Are Water Grown Plants Really "Carefree"?

Just like plants in soil, plants in water need nutrients. There is a huge misconception and a lot of misinformation about the delivery of those nutrients to plants growing in water.  The nutrients must be water soluble in an available form the plants can readily use.  When plants are grown in soil, microbes living in the soil do all of the work breaking down and processing the nutrients for the plants to use. That does not happen in water.  A great example of this is "banana water". While banana water can be a good amendment to plants in soil, it will cause accelerated rot to plants in water because it is just banana gunk sitting in the water growing harmful bacteria and fungus, while also attracting bugs.

The same with oxygen! Even though plants produce oxygen during photosynthesis, they still need to take in oxygen — especially at night when photosynthesis stops but respiration continues. Plants uptake oxygen primarily through diffusion via small openings in their tissues in leaves and stems, but also through roots. Roots take in oxygen from the surrounding soil via tiny root hairs. This is critical for aerobic respiration, which helps roots generate energy for growth. In soil, the microbes and even tiny beneficial insects such as springtails most people never see, aerate the soil constantly replenishing oxygen for the plant. In water, that does not happen so the plants use up all of the oxygen in water quickly. Each time you top off or change the water, you are adding more oxygen for the plant, but it is likely not enough. 

Adding a small amount of hydrogen peroxide (H₂O₂) to water can help plants growing in water get more oxygen without harming them, as long as it's used correctly.

How It Works:

• Hydrogen peroxide breaks down into water (H₂O) and oxygen (O₂), releasing extra oxygen into the water.
• This improves oxygen availability for the roots, which can prevent root rot and promote healthier growth.

How Much to Use:

For hydroponic or water-grown plants, a safe dilution is:

• 3% hydrogen peroxide (the kind from a pharmacy): 1 teaspoon per gallon (about 5 mL per 4 liters) of water
• Food-grade 35% hydrogen peroxide (stronger concentration): 1 teaspoon per 10 gallons (about 5 mL per 40 liters) of water.

Benefits:

✔️ Prevents root rot by reducing anaerobic bacteria and fungi
✔️ Increases oxygen levels for healthier root development
✔️ Helps break down organic matter and keeps the water cleaner

Precautions:

• Don’t overdo it! Too much can damage roots.
• Dilute properly before adding to the water.
• Use fresh water and reapply every few days, as H₂O₂ breaks down quickly.

One of the biggest and most overlooked issues relating to plants growing in water is dehydration, which would naturally seem counterintuitive. How can something sitting in a container of water become dehydrated? Even though plants growing in water have constant access to moisture at their roots, they can still suffer from low humidity because plants lose water through their leaves via transpiration. Here’s why:

1. Water Uptake vs. Water Loss

   • Plants absorb water through their roots, but they lose moisture through their leaves.
   • In low humidity environments, water evaporates more quickly from the leaves than the roots can replace it, leading to dehydration of leaf tissues.

2. Stomatal Behavior

   • Plants have stomata (tiny pores on their leaves) that regulate water loss.
   • When humidity is low, these stomata stay open longer, increasing water loss.
   • Even though the roots have water, the leaves can still dry out faster than they can replenish moisture.

3. Lack of Internal Transport Adjustments

   • Some plants rely on soil to regulate moisture absorption. When grown in water, they may not efficiently regulate water movement to compensate for high transpiration.

4. Dry Air and Leaf Stress

   • Air movement (fans, HVAC, open windows) can increase water loss, drying out leaves.
   • Plants adapted to humid environments (e.g., tropical plants) struggle in dry air even when their roots are submerged.

How to Prevent Humidity Issues in Water-Grown Plants

• Increase humidity with a humidifier. Contrary to popular belief, a "pebble tray" is not enough.
• Mist leaves occasionally (unless the plant is sensitive to wet foliage). This alone is also not helpful enough, even for plants living in soil, but many plants still do well and benefit from misting.
• Avoid strong air currents that dry out leaves.
• Use a humidity dome or enclosure for extra sensitive plants.

So, even though roots are in water, leaf dehydration can still be a major issue if the surrounding air is too dry!

Growing plants in water does reduce some pest issues but doesn’t make them pest-free. Here are some common pest concerns and how to deal with them:

1. Fungus Gnats

   • Problem: These tiny flies lay eggs in moist environments, and their larvae feed on plant roots.
   • Prevention:
     • Add a layer of sand or small pebbles to the water surface to prevent egg-laying.
     • Use hydrogen peroxide (H₂O₂) treatment (1 tsp per gallon of water) to kill larvae.
     • Introduce beneficial nematodes (Steinernema feltiae) to control larvae naturally.

2. Algae Growth (Attracts Pests)

   • Problem: Green or brown algae in the water can attract pests and deplete oxygen.
   • Prevention:
     • Keep the container out of direct sunlight or use opaque/amber containers.
     • Change the water weekly to reduce nutrient buildup.
     • Add a few drops of hydrogen peroxide or an aquarium air stone for oxygenation.

3. Mosquito Larvae

   • Problem: Stagnant water in large containers can attract mosquitoes.
   • Prevention:
     • Use Mosquito Dunks (Bti bacteria) to kill larvae.
     • Agitate the water with an air pump or change it frequently.

4. Aphids & Mealybugs (On Leaves)

   • Problem: These pests can infest stems and leaves, sucking plant juices.
   • Prevention:
     • Wipe leaves with a diluted neem oil or insecticidal soap solution.
     • Introduce ladybugs or use a strong water spray to dislodge them.

5. Root Rot (Caused by Bacteria & Fungi)

   • Problem: If oxygen is low, roots can decay and attract fungus gnats.
   • Prevention:
     • Use oxygenating additives like hydrogen peroxide (H₂O₂) or an air pump.
     • Remove decaying plant matter to prevent bacterial buildup.

Please do not let any of the above scare you away from growing plants in water. It is super cool to watch them grow and thrive in water, but as you can see, it is not quite as "maintenance free" as you may have been led to believe.