If a plant is to reach its full potential, it must be provided with specific nutrients at various times throughout its life cycle. Plants grown outdoors and in soil rely on the soil’s microorganism to break down organic matter into usable nutrients. Even a high-quality soil with a wide range of ingredients may not be able to supply a plant in its blooming or ripening stage with the optimal ratio of nutrients required for maximized flower and essential oil production. This is why many outdoor growers amend the soil during the blooming stage with either dry ingredients, which contain the elements that enhance blooming, or liquid additives designed to do the same.

Read also: Build the Best Organic Soil for Your Growroom

Although chemical fertilizers and additives can be used in an outdoor garden, many outdoor growers prefer organic or organic-based additives to boost the final stages of growth. Organic additives enable the soil to continue functioning as a living soil and embrace the power of beneficial microorganisms.


Gardener fertilizing their garden with bio-granular fertilizer.Granular fertilizer - Simon Kadula/Shutterstock

Top Dressing

Top dressing is amending a soil by adding various dry fertilizers to the surface around the base of the plants. As the plants are watered, via rain or an irrigation system, the water-soluble nutrients become available to the plants. As time goes by, the organic material on the surface is broken down further by beneficial microorganisms and even more nutrients become available to the plant. In order to ensure a plant receives the appropriate amount of nutrients specific to blooming, a grower may choose to top dress his or her soil at the beginning or in the middle of the blooming stage. It should be noted that the majority of the nutrition provided by top dressing is not instantaneous, so some forethought must be used when top dressing. If a grower wishes to boost the final stages of blooming, it is necessary to top dress a few weeks before that stage begins so the organic material has some time to break down and become available.

For example, during an outdoor plant’s blooming stage, a grower can top dress the soil with high phosphorus bat or seabird guano. As it rains or the grower waters the plants, the guano will provide a boost of phosphorus and microorganisms to the plants. The added phosphorus will help stimulate the flowering process and the microorganisms will increase nutrient uptake. Plants that are given a boost of phosphorus, potassium, calcium, and microorganisms in the later stages of blooming will produce denser flowers and an increased amount of essential oils.

Read also: Strengthening Plant Roots with Phosphorus and Potassium

There are many different organic dry ingredients available to use as a top dressing for outdoor plants. When discussing top dressing or amending a soil for the later blooming stages, the most effective ingredients are those that contain very little or no nitrogen. Supplying blooming plants with too much nitrogen will inhibit large flower production. Organic ingredients with higher ratios of phosphorus, potassium, and calcium are best suited for top dressing a garden in the blooming stage. Due to the relatively fast availability of nutrients, the following are some of the most popular top-dressing ingredients used by outdoor growers:

Top Dressing Ingredients for Adding Phosphorus (P)

Bat Guano (High Phosphorus) — High-phosphorus bat guano is an old favorite of outdoor growers and an excellent source of phosphorus. Bat guano is known to not only increase flower sets, but also their size, aroma, and flavor. Many types of high-phosphorus bat guano contain a good amount of calcium too. Make sure the bat guano you purchase is ethically sourced.

Bone Meal Bone meal is an excellent source of readily available phosphorus; revered for its ability to promote strong root development. Bone meal is also a great source of calcium.

Fish Bone Meal — Fish bone meal is essentially the same as bone meal, except it is derived from fish. A great source of both phosphorus and calcium.

Seabird Guano — Seabird guano, like bat guano, is known to increase the amount of flower/fruit sets and their size. An excellent source of phosphorus and micronutrients. Seabird guano also contains a wide variety of microbial life.

Read also: The Science Behind Bone Meal


Top Dressing Ingredients for Adding Potassium (K)

Kelp MealKelp meal is a source of readily available potassium and a variety of micronutrients and plant hormones. This great soil additive can also increase overall plant health and vigor. Kelp meal should be used as an ingredient in the original soil mix. It can also be used sparingly as a top-dressing during blooming. Due to its high plant hormone content, too much kelp in the later stages of blooming could potentially trigger a growth spurt, leading to spindly flower development.

Langbeinite — Langbeinite (sold under many different brand names) is a naturally occurring mineral and is water soluble. A good source of potassium, sulfur, and magnesium.


