Algae On Seed Soil Surface: How To Get Rid Of Algae On Seeding Soil

By Bonnie L. Grant

Starting your plants from seed is an economical method that can also allow you to get a jump start on the season. That being said, the little sprouts are very sensitive to changes in conditions such as moisture and humidity. Excesses can cause damping off — algae growth on seed starting mix and other fungal issues. Read on to learn the reasons for algae on seed soil surface and how to prevent it.

Algae are plants but very simple rudimentary ones which lack roots, leaves and stems. They do photosynthesize but do not carry on traditional respiratory activities. The most common algae are probably seaweed, of which there are innumerable species. Algae require moist conditions, from soaking wet to boggy to humid. Algae growth on seed starting mix is common in cases where the site is moist and muggy. Such conditions promote the growth of these minute plants on your soil.

Help! Algae Growing on My Soil


The signs are unmistakable – a bloom of pink, green or even brownish sticky material sprawling across the surface of the soil. The tiny plant is not going to kill your seedling instantly, but it is a competitor for important resources such as nutrients and water.

The presence of algae on seed soil surface also indicates that you are overwatering. A good set up for growing seedlings may include a humidity dome to prevent the soil from drying out. Seedlings have algae on soil when the constant moisture is not balanced and ambient air is moist as well as the soil.

What to Do if Seedlings Have Algae on Soil

Don’t panic. The problem is easy to deal with and even easier to prevent. First, let’s focus on prevention.

  • Use a good quality seed starter soil, not just garden soil. This is because spores and disease may be contained in the soil.
  • Water only when the soil surface is nearly dry and don’t let your seedlings sit in a pool of water.
  • If you use a humidity dome, remove it at least once per day for an hour so the condensation can evaporate.
  • Peat pots and mixes with peat as part of the composition seem to have the worst problems with algae on seed soil surface. You can replace peat in your starter mix with fine bark dust. Avoid the use of mixes with a high proportion of peat.
  • Also, the seedlings may not be getting enough light. Move the pots to a bright sunny area or use plant lights.

How to Get Rid of Algae on Seeding Soil

Now we get to the question, “there is algae growing on my soil, what can I do?” You can completely repot the seedlings if they are large enough but this could damage tender new roots. Or you could also simply scrape off the affected soil surface or rough up the soil to prevent it from staying too soggy and forming algae blooms.

Some antifungal home remedies may also be of use. Use a bit of cinnamon sprinkled on the surface to get rid of algae on seedling soil.

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