before planting, carefully select species for weed management compatibility, use mulches, a preemergence herbicide, and hand weeding.

  • Lack of periodic cultivation will encourage perennial weed encroachment.
  • Fewer herbicides are labeled; check the labels carefully.
  • Geotextiles may useful in clump-type plantings or to restrict growth of spreading-types.
  • Very limited use of non-selective or postemergence herbicides.

Recommendations: Control perennial weeds before planting, use geotextiles where possible, use mulches with a preemergence herbicide (where possible), and supplement with hand weeding.

  • More complex due to the diversity of species.
  • Different areas of the bed could receive different treatments.
  • Site preparation is usually critical.
  • Few herbicides are registered for a wide spectrum of ornamental plant types.
  • Geotextiles may or may not be useful.

Recommendations: Maximize the number of weed control options by compatible species selection. Control perennial weeds before planting, use geotextiles where possible, use mulches with a preemergence herbicide where possible, and supplement with hand weeding.

Step 4. Site Preparation: 

Goal: eliminate weeds that cannot be controlled after planting
Non-selective herbicides
Fumigation (last resort with no other options are available)

Step 5. Installation and implementation.

  • Site preparation and sanitation.
  • Mulches
  • Preemergence herbicides
  • Postemergence herbicides

Study Questions:

  1. What are the 5 types of landscape plantings?
  2. List the types of landscape plantings in order from the most to least post-plant weed control options.
  3. Give an example of how landscape plant selection can influence your weed management choices.
  4. What are the key weed management option differences between the 5 landscape bed types?
  5. Following a site assessment — What is the key question you ask yourself (and answer) concerning the weeds present in a proposed landscape planting?