Did you ever enjoy a beautiful planter arrangement or a hanging basket that you bought and after a month or so the lush flowering vanished? Despite dutifully watering new flowers were scarce. Then you fertilized, and maybe new leaves came up but not many flowers.
Did you use the right fertilizer? The middle number on the bag or bottle should be higher than the ones right and left of it. It shows the amount of phosphorus by weight.
Not all fertilizers contain phosphorus. Many are designed to target specific nutrient deficiencies, soil conditions, or growth requirements instead. Printed on the front of the bag or bottle, the N-P-K tells us what percentage, by weight, of each element is present. It’s the P value to watch if you’re hunting a high phosphorus fertilizer. The middle number should be higher if you aim for more blooms.
Too much nitrogen can result in lush, green growth but also reduce flowering.
Too little phosphorus can also be the cause of plants not flowering.
Why Use High Phosphorus Fertilizers?
Phosphorus is a key element in plant growth, and one that’s removed from the garden every time we mow, discard autumn leaves, or harvest our delicious crops. In order to keep on growing, we need to replace what we take away. Phosphorus makes up about 0.1% of the Earth's crust. Fertilizers that contain phosphorus are often sourced directly from plant or animal waste. Others are chemical, taken from mined rock phosphates.
Bone Meal: Bone meal is exactly what you’d imagine – ground-up bones. The bones are sourced from slaughterhouses, heat treated to kill pathogens, then milled into a fine, usable powder.
Fish Emulsion:
A more complex product than fish meal, fish emulsion is a liquified and chemically stabilized by-product of the seafood industry. Besides the excellent amount of phosphorus it provides, it contains a modest but balanced amount of nitrogen and potassium. Ratios vary from product to product but typically hover around 2-4-1. Fish emulsions also contain micro-nutrients like calcium, magnesium, and sulfur, as well as protein to help encourage the growth of healthy micro-organisms in the soil. While potted plants love fish emulsion, it’s often not a good choice for indoor plants because the smell tends to permeate the whole house or office!
Nitrogen - Phosphorus - Pottasium
When purchasing a fertilizer consider the N-P-K ratio of the product. Printed on the front of the bag or bottle, the NPK tells you what percentage, by weight, of each element is present.
High Phosphorus Fertilizers
Fertilizer Type % Nitrogen (N) % Phosphorus (P) % Potassium (K)
Rate of release:
Ammonium Phosphate 12 20 None Moderate to rapid
Rock Phosphate None 17-30 None Very slow
Bone Meal 4 10 None Moderate
Fish Emulsion 2-5 2-4 1-2 Rapid
Compost 1.5-3.5 0.5-1 1-2 Slow
Source: University of Colorado
For Flowering Annuals
It is a good idea to provide your flowering annuals with a bit of extra phosphorus as the growing season kicks off.- and also in the middle of the season. It’s a lot of hard work to grow an entire plant in a single season, and then produce flowers on top of that! Hydrangeas, Azaleas, Rhododendron, and Begonias also enjoy a bit of extra phosphorus as the summer sets in, to feed those luscious flowers. Herbs and citrus trees also benefit from a supplementary dose too.
Bone meal increases phosphorus in soil for optimal spring gardening results. Essential in the development of strong root systems, this element is released into the soil for up to four months. Slow, steady delivery of nutrients helps you grow plenty of big, blooming flowers, fruits, and vegetables.
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