Phosphorus vs. Potassium to Stimulate Flowers

Benefits of Phosphorus

• Phosphorus is the nutrient responsible for stimulating fast flowering and fruit development. This makes it the most important ingredient in a fertilizer intended to initiate blooming. Typically, you only need to apply extra phosphorus if a soil test shows that the soil doesn't have enough, but you can also apply it during the flowering season to perk up plants and encourage the development of new buds.

Potassium Effects

• Potassium is essential for overall plant health, but it doesn't stimulate blooming on its own. It aids root growth, plant metabolism and stress tolerance, keeping plants healthy enough to flower. It can also increase the size of fruits and nuts. These benefits don't directly affect flower growth, but potassium works well in tandem with the main bloom stimulator, phosphorus, acting as support and keeping roots strong during flowering.

Bloom-Booster Fertilizers

• Bloom-booster fertilizers include more phosphorus and potassium than nitrogen. This is because nitrogen promotes green growth, which can limit the development of flowers if it's the primary nutrient. An example of a bloom-booster formula is a 3-20-20 formula, which means it contains 3 percent nitrogen, 20 percent phosphorus and 20 percent potassium. You can use this type of fertilizer throughout the spring or summer flowering season.

Organic Sources

• Applying organic materials to your garden can also provide phosphorus and potassium. Some sources, such as manure, contain large amounts of nitrogen in addition to the ingredients that stimulate blooming and rooting, which means they're likely to green up your lawn and cause fast, leggy growth in other plants. However, bone meal contains 15 to 27 percent phosphorus with less than 7 percent nitrogen, making it an excellent choice for encouraging flowering. Wood ashes are a good source of potassium, but because they acidify the soil in large amounts, greensand is often a preferable choice that's slower to decompose into the soil.

Considerations

• Before you dump bloom-booster fertilizer on flowers, make sure your plants have enough green growth to support bud development. This means that an initial dose of nitrogen-rich fertilizer at the beginning of the growing season is key to future flowering and overall health. Most flowering plants do well with a balanced fertilizer -- such as a 20-20-20 blend -- to encourage healthy growing and blossoming. Large amounts of phosphorus and potassium are only necessary if your plants aren't flowering, if you want to speed the development of blossoms or if soil tests indicate a deficiency.