How to Use Organic Nutrients in Your Indoor Garden

These tips help you grow healthy, productive hydroponic plants with natural fertilizers.


Look at the label on any package of plant fertilizer and you’ll see its N-P-K ratio. The letters refer to nitrogen (N), phosphorus (P), and potassium (K), which are the key macronutrients that plants need to grow. The ratios are presented with numbers, such as 5-1-1 or 2-5-5. As plants grow from seedlings to leafy mature plants to flowering plants, their nutrient requirements change. Plant fertilizers come in different formulas—with varying N-P-K ratios—so you can feed your crop exactly the nutrients it needs throughout its life cycle.

Most plant foods have the three nutrients, but the source of the nutrients has a significant impact on the health of your plants. Organic fertilizers are made with natural ingredients, such as fish and seaweed, while synthetic plant food is manufactured with chemicals, such as ammonium nitrate or urea. Think about the difference between eating processed foods and whole foods. Both have protein and carbohydrates, but whole foods are healthier for you because the nutrients come in forms that are better for your body. The same is true of organic fertilizers and your plants.

While growing healthy plants that flower abundantly indoors is easy and convenient with liquid organic fertilizers, you’ll want to remember these tips to get the best results.

Be patient for growth. Plants fed with organic fertilizers don’t show the dramatic, fast growth that you might get from synthetics, but at maturity they are robust and flower abundantly. Be sure to follow your fertilizer’s recommended dilution rates and feeding schedules—excess nutrients don’t make plants grow faster or bigger, and they can even harm your crop.

Use any system. The beneficial microbes that break down natural fertilizers into nutrients readily absorbed by plants flourish in soil, so organic fertilizers are especially well suited to crops grown in biologically active dirt. However, liquid organic fertilizers are very effective in hydroponic systems or any indoor growing setup as well. Thoroughly mix the fertilizer with water to dissolve it completely, so it can flow smoothly through any tubing you’re using.

Check the pH. The acidity versus alkalinity (the pH) of your nutrient solution (fertilizer plus water) is critical to your plants’ capacity to absorb the phosphorus, potassium, and other trace elements in it. For most indoor garden crops, the ideal pH is slightly acidic, between 5.5 and 6.5. Organic fertilizers are close to neutral (7), but synthetics are high in salt, which can lower the pH of your solution. You can buy an accurate, simple-to-use pH meter for less than $30. Use it every time you mix a batch of nutrient solution.

Mix with distilled water. Chlorine, often used to treat municipal water supplies, can kill those beneficial microbes that help turn fertilizer into nutrients for plants. Well water is often high in minerals, which can raise the pH of a nutrient solution. Distilled water is pure, pH neutral, and best for blending with your organic fertilizer.

Make it fresh. When exposed to oxygen and water, the beneficial microbes in organic fertilizer begin breaking down the ingredients into nutrients. As soon as a day later, competing bad bacteria may move in and diminish the effectiveness of your nutrient solution. Prepare each batch just before using it so that it’s fresh and at its peak. Keep a lid on the reservoir to discourage unwelcome bacteria from colonizing there.

Clean the scene. Even tiny spills of liquid fertilizer can become hosts to destructive fungus in your grow room and attract fungus gnats. Be sure to keep the area where you mix and use organic fertilizer spotless. Avoid using the lid of a fertilizer container to measure, even if the cap has measurements on it, so that you don’t accidentally adulterate the fertilizer still in the container. If you have done that inadvertently, you may notice a white brittle substance around the edges of the cap. Remove it with a clean cloth and rinse the lid clean.

Know the scent. The aroma of concentrated organic fertilizer made from fish can be strong before you dilute it, and it may even draw the attention of any cats in the house. But if that tempts you to switch to synthetics, you might want to take a whiff of ammonia first and then decide which scent is more unappealing.