How To Add Phosphorus To Soil Organically - Growfully

Share this article:

• Facebook
• Pinterest43
• Email
• Print

Phosphorus is essential to good soil health—and crop health! Learn how to organically increase the amount of phosphorus in your soil here.

There are three macronutrients gardeners need to stay on top of—NPK, or nitrogen, potassium, and phosphorus—and while a lot of folks focus on nitrogen, it seems like phosphorus is never at the top of gardener’s minds.

We’re here to help teach you why phosphorus is something you need to stay on top of! Let’s get your levels in check.

What is the very best way to add phosphorus to my garden?

Looking for the quick and easy answer? No problem. We like adding either bonemeal or fish meal to our soil for a quick correction of soil P levels. Or, we use a kelp (AKA: seaweed) liquid foliar fertilizer.

Growfully Protip

Looking for a quick and easy cheat sheet with all of these possible phosphorus amendments? We have you covered.

Why do plants need phosphorus?

Whereas nitrogen is the main fuel for overall plant growth, phosphorus’s main goal is to help in the formation of new tissue. This manifests in a number of ways—from helping plants to grow a strong root system to helping your plants grow numerous side shoots, which can produce more fruits and veggies.

Phosphorus is also helpful in helping a plant weather variations in moisture and temperature (in particular, it helps plants be more cold hardy).

Signs of a phosphorus deficiency

Spotting a phosphorus deficiency can be tricky. Stunted growth and weak plants are signs that your soil needs more phosphorus, but if you don’t have healthy plants to compare to, this can be hard to pick up on early enough.

While stunted plant growth is the main sign, you may also notice your plants are dark green in color (both the leaves and the stems). Some may even show a reddish-purplish tint. Unfortunately, both of these symptoms can also be signs of other plant problems (or in some cases a perfectly healthy and normal characteristic of the plant variety you are growing).

Plants who are growing in phosphorus deficient soil might also have trouble reaching maturity. If you aren’t seeing many flowers, seeds, or fruits, get your soil tested!

Growfully Protip

Because phosphorus soil deficiency is hard to pick up on through plant signs, it’s a good idea to regularly test your soil. We recommend once every two to three years, plus whenever you are starting a new garden or you are having growth issues.

Soil testing for phosphorus deficiencies

We dive into soil testing a lot more in our soil health primer, but any good quality lab soil test will give you all the info you need to do proper phosphorous management. While there are at-home test kits, we’ve found them to be pretty unreliable for anything except testing pH.

Growfully Protip

Our favorite lab for soil testing is Waters Agricultural Laboratories. You can also check with your local county extension office—most have accounts with soil testing laboratories and can provide supplies and discounts (plus advice on reading your results).

How does soil pH impact phosphorus availability?

Having the right amount of phosphorus in your soil in one thing—making sure it’s available for your plants to actually use is another. Phosphorous is very reactive to other chemicals in the soil depending on the acid level of your soil—these chemical reactions “bind up” the phosphorous so it isn’t available for plant uptake. In alkaline soils (typically above the 7.3 pH mark), phosphorous binds with calcium. In acidic soils (below 5.5 pH), phosphorus binds with aluminum.