Why do plants need phosphorus?

+29 votes
asked Oct 19, 2018 in Home & Garden by Gemma (820 points)
edited Feb 20, 2019 by Kris
The strawberry plants I planted last year aren’t doing well. The plants are small and have very few blossoms. A neighbor suggested they need more phosphorous. Why do plants need phosphorus and how do I go about adding more to my soil?

3 Answers

+21 votes
answered Dec 17, 2018 by Diana (630 points)
edited Dec 31, 2018
It sounds like your neighbor has probably made the right diagnosis. Your plants are showing classic symptoms of a phosphorous deficiency.

Plants need phosphorous to help them convert other nutrients into usable forms that help them grow. If you look at a bag of fertilizer, you’ll usually see a NPK balance list. The P stands for phosphorus, the N for nitrogen, and the K for potash, a source of potassium. These three elements are essential for healthy plant growth. When the plants aren’t getting enough phosphorous there roots don’t grow strong, blossoming is poor, and the plants do not produce quality fruits.

There is no way to have healthy, productive plants if they suffer from phosphorus deficiency. Phosphorous is essential to healthy, productive plants, especially when you are growing a fruit like strawberries that is naturally high in phosphorous.
+9 votes
answered Mar 25, 2019 by ryann (1,020 points)
edited Jul 1, 2019 by Kris
As to your first question why do plants need phosphorus, I agree with Kris. Plants need phosphorus because it helps them convert nutrients into the building blocks they need to grow. This is how they make the food they absorb into something useful.

As to your second question, I think you can try these methods:

One way to enrich phosphorous levels is with chemical fertilizers. If you choose to go this route looks for a fertilizer with a high P count. For instance, if the bag says it has a fertilizer rating of 10-10-10 then it has equal amounts of nitrogen, phosphorus, and potassium. If, however, it reads 10-15-10 it contains more phosphorus than it does the other two nutrients. Phosphorus is always the second number.

You may also use organic methods to increase the phosphorus level. Sometimes just adding compost to the soil is enough to help the roots take in more of the available phosphorus but if not, try working in some rock phosphate or bone meal around each plant.

You do want to be careful not to overdo the phosphorus, though. Not because it will damage the plants. It’s almost impossible to give a plant too much phosphorus. Excess phosphorus is a major pollutant, however, and excess will run off into the water supply.
+2 votes
answered Oct 26, 2018 by FRANK (580 points)
edited Feb 12, 2019
I know exactly why do plants need phosphorus, because phosphorus is important for cell division and the development of new tissue in plants. So adding phosphorus to soil aids root growth, hardiness, and often quickens maturity in plants. It’s easier to tell if you have a phosphorus deficiency in the soil by the appearance of your plants than how well they grow or how much they produce. Plants that are extremely lacking in phosphorus will have stunted growth because they need this chemical in order to grow, but they will also appear more dark green in color. If sugars build up from a lack of phosphorus, the plants can take on a reddish-purple color that is abnormal. These are only signs of extreme deficiencies in the soil that require adding phosphorus to the soil, but your plants can benefit from additional phosphorus even if they don’t look like they need it.
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