Defoliating Perennial Flowers | Deliberate Mechanical Defoliation of Perennials

This lesson is a scenario to accompany "Perennial Plant Response to Defoliation", which provides an opportunity to apply the concepts learn in that lesson to a real-life problem.

Marlene Wagner is a new Master Gardener who wants to keep beautiful but large chrysanthemums by her front door from getting so tall that they become leggy and flop over the sidewalk. She has heard that broadleaf perennials can be cut back but she doesn’t know how or when to do this without significantly delaying or losing the flowers or killing the plants.

She has also heard people use the words ‘pinching’, and ‘deadheading’, and ‘disbudding’ to describe cutting perennials—all of which sound like methods of inflicting pain. Pinching, deadheading, and disbudding are actually words used to describe slightly different methods of mechanical defoliation. Help Marlene decide whether any of these are appropriate in her situation.

Pinching is removing up to 1/3 of the growth to encourage production of side shoots and reduce height and promote a more dense and bushy habit. This happens because the apical meristem (growing point) also produces hormones that circulate through the plant and suppress branching from lower axillary buds. Removing the apical growing point removes the source of these hormones, and axillary branching is no longer suppressed. This technique delays blooming but the improvements in overall habit and appearance is worth it.

Deadheading is removing spent flowers to reduce seed production and encourage rebloom. A plant’s main goal is to survive and multiply. It does this by producing seed that have the potential to grow into more plants. By removing spent flowers, the plant will continue to try to produce seed by developing more blooms. Also, it will not be putting energy into producing seeds. Rather, it can use this energy to produce more flowers. This is typically used in managing annuals, but also helps keep perennials tidy.

Quiz

Question

Question: Which of the following is NOT one of the three important things to know in order to determine how the plant will respond after defoliation?

A. Where the growing point is located.

Incorrect: The location of the growing point throughout the season is critical in predicting the response of a plant after defoliation. Removing the apical meristem, (main growing point), stops production of hormones that suppress branching. Removing all axillary growing points forces the plant to initiate new growth form once dormant crown buds. The time during the growing season when plant tissue is removed determines the response of the plant. Removing tissue during the wrong time can negatively impact the plant both short term and long term. Removing tissue too late does not allow the plant enough time to re-grow and restore used carbohydrate reserves before the end of the growing season. The amount of residual leaf area remaining after defoliation must be adequate for continuing photosynthesis in order to get significant re-growth.

B. Whether the plant is growing in sun or shade.

Correct: The location of the growing point throughout the season is critical in predicting the response of a plant after defoliation. Removing the apical meristem, (main growing point), stops production of hormones that suppress branching. Removing all axillary growing points forces the plant to initiate new growth form once dormant crown buds. The time during the growing season when plant tissue is removed determines the response of the plant. Removing tissue during the wrong time can negatively impact the plant both short term and long term. Removing tissue too late does not allow the plant enough time to re-grow and restore used carbohydrate reserves before the end of the growing season. The amount of residual leaf area remaining after defoliation must be adequate for continuing photosynthesis in order to get significant re-growth.

C. When during the growing season the plant was (will be) defoliated.

Incorrect: The location of the growing point throughout the season is critical in predicting the response of a plant after defoliation. Removing the apical meristem, (main growing point), stops production of hormones that suppress branching. Removing all axillary growing points forces the plant to initiate new growth form once dormant crown buds. The time during the growing season when plant tissue is removed determines the response of the plant. Removing tissue during the wrong time can negatively impact the plant both short term and long term. Removing tissue too late does not allow the plant enough time to re-grow and restore used carbohydrate reserves before the end of the growing season. The amount of residual leaf area remaining after defoliation must be adequate for continuing photosynthesis in order to get significant re-growth.

D. The amount of green tissue (leaf area) left after defoliation.

Incorrect: The location of the growing point throughout the season is critical in predicting the response of a plant after defoliation. Removing the apical meristem, (main growing point), stops production of hormones that suppress branching. Removing all axillary growing points forces the plant to initiate new growth form once dormant crown buds. The time during the growing season when plant tissue is removed determines the response of the plant. Removing tissue during the wrong time can negatively impact the plant both short term and long term. Removing tissue too late does not allow the plant enough time to re-grow and restore used carbohydrate reserves before the end of the growing season. The amount of residual leaf area remaining after defoliation must be adequate for continuing photosynthesis in order to get significant re-growth.

Looks Good! Correct: The location of the growing point throughout the season is critical in predicting the response of a plant after defoliation. Removing the apical meristem, (main growing point), stops production of hormones that suppress branching. Removing all axillary growing points forces the plant to initiate new growth form once dormant crown buds. The time during the growing season when plant tissue is removed determines the response of the plant. Removing tissue during the wrong time can negatively impact the plant both short term and long term. Removing tissue too late does not allow the plant enough time to re-grow and restore used carbohydrate reserves before the end of the growing season. The amount of residual leaf area remaining after defoliation must be adequate for continuing photosynthesis in order to get significant re-growth.

To review this concept click on the link: Perennial Plant Response to Defoliation - An Overview: Defoliation of Grasses and Broadleaves.

Development of this lesson was supported in part by the Cooperative State Research, Education, & Extension Service, U.S. Dept of Agriculture under Agreement Number PX2003-06237 administered by Cornell University, Virginia Tech and the American Distance Education Consortium (ADEC) and in part by the New Mexico and Nebraska Agricultural Experiment Stations. Any opinions,findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.