Is Yeast a Super Fertilizer for Plants?

The hottest new trend is to fertilize plants with a magical “superfood” fertilizer made from yeast. Is this a good idea? Is it a good fertilizer? Does it grow better plants? Let’s look at the facts.

How to Make Yeast Fertilizer

The yeast fertilizer recipe is very similar to making bread and starts with activating the yeast. Mix one pack of dry yeast (1 teaspoon), one teaspoon sugar and one cup of warm water. Let sit for 3 hours to give the yeast time to grow. Dilute with 5 cups of water and use this to water your plants.

If you check the internet there are many recipes and mixture ratios. No one explains why their recipe is correct or why it is better. If it is used outdoors it is usually diluted even more.

What is the Best Yeast Recipe?

Does the recipe make a difference? Not really. The total amount of nutrients in the mixture come from the starting yeast and a tiny bit comes from the water. Sugar has no plant nutrients and the growing yeast do not create more. Saccharomyces cerevisiae, Baker’s yeast, does not fix nitrogen, nor does soil based yeast.

Since nutrients are not created during the yeast growth phase, the actual method used does not really matter. The total amount of nutrients depends on the amount of yeast used.

Is Yeast a Fertilizer?

A fertilizer is legally defined as having reasonable amounts of nitrogen, phosphorus and potassium. Anyone who suggests this is a fertilizer should be able to give you the NPK value. Since gardening sites don’t provide this kind of information, they have no idea if their mixture is a fertilizer or if it is useful for plants.

I did find a study done in Egypt that tested yeast extract and provided nutrient data. Unfortunately, they don’t provide details of how they made this extract except to say it was a mixture of dry yeast, sugar and water. After activating the yeast, it was then frozen and thawed twice to disrupt the yeast cells and release the nutrients inside. The recipes used by home gardeners skip this step and so the nutrients inside the cells will be released more slowly.

Based on this data, the yeast extract in this study has an NPK of 7-0.4-0.8. This was then diluted to produce the final fertilizer which had an average NPK of 0.04-0.002-0.004. For comparison, a Miracle-Gro 24-8-16 diluted for houseplants has a final NPK of 0.024-0.008-0.016, which is the ideal ratio for plants. The yeast fertilizer has enough nitrogen, but is low in phosphorus and potassium. It does have low levels of some micronutrients.

You can use it as a nitrogen source, but for an ideal fertilizer you’ll have to augment it with phosphorus and potassium from another source.

Biostimulants and Plant Growth Regulators (PGR)

There is a lot of talk about biostimulants and PGRs, improving plant growth. Yeast fertilizers do contain compounds like amino acids and vitamins but so does just about every organic material. There is nothing special about the ones found in yeast, nor are the amounts particularly high.

What Does Science Say?

A comprehensive review of yeasts as biofertilizers from 2021 had this to say, ” the use of yeasts as PGPMs (plant growth-promoting microorganisms) has not been extensively investigated”. Most of the studies that do exist have focused on yeast found in soil and not Baker’s yeast.

One study found that spraying apricot trees with yeast increased the weight of fruit produced, but not as much as a spray of organic fertilizer (mega power-x). Spraying pea plants with yeast in sandy soil increased the total number of pods by one-half pod per plant . Not a significant increase for gardeners.

Other studies have combined Baker’s yeast with organic fertilizer, other organic waste products, and even synthetic fertilizer. The yeast may have contributed to better growth, but the data is very preliminary and usually does not separate out the effect of the yeast.

I did not find a study that tested the Baker’s yeast fertilizer used by gardeners.

Which Plants Like Yeast?

The compounds produced by yeast include biostimulants and nutrients. These generally have similar effects on all plants. If yeast fertilizer works on some plants it probably works on all plants.

Yeast-based Crop Protection Spray 

Some claim that the above yeast mixture will also protect plants from various diseases such a blight and fungal infections. Yeasts typically do not produce any toxic metabolites which makes it less likely that they attack pathogens. However, special strains of Baker’s yeast have been found to produce toxic proteins that degrade the outer cell wall of competing yeast. These were causing havoc in the beer industry and you can find more details on this interesting story in Food Science for Gardeners.

Yeasts, like all microorganisms, compete with other organisms, including plant pathogens, for nutrients and space. This is probably the main way in which they compete. They also colonize plant surfaces, especially in damaged areas, where the plant is most prone to infection by pathogens. As they grow they remove nutrients making it harder for pathogens to grow.

Although yeasts have the potential to protect plants from disease, few commercial products use them for this purpose and there is no research to show that a spray of Baker’s yeast will reduce pathogens on plants.

Does Yeast Fertilizer Work?

The answer really depends on how you want to ask the question.

Do plants grow better with yeast fertilizer – yes. The yeast does provide nutrients and those will help plants grow in low nutrient environments.

However, if you ask, does yeast fertilizer work better than other forms of fertilizer, then the answer is no. There seem to be no special properties in the yeast mixture. Their effect on plants is similar to other organic or synthetic fertilizers. It does however smell better than fish emulsion.

If you have some extra yeast to use, by all means use it in the garden or on your house plants. But there is no reason to make up a mixture specifically to use on plants. Make bread with it instead.

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