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Starch Water for Plants: Everything You Need to Know

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Liquids produced in the kitchen can be used to water plants because of the nutrients they contain. Starch water is produced from boiling starchy vegetables, which can be used to fertilize plants.

Starch water is a natural, organic solution that can be used to improve the health of your plants and flowers. It contains no chemicals or additives and is free from any harmful side effects, and can be used to water plants because it provides (NPK) fertilizer and minerals for plants to use while promoting a healthy bacteria population effectively.

This type of water produces beneficial nutrients for growing plants in the greenhouse, but what exactly is starch water? And how does it work? Let’s find out!

Using Starch Water for Plants

Starch water for plants

The first thing you need to know about using starch water for plants is that it is safe to use on all types of plants. This includes vegetables, fruits, herbs, and flowers. 

The most common use for starch water is as a fertilizer for houseplants and indoor flowering plants. It is also used by gardeners who grow vegetables outdoors. Plants use glucose for energy and to make other substances like cellulose and starch. Cellulose is used in building cell walls. Starch is stored in seeds and other plant parts as a food source.

What does Starch Water do for Plants?

Starch water provides an energy source for plants by direct application, which can then be absorbed both by the leaves and the roots.

Although plants may seem stationary, there are a lot o biological reactions occurring within the plant that never stops. All these reactions require energy in order for them to follow through.

For example, Plants use photosynthesis to convert carbon dioxide into organic compounds. In order for this process to occur, plants must have enough oxygen available.

Good soil aeration

This oxygen is derived both from the plant and the atmosphere. The underside of the leaf has openings called the stomata which, as stated, open and close to let gas in and out of the plant. This requires energy.

Now imagine this process taking place in millions of cells all at once, both day and night (in some plants). That’s a lot of energy being used. Therefore, there is some sort of goto energy storage for the plants to use.

Supplying this water to the plants helps in this process and boosts the overall health and growth of the plants.

When applying water to my plants, I use a cost-effective and durable watering can that I got on Amazon, which makes watering fun and easy without any spillage. 

MyLifeUNIT Plastic Watering Can

What Function does Starch have In Plants?

Starch is a polysaccharide that can be found in many plants, including corn, wheat, rice, potatoes, tapioca, amylopectin, amylose, glycogen, and dextrin. It is composed of glucose units linked together by α-(1→4) glycosidic bonds.

Plants use starches as energy storage for growth. They store carbohydrates in their leaves or stems during times when they are not growing.

Plants need Starch for Photosynthesis

The Process of Photosynthesis

When the plant needs energy, the stored carbohydrate is converted into sugar and released through photosynthesis.

Photosynthesis is the process that plants use to convert carbon dioxide into carbohydrates. This process is called autotrophic respiration. The process occurs in two stages: light reaction and dark reaction.

During the light reaction, chlorophyll absorbs sunlight and converts water and carbon dioxide into glucose and oxygen.

Then during the dark reaction, the plant uses the energy from the sun to create ATP which provides the energy for the cell to grow.

Is Starch Water Good for Plants

Plants can easily absorb the dissolved starch in water because of the dissociation that the water allows.

The starch is then transported to various parts of the plant, such as the stems and leaves, where it is stored.

Starch is a quick source of energy for plants to use. Think of it like an energy drink to humans; even though it may not react as fast (we know plants are slow), it has a generally positive effect on how fast biological reactions are conducted within the plant.

What are the benefits of Starch Water for plants

  • Boosts growth
  • Creates a healthier plant
  • Stimulates photosynthesis
  • The plant produces larger, greener leaves
  • Prompts larger root growth
  • A healthier plant can easily ward off pests and disease

Is Starch Water Bad for Plants

Starch is a complex form of sugar.

Sugar normally attracts unwanted insects such as flies and ants, therefore if too much starch water is applied to the plant or it is allowed to sit for long periods of time in the soil or on leaves, it will start attracting pests. Ants eat plants for food, they also use them to build nests.

They will collect the starch from the watered plant and store it in their stomachs until they need it later. 

Plants naturally produce sugary sap or honeydew, which can attract insects, and with the additional starchy water, the problem may get out of hand.

Starch can smell when it goes bad. It will begin to spoil when allowed to sit for long periods, apart from attracting insects. 

Plant Pests

Expired starch water is not a sent for a sensitive nose as it can produce an unpleasant odor. No one wants a smelly plant, so it is recommended that starch water be applied intermittently or through the bottom watering method, which we will explain further in this article.

