Types of fertilizers we like

    Prior to human colonization, all the Hawaiian Islands were populated by millions of seabirds. Today, these large populations are almost entirely restricted to the Northwestern Hawaiian Islands and offshore islets of the main Hawaiian Islands, with a few exceptions like Kīlauea Point, Kaua‘i, and Ka‘ena Point, O‘ahu. Many botanists believe the droppings from these seabirds, combined with those of the native Hawaiian forest birds, which were much more numerous in the past, resulted in a constant and significant transport of plant nutrients (e.g., nitrogen, potassium, phosphorus) from the ocean to the land. Additionally, the newly-formed basalt (e.g., lava, cinder) that makes up the primary substrate of the Islands, particularly the newer islands like Maui and Hawai‘i, also contains important plant nutrients like iron and magnesium.

    Today, things are quite different. Both the seabirds and native forest birds are largely gone, and with them, the transport of plant nutrients into the interior of the main Hawaiian Islands. Thus, we, as native Hawaiian plant enthusiasts, have an important horticultural question: "How critical was/is this nutrient flow to the growth and ecology of native Hawaiian plants?" We don't think there is a definitive answer yet to this question. Therefore, the use of fertilizers with native Hawaiian plants will be a case-by-case experiment for us all for some time to come. With this said, here is what we know and have learned about fertilizing native Hawaiian plants. 

    Native Hawaiian plants require nutrients like any other plant. Attention is especially needed for plants grown in containers as their final home (e.g., Brighamia spp.). Containers may also be used as temporary homes for plants until they attain the size needed to plant them out at a permanent site (in a garden or landscape) and will, therefore, require nutrients while in the container. Once planted in the ground, new plantings may initially benefit from fertilization, but often require little, if any, additional fertilizers once established. This is because the fallen leaves, flowers, fruits, twigs, and branches decompose to form a natural mulch and recycled fertilizer if left on the ground. The problem arises when these natural materials are gathered and removed, usually for aesthetic reasons. See Soils & Media under Native Soils and the benefits of using them.

    A balanced fertilizer contains the three primary elements, nitrogen (N), phosphorus (P), and potassium (K), as well as other macronutrients and micronutrients essential for a plant's health and vigor. Fertilizer also provides microorganisms in the soil or media with the chemicals they need. Together, the result is healthy and vigorous plants with vibrant foliage, strong roots, colorful flowers, and well-developed fruits.

    Macronutrients such as nitrogen, phosphorus, potassium, calcium, sulfur, and magnesium are the essential elements needed in large quantities for fundamental processes such as building cells and proteins, energy transfer, and regulating water balance. They also play key roles in chlorophyll structure, photosynthesis, enzyme activation, and the development of roots, shoots, flowers, and fruits. In contrast, micronutrients such as manganese, boron, chlorine, iron, zinc, copper, and molybdenum are essential elements needed in smaller quantities. They are essential for enzyme activation, photosynthesis and respiration, other metabolic processes like amino acid synthesis, and overall growth and development.

    There are two general types of fertilizers to consider using for native Hawaiian plants, organic and inorganic, with each type having specific characteristics and applications.

Organic: Unfortunately, in recent times, the term "organic" has become ill-defined and misused. (In science, "organic" is defined as any carbon-based chemical that originated from a living organism.) Here, we define "organic fertilizers" as those fertilizers derived from (once) living organisms.

Inorganic: In science, "inorganic" is defined as any chemical that originated from a non-living (i.e., non-organism) source; they are typically made synthetically or are geologically extracted (e.g., iron ore from a mine). "Inorganic fertilizers" are typically small molecules like magnesium sulfate that contain elements important for plant growth. 

    There are several organic fertilizers commonly available from garden shops or online. Here are the types we have used: 


    There are some "organic" inorganic fertilizers available at garden shops or online that are not technically organic but are often used by organic farmers and horticulturists. Here are the types we have used:


    There are several inorganic fertilizers commonly available from garden shops or online. Because they are synthetic (i.e., man-made), these fertilizers can sometimes lack important macro- and micronutrients or have macronutrient mixtures that are inadequate or even possibly harmful to some plant species (e.g., high nitrogen fertilizers used on carnivorous plants). Here are the types we have used:


    Speaking generally for most native Hawaiian plants, we have found that most store-bought fertilizers should not be applied at the label's recommended full-strength, even if you don't see any adverse effects such as leaf or root burn, for two reasons: 

    In conclusion, less — not more — is usually best. We suggest providing your native Hawaiian plants with frequent but small doses of nutrients, perhaps at ¼ to ½ the label's recommended strength. As time goes by, you will naturally get to know your plants better and discover how to best apply fertilizers, just as you learn how to best water and light your plants. Also, we suggest foliar feeding (rather than always applying fertilizer to the soil or media) since this more closely mimics the ancient means that Hawai‘i's native birds (and bats) once supplied nutrients to our native flora.