Step 2: Add Kratky water and nutrients

Water first

Kratky nutrients are what turn plain water into a complete feed for your plant.

Use clean water. Fill the container up to the bottom of the net pot.

Nutrients

Plants need their food in the water. Use a hydroponic nutrient made for this method and follow the label exactly.

Why the nutrients go in the water

In a garden bed, roots find nutrients in the soil. In a Kratky container there is no soil, so everything has to be in the water. Plants need nitrogen for leafy growth, phosphorus for roots, potassium for overall health, plus smaller amounts of calcium, magnesium, iron and other trace elements. A hydroponic nutrient contains all of them.

Hydroponic nutrients are different

Fertilizer made for soil is not the same. It relies on soil life to break it down, and it can be missing elements a water-grown plant needs. Always use a nutrient labeled for hydroponics. Some are liquid and some are powder. Some come in two or three parts that are mixed into the water separately. Read the label and follow it exactly.

How much water?

Fill the container until the water just touches the bottom of the net pot. The damp growing medium then keeps the young roots moist, and the plant can start feeding right away. Do not fill it so high that the stem sits in water: the stem and leaves need to stay dry.

Use clean water

Tap water is fine in most homes. Some growers let it stand overnight first. Rainwater or filtered water also works. Avoid water from a salt-based softener, because the sodium can harm plants, and never use pond or puddle water, which may carry algae or pathogens.

What is pH?

pH measures how acidic or alkaline the water is. Plants can only take up their nutrients when the pH is in the right range, and leafy greens generally prefer slightly acidic water. Check it with a pH meter or test drops, and adjust it with the product recommended on the nutrient label. More on Nutrients, pH and Safety.

Do not exceed the label strength

More is not better. Too strong a solution can burn the roots and brown the leaf tips. Use the label rate for young plants. If the label gives separate rates for seedlings and mature plants, start with the seedling rate.

Mixing it the right way

Measure the nutrient with a measuring spoon or cup, add it to the water and stir well. If it comes in more than one part, add each part to the water separately and stir in between. Never pour the concentrates straight into each other. Mix into the full volume of water, either before filling the container or in the container itself if it is big enough to stir.

Keep a little extra

Some growers mix a little extra solution in a clean, labeled bottle for topping up later. Store it somewhere cool and dark, out of reach of children and pets, and never in a drink bottle that could be mistaken for something to drink. Write the date on it.

Water and nutrient checklist

• Clean container, washed and rinsed
• Clean water, not softened or from a pond
• Hydroponic nutrient, measured to the label
• pH checked and adjusted
• Water just touching the bottom of the net pot

When to change the water

In the Kratky method you usually do not change the water. The plant drinks it down, and that is how the air gap forms. Only change it if it smells bad, turns cloudy or slimy, or you decide a fresh start is needed.

Next step

With the water and nutrients ready, put the lid on, set the net pot in the hole and turn to Step 3: Plant a seedling.

Water temperature

Cool-to-room-temperature water is best. Very cold water slows root growth, and warm water holds less oxygen and encourages root rot. Let water that is very cold from the tap come to room temperature before you mix the nutrients.

Measuring accurately

Small containers need small amounts of nutrient, so accuracy matters. Use proper measuring spoons, not kitchen guesswork, and work out the amount for the volume of water you actually have. Writing the amount on the container saves you working it out again when you top up.