Types of Starch Water for Plants

Starch water can be produced from any kitchen ingredient rich in starch.

Potato Starch Water for Plants

potato water for houseplants

Potato water is nutrient-rich water obtained from boiling potatoes.  Potatoes contain minerals and nutrients that can be used to fertilize plants.

This water can supply plants with over 350mg potassium (K) per 100g, a macronutrient used by plants to develop immunity to environmental stress, along with phosphorus, magnesium, calcium, and zinc.

It provides the plant with an organic source of nutrients that promotes plant growth while preventing deficiencies associated with low potassium (K) levels, including brown scorching and curling of leaf tips.

Potassium helps plants grow strong stems and leaves, which increases the plant’s ability to absorb water from the soil.

Plants also use potassium for energy production, which allows them to grow faster. Add potassium fertilizer to your garden if you want to feed your plants well.

Rice Starch Water for Plants

Using Rice Water on Plants

Rice water can be used to water plants because it provides a sufficient amount of (NPK) fertilizer and minerals for plants to use while promoting a healthy bacteria population effectively.

This results in healthy plant growth. It can also be applied using any method and can also ward off unwanted pests when fermented.

Rice water is the water derived either from boiling or washing rice. Rice is a well-known food staple and feeds millions every day.

You don’t have to use the rice and throw it away. Rice water can be obtained as a byproduct of your everyday cooking routine and it reduces waste by reusing the remnants of the rice from washing or soaking.

The nutrients in 60 grams of cooking rice are as follows –

NutrientsBrown riceWhite rice
energy82 calories68 calories
protein1.83 g1.42 g
total lipid (fat)0.65 g0.15 g
carbohydrates17.05 g14.84 g
fiber, total dietary1.1 g0.2 g
sugars, total0.16 g0.03 g
calcium2 milligrams (mg)5 mg
iron0.37 mg0.63 mg
sodium3 mg1 mg
fatty acids, total saturated0.17 g0.04 g

The most dominant mineral from the table is calcium which comes in at 5mg per 60 grams of rice.

Calcium is a secondary nutrient that is critical to crop development. It is needed in large amounts by all plants for the formation of cell walls and cell membranes, and it plays a vital role in soil structure.

Plants also need calcium to make chlorophyll. Chlorophyll makes plants green and helps them absorb sunlight. 

Symptoms of deficiency include the death of growing points, premature shedding of blossoms and buds, tip burn, blossom end rot, and bitter pit.

Pasta Starch Water for Plants

Using Pasta water on plants

Pasta water can be used to water plants because it provides (NPK) fertilizer and minerals for plants to use while promoting a healthy bacteria population effectively.

Like rice water, pasta is the water drawn from pasta from boiling or soaking in water. It contains starches that can feed the bacteria in the soil. These starches are made from the natural ingredients of flour, eggs, and water.

This results in healthy plant growth. Pasta water can also be applied using any watering method and can also ward off unwanted pests when fermented.

Nutrients in one Cup of Cooked Spaghetti 

NutrientsNutrient Count
Protein7.5 grams
Carbs37 grams
Fiber6 grams
Fat0.8 grams
Manganese97% of the RDI
Selenium52% of the RDI
Copper12% of the RDI
Phosphorus12% of the RDI
Magnesium11% of the RDI
Iron8% of the RDI

*RDI – Recommended Daily Intake

The dominant mineral from the table above is manganese. 

Manganese (Mn) is an important micronutrient for plant growth and development and sustains metabolic roles within different plant cell compartments.

It is also required by plants in the second greatest quantity compared to iron.

Manganese deficiency symptoms, which often look like those of iron deficiency, appear as interveinal chlorosis (yellow leaves with green veins) on the young leaves and sometimes tan, sunken spots that appear in the chlorotic areas between the veins.

Plant growth may also be reduced and stunted.

Banana Peel Starch Water


Banana peel water is a nutritional kitchen byproduct that can be used to fertilize plants because the minerals it contains are essential for plant growth and development.

When extracted from banana peels, minerals and nutrients can be used to fertilize plants. Banana peel water supplies plants with a substantial amount of potassium (K), a macronutrient that is used to develop immunity to environmental stress and pests while at the same time promoting healthy plant growth.

Banana is a good vitamin C, dietary fiber, manganese, and potassium source.

Banana peels can be boiled, which causes the minerals within the peel to be leached out into the water. What you have in the end is starch water rich in potassium.

