Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001801
11/12/99
USING ORGANIC MULCHES
When to Apply Mulch
Apply an organic mulch on most established ornamental
plants in midspring when the soil has warmed sufficiently
for active root growth. If applied before this time, the
mulch will keep the ground cool and root growth of
ornamental plants may be slow. Apply an organic mulch
around newly set ornamental plants after they are put into
place and thoroughly watered.
How Deep to Apply Organic Mulches
For best results, apply mulch at least 2 to 4 inches deep
over the whole area during spring, summer and early fall
but avoid covering the crowns of very low-growing
ornamental plants. Tender ornamentals that need winter
protection may require an additional 1 to 2 inches of
mulch around the crowns or bases of the plants during the
winter. In the spring, this added mulch should be fanned
out or away from the stems or crowns of the plants before
more material is added for a summer mulch.
Fertilizing Organically Mulched Plant Material
As indicated previously, mulching with many organic
materials--including wood chips, sawdust, straw or
shredded bark--means you must apply extra fertilizer
around the plants to reduce the chance of nitrogen
deficiency or starvation. Apply 1/4 pound of ammonium
nitrate or ammonium sulfate for each bushel of mulch
material used on the bed, or 2 pounds per 100 square feet
of a complete fertilizer such as 5-10-5, 12-12-12 or
similar analysis. This fertilizer should be applied
before the mulch is placed on the soil, or in early spring
before more material is added to plants already mulched.
If the lower foliage yellows and the plants lack vigor
during early summer, apply additional fertilizer.
Do Not Overmulch
The roots of plants need a constant supply of oxygen at
all times. Overmulching kills the roots of shallow-rooted
plants by suffocation.
Symptoms of too much mulch include chlorotic foliage
(symptoms often resemble iron deficiency), abnormally
small leaves, poor growth and dieback of older branches.
Disease organisms that are active under conditions of low
oxygen and excessive moisture can become active and attack
the roots. Sometimes the old root system will be rotted
as the plant tries to send out new roots into the mulch
layer. Excessive amounts of mulch applied around tree
trunks can lead to cankers on susceptible species.
This information is for educational purposes only. References
to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
Extension. Reprinting cannot be used to endorse or advertise
a commercial product or company.
This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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