Gardener mixing dolomitic limestone powder in garden soilDolomite lime powder - FotoHelin/Shutterstock

Top Dressing Ingredients for Adding Calcium (Ca):

Oyster Shell — Oyster shell is an excellent organic source of calcium that will accelerate root development and, in turn, improve nutrient uptake. Oyster shell also works as a pH buffer, keeping the soil from becoming overly acidic.

Dolomite Lime (Sweet Lime) — A rich source of calcium and magnesium. Dolomite lime is also a great pH buffer for any soil composition and, as with oyster shell, ensures the soil’s pH doesn’t turn too acidic.

It should be mentioned that calcium is imperative for all stages of plant growth and should be incorporated into the vegetative as well as the blooming stage of growth. Calcium is relatively slow to release so it is important to be proactive with dry calcium ingredients in the soil or as a top dress.


Grower applying compost tea to their garden.Compost tea - Vasilii Kosarev/Shutterstock

Compost Teas

For outdoor growers who do not want to amend the soil via top dressing, there are alternative methods to provide plants with the specific nutrients to boost flower and essential oil production. An organic tea, brewed from any of the previously mentioned dry top-dressing ingredients, can be a very effective way to deliver stage-specific nutrition to an outdoor garden. Teas are generally brewed in a specific tea brewer or other homemade device that combines water, oxygen, and the organic matter for a period of time. When brewed correctly, these teas will not only contain essential elements, but also an abundance of microbial life. Guano teas, especially teas made from high-phosphorus bat or seabird guano, are great additives for the blooming and early ripening stages. Guano teas supplemented during ripening will help increase bloom density and stimulate essential oil production.

Read also: Care for a Cup of Compost Tea? Your Plants Will!

Other Organic-Based Liquid Additives

Liquid Kelp Extracts — Although kelp was once rarely used as a bloom booster, some of the kelp formulations available today are specifically designed to do just that. When harvested at the correct time or in a particular manner, kelp extract can contain a variety of hormones that trigger flowering and ripening. Kelp also contains a high amount of trace elements that are beneficial in the fruiting/flowering stage. Kelp extracts specific to bloom stimulation will encourage rapid cell division during flowering and increase the production of specialized sugars found in fruit or flowers.

Liquid Amino Acid Formulas (Protein Hydrolysate and Enzymes) — Organic products that contain high concentrations of amino acids are great to supplement during the blooming and ripening stage. Protein hydrolysate is essentially organic matter (usually soy protein) broken down into the essential L-amino acids. Amino acids are the building blocks of the proteins and enzymes which directly influence the structure and metabolism of plants. Supplementing a protein hydrolysate during the blooming period will enhance the utilization of other nutrients, boost the plant’s immune system, increase plant respiration, and reduce stress. Protein hydrolysate is a multifaceted additive that increases fruit/flower production in many different ways. This means all the natural functions that occur during ripening (bloom density, essential oil production, etc.) will be accentuated. Amino acids also help build the plant’s defenses against various pathogens. Isolated enzyme formulas are also available and provide specific benefits to plants, such as root, flower, or essential oil stimulation.

Read also: 4 Benefits of Amino Acids in the Garden

Liquid Carbohydrate Formulas — Supplementing a liquid carbohydrate formula during the entire blooming stage is advantageous but is especially so during the late blooming/ripening stage. Carbohydrates provide food for the beneficial microorganisms in the soil, which, in turn, help all plant functions. Increased carbohydrates have also been shown to stimulate essential oil production in many varieties of plants. Adding carbohydrates during the ripening stage will dramatically boost the final production of essential oils, leading to better aromas and flavors.

Outdoor growers are always on the hunt for ways to maximize flower and essential oil production. Although it is the vegetative and early flowering stages that provide the foundation for a successful ripening and harvest, the later stages of blooming is when the majority of the magic happens. A good organic living soil will provide adequate nutrition throughout the entire life cycle of the plant. However, implementing top dressing or liquid additives in the blooming stage can provide the enhanced nutrition needed to maximize flower and essential oil production. By amending a soil by top-dressing organic dry ingredients or by using a liquid tea or extract, an outdoor grower can rest assured that he or she has done everything in his or her power to provide optimal nutrition for the final weeks of blooming.