The nutrition facts for 1 medium-sized banana (100 grams):

MineralQuantity (mg/g)Used For
Potassium (K)78.10The movement of water and nutrients, Regulates photosynthesis
Magnesium (Mg)31.9Promotes photosynthesis and green leaves
Manganese (Mn)76.20Root growth and resistance to pathogens, Photosynthesis
Sodium (Na)24.30Helps with metabolism and synthesis of chlorophyll
Calcium (Ca)19.20Provides structural support to cell walls
Iron (Fe)0.61Synthesis of chlorophyll and Green leaves

As seen in the table above, banana peels are rich in potassium, magnesium, manganese, sodium, and calcium.

The major mineral here is potassium and manganese. Manganese as elaborated before is required for growth and development and sustains metabolic roles.

Potassium (K) is an essential nutrient for plant growth. It’s classified as a macronutrient because plants take up large quantities of K during their life cycle.

Potassium is associated with the movement of water, nutrients, and carbohydrates in plant tissue.

It’s involved with enzyme activation within the plant, which affects protein, starch, and adenosine triphosphate (ATP) production. The production of ATP can regulate the rate of photosynthesis.

Typical symptoms of potassium deficiency in plants include brown scorching and curling of leaf tips as well as chlorosis (yellowing) between leaf veins. Purple spots may also appear on the leaf undersides.

How to Make Starch Water for Plants

Starch water from Boiling

Rice and Pasta

The water from cooking pasta and rice when is usually strained out and removed. There is little preparation afterward as a good amount of starch has already been leached into the water which can be cooled, diluted, and applied to plants.

Fruit and Vegetable Peels

Use this method to obtain starch water from boiling fruits and vegetable peels. The amount of peels to use depends on the amount you have available at the time.

  1. Place the peels in a cooking pot
  2. Pour water and cover 1 inch above the peels
  3. Stir properly
  4. Place on medium heat (350 oF)
  5. Allow boiling for 30 – 45 minutes
  6. Strain the peels and save the water residue

If the resulting residue is too thick, you can also add water to thin it down for addition to your plants.

Starch water from Pulverizing 

Starch water obtained from pulverizing follows the same steps as from boiling (stated above).

The only difference is that the peels are broken up into small pieces in a blender before they are boiled.

This increases the surface area of the peels being exposed to boiling water. 

As a result, there is potentially a higher concentration of minerals that can be obtained from the peel using this method.

Starch Water from Soaking

Obtaining starch water from soaking requires removing the peels and leaving them in water for a period of time for the minerals from the peels to be leached into the water.


  1. Place approximately 200 grams of peels into a medium-sized jar
  2. Fill the jar with water 
  3. Cover the lid and seal the jar
  4. Allow to sit for 10 to 15 days

The peels will turn black as time passes and the water will also change color. After the time has passed, strain the water from the peels and apply to your plants.

Tip: Breaking the peels into smaller pieces will help speed up the soaking process.

How Long will Starch Water Last

Starch water will last a maximum of two days before it starts to ferment. This is because starches are organic compounds that oxidize and form into other alcohol compounds over time.

However, all is not lost. The alcoholic water produced can be used as an organic pesticide to ward off insects like gnats and moths.

Additionally, insects like fruit flies, gnats, plant lice, flea beetles, aphids, and other pests can be reduced using fermented pasta water as the alcohol from fermentation irritates these small insects which can also kill them.

The benefits of using fermented starch water have been proven to encourage a good bacterial population, promoting healthy root growth.

Using Cooking Water For Plants

The effects of cooking water on plants is attributed to the nutrient available in the pasta water when added.

The best cooking water is applied is before the crop has started its growth cycle. The growing period for crops, especially in the North American climate, spans from the beginning of spring to the end of fall.

During this time frame, plants are most active and require food and nutrients to carry about their biological activities, and pasta water can be an environmentally friendly and waste-free way to provide plants with the food they need to grow.

What are the Precautions When Using Starch Water

When using pasta water in the soil, you should always ensure that the water is at ambient or room temperature so that it does not kill the bacteria in the soil and harm the plant. This precaution is applicable if you are using the water from boiled pasta.

Additionally, pasta water is a good additive to soil, but care must be taken when watering as it can be easy to overwater the soil, leading to root rot and yellowing of the plant leaves.

Salt is also a concern when using any type of water from the kitchen to water plants, and you should be careful of the salts present in the cooking water.

Salinity affects plant, crop, and tree production by interfering with nitrogen uptake, reducing growth, and stopping plant reproduction.

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