What's in our compost and how do you use it?
Updated: Dec 6, 2022
When it comes to our compost, a little goes a long way. Our unique recipe, using your food waste, is not like other composts made from just green waste. Our compost is high in available nutrients and has a different proportion of these nutrients than other composts.
Each year we have our compost tested and the results have been impressive. Our finished compost has produced an average NPK of
3 - 1.6 - 2.18 + 4.5% Calcium
So what does this mean?
NPK stands for Nitrogen, Phosphorus and Potassium (once known as Kalium). They are just three of the macronutrients (or nutrients needed in great amounts) that plants need to grow. Plants also need calcium, sulfur, magnesium, carbon and oxygen. There are also micronutrients (still important but needed in lower amounts) and these are iron, boron, chlorine, copper, and nickel, just to name a few.
So, let's break down some of the reasons plants need this NPK and other macronutrients.
Nitrogen (N): Nitrogen is important in young plants for growth and among many things, a key component in chlorophyll (the part that makes plants green or C55H72MgN4O5). Without chlorophyll you will see your plants turn yellow. Our compost has an average of 3% total nitrogen (on a dry weight basis). The average N for compost is between 0.75-2.5%. We have readily available nitrogen as well as organic forms of nitrogen that will be released to your plants over multiple years.
Phosphorus (P): Phosphorus is crucial in adenosine triphosphate (ATP), which produce lots of energy when their bonds are broken. It gives a plant energy for root, seed and fruit development. This nutrient is becoming more scarce with estimates that mineable supplies can only support our crops for another 40 years. Our compost has an average of 1.6% phosphorus (on a dry weight basis).
Potassium (K): Potassium is a regulating chemical with responsibilities for movement of water in and out of cells. Wilting can occur in plants if they are deficient in potassium. Potassium is important for disease resistance, stem growth, and the taste and color of fruit and vegetables. Our compost has an average of 2.18% potassium (on a dry weight basis).
Calcium (Ca): Calcium makes up plant cell walls and is important to cell division. Deficiencies can be seen in the growing regions of roots, shoots and young leaves. Calcium can be low in highly weathered soils and have a low pH (acidic). Much of Kauai has Ca-leached oxisol soils.
Labeling the NPK on fertilizers is the standard. However, when it comes to compost it is much more difficult to label the NPK because it is much more unpredictable due to the varying feedstocks (materials we use to make compost) and processing environments. This is why I wanted to share our average from our last three analyses.
Now that you have a little more background on the nutrients we can explain how to use our compost.
Plant species, plant stage (seedling, mature, etc.), forms of nutrients in the compost, and what is used to create the compost can vary. So the amount of compost you should use for improved plant growth can VARY and DEPENDS.
Some will recommend, ½ cup per planting hole, 1/10 of a pound per square foot, 1 tablespoon per transplant hole, 3 tablespoons per container, or 50:50 blend (soil:compost).
And we are here to say, it all DEPENDS.
It is hard to say the EXACT amount to use but we can share some advice and suggestions to help you with ours.
So we did a little experiment to test our compost and see just how much (or how LITTLE) is needed to make a difference.
We used bokchoy seeds (three in each pot) with ProMix potting soil and
1 tablespoon of CK compost,
organic powder fertilizer,
1 teaspoon of CK compost,
¼ cup CK compost,
and no compost (control).
Check out our results. With just as little as 1 teaspoon you can see a difference in the seed germination and seedling growth compared to the control and even the organic fertilizer. After 20 days you can just how big the bokchoy were able to get with compost compared to their control treatment siblings.
Here is a chart with suggestions to help you use your CK compost fertilizer most efficiently. One gallon of compost fertilizer will cover 32 square feet or a 4’x8’ garden.
We encourage you to experiment yourself and observe how your soil and plants react to the compost . Use a control (plant with no compost) and add compost to other similar plants (in various amounts or all the same).
Experiment: label the treatments, take photos and share. We would love to see them!
Did the smallest amount make your seedlings grow better?
Did a large make them grow better
Did you notice any changes in the soil?
Were there more worms/critters in the soil after you applied compost?