Prepared by Maher Jabado Oct 4-2013

Algae or Moss (on the Soil)


Algae and Moss are simple plant organisms. When given the proper conditions, either may be found growing on the surface of the growing soil. Algae appears as a green slime covering the soil. By themselves, neither is dangerous to plants. However, both should be considered as a warning that the soil is too wet and/or ventilation is too bad.

Associated problems:

-If algae is allowed to dry out, it can actually create a seal on the surface of the soil which may reduce the availability of oxygen and inhibit the soil's ability to absorb water.
-Once algae growth has started, itís difficult to stop it without under-watering your plant
-Algae and moss bring insect diseases; Fungus gnats and shore flies are lovers of such environment; These not only cause general nuisance when they are in adult flying stage but also could cause serious root damages when they are in larvae stage.

Fungus gnat adult caught on a yellow sticky trap

The shore fly (right) has a more
robustbody and shorter antennae
than a fungus gnat (left).

Fungus gnat larvae.

Shiny trails on the soil surface
made by fungus gnat larvae.



-The key to preventing the growth of Algae or Moss on the surface of potting soil is to make sure your plant is receiving the proper amount of water. Keep in mind that proper watering is not simply a factor of quantity and frequency. It is also a factor of how much water your potting soil holds relative to the amount of water your plant is able to absorb. If the soil holds more water than your plant can absorb, it may be the result of an over-watering program combined with inadequate drainage.

Usage if fans in small operation Fan tubes efficient in air exchange Larger operation using circulating fans

-If weather is humid (wet season) try to use a potting mix that is light and porous (i.e use coarser texture or mix with perlite). Also, unless your plants require different pH, try to use potting soil that has a pH between 5.8 and 6.2.(typical SAB substrate range)

-If potting soil product is used for seeding objective, you can help controling algae growth by avoiding light; In fact you don't need to have the seed under lights until there is germination, the factors in a seeds germination are temperature and water

Seed tray covered until germination starts


-Simple treatment: If you find that either Algae or Moss is growing on the surface of the soil, you will need to control watering and ventilation.
-Home made treatments, for small surfaces, and to avoid using chemicals, here are some home made recipies that could be tried; PLEASE USE THESE SUGGESTIONS WITH CAUTION; ALWAYS MAKE SMALL TESTING BEFORE APPLYING ON LARGER SCALE; Results could differ depending on water hardness and soil characteristics;
a) Water with light chamomile tea.
b) Mix 1 part grocery store peroxide: 9 parts water.
c) Spray the affected soil with a solution of 2-3 tea spoons baking soda mixed with 1 liter water.
-For larger surfaces, try to use chemical Algaecides; However that usage must be carefuly monitored specialy if plants grown are edible (i.e vegetables)