Everyone wants a sustainable future to live in and we, as gardeners, tend to strive toward this goal in our own ways. There are always some choices that are better than others—certain lights are more energy efficient than others, a number of greenhouses allow us to use the sun’s energy to provide light and heat, and some growing mediums are reusable and sustainable. This article is going to focus on a different, yet related, area: organic, sustainable nutrients.

Seaweed and Kelp

One such organic sustainable nutrient is seaweed, including the large brown variety known as kelp. Seaweed and kelp grow in vast underwater forests and can be harvested from the ocean, grown naturally or farmed, or can be gathered off beaches as they inevitably wash ashore. Since seaweed is extremely fast growing and does not harm native species—in fact, many animals feed, live and raise their young in dense kelp forests—these underwater plants are ideal candidates for a sustainable source of organic nutrients for the indoor garden.

However, seaweed- and kelp-based organic nutrients are not only a great choice because of how environmentally friendly they are. They are also full of what plants need. While having insignificant NPK levels, kelp-based nutrients do contain over 70 essential vitamins, minerals, amino acids, trace elements and plant hormones.

This is what enables kelp to grow half a meter a day, reaching lengths exceeding 100ft. These fertilizers also contain natural antibiotic properties that can suppress harmful bacteria while promoting the growth of beneficial bacteria. Organic kelp-based fertilizers help facilitate the uptake of nutrients and can help relieve the stress in cuttings and plants after being transplanted.

It is possible to dry seaweed and kelp into meal that can be mixed into your growing medium. There are also many liquid forms of seaweed-based fertilizers that are water-soluble, which can easily be added to a hydroponic reservoir, hand watered into planters or foliar sprayed. A benefit to liquid kelp-based fertilizers is that they are assimilated by the plants immediately, while kelp and seaweed meal can take up to a month or more to be assimilated by plants.

Seabird Guano

Seabird guano is an organic nutrient that is sustainable and can be collected with minimal disturbance to the wildlife and ecosystem. Seabird guano—the droppings of fish-eating seabirds—is high in nitrogen, phosphorous and calcium, with an average NPK around 10-10-3. The best seabird guano comes from Chile and Peru, where the Humboldt Current along the coast keeps the rains away and prevents the decomposition of the guano.

Seabird guano is water-soluble and has little odor, and can be assimilated by plants in one to four months when applied in powder form. For use in hydroponic systems or for quicker assimilation, liquid seabird-guano-based fertilizers are recommended. Or, as a DIY project, you can wrap powdered seabird guano in a nylon stocking and soak it in a bucket for one to three days to make your own liquid fertilizer that won’t clog pumps or drippers in hydroponic garden systems.

Worm Castings

Worm castings—also known as vermicompost or worm humus—are the organic materials that have been digested by worms. Nutrient levels vary depending on what the worms have been fed, but there is usually some nitrogen and many trace elements. Worm castings are an excellent choice because it won’t reach toxic levels of nitrogen and burn plants.

They also promote healthy soil and beneficial bacteria and fungi. Worm castings should be used in conjunction with some other organic nutrient because vermicompost will help break it down, making the nutrients more easily assimilated by the plant. Worm castings can also be used to help soil/soil-less mediums retain more water. However, worm castings are dense and can cause the medium to have poor aeration, so be careful not to over apply.

Worm castings are an environmentally friendly option for an organic garden fertilizer because converting biowastes into a plant friendly nutrient reduces the waste that goes to landfills. Worm castings are more readily available to plants than regular compost, which can take years before it is safe to use in a garden. Worm castings are also a cost-effective solution for plant nutrients that could be utilized by poorer nations and regions where soil conditions are less than ideal.

Fish Emulsion

Fish emulsion is a soluble liquid fertilizer made of fish waste that has been heat and acid processed. It contains many micronutrients, has an average NPK of 4-1-1, and releases nutrients quite fast. Fish emulsion is beneficial for tender plants like seedlings and cuttings, and can be top-watered, used in a hydroponic solution or foliar sprayed. The only downside of fish emulsion is that is can smell pretty foul—even the brands that are “deodourized” can have a bad odor.

Fish emulsion is a great sustainable source of organic nutrients for plants. With fish stocks steadily depleting, fish farming is becoming more common and the run-off water from these farms is loaded with fish emulsion. Indeed, many fish farms are collecting the run-off water, processing it and selling to indoor and commercial gardeners.

Some farms are also turning to aquaponics to incorporate gardening into their system. Here, the run-off from the fish farms is pumped to greenhouses and hydroponic systems, providing plants with the nutrients they need to thrive.

You can make your own fish emulsion if you have a fish tank at home. Whenever the water in the tank needs replacing, just use it to water your plants.

Making Your Own Compost Tea

Another way to get a soluble organic fertilizer that is environmentally responsible is to make your own compost tea. By making it yourself, you can control exactly what is going into the substance. Some common ingredients are fish emulsion, soluble seaweed and/or kelp, molasses, worm castings, processed insect manure and seabird guano.

To make your own compost tea fill a nylon sock with your combination of water-soluble organic nutrients and soak them for a few days in a bucket filled with water for. The sock will filter out anything that might clog up pumps or drippers used in hydroponic systems. After a few days the compost tea will be ready to added to a hydroponic reservoir or diluted and top-watered.

Another way to make compost tea is to get an old drip coffee maker (you can easily find one at thrift shops and reuse stores). Insert a coffee filter, add your water-soluble organic nutrient mix into the filter and run water through the coffee maker, just as you would when making coffee. The nutrient will percolate through the filter and you will end up with a coffee pot full of compost tea.

A warning, however: Making your own compost tea can stink, so it might be best to create it in a shed, the garage or on a porch or balcony. Nutrient contents will also vary, so testing with an EC or PPM meter will help you dilute the solution to a plant-safe level.

Every choice we make has an effect on the world and those around us. There are consequences to our actions. Starting a garden is a step in the right direction, but we must always try to be better. Think of the where your plants’ nutrients come from and what effect harvesting or creating that nutrient might have on the ecosystem. Using organic nutrients from a sustainable source can make gardening that much more environmentally friendly and, gradually, lead to a better tomorrow.