What Phosphorus is Right For Your Bulbs?

By on September 27, 2012

Find out why Tricia is smiling at a box of Seabird Guano! Hint: it has to do with the numbers on the front.

Why do we plant bulbs? So they’ll bloom! What makes bulbs bloom? Phosphorus.

Phosphorus is the P in the N-P-K numbers on fertilizers.

Phosphorus is a little bit sneaky though—and we’ll teach you the tricks to get the phosphorus to your bulbs.

Phosphorus stays put

We all add nitrogen fertilizers to the surface of our soil, and nitrogen moves through the soil, reaching the roots. Phosphorus doesn’t move, so add it near the roots at planting time. Mix in a powdered phosphorus soil amendment or fertilizer at the bottom of your planting hole.

Which source of phosphorus should you add? Keep reading.

Acid or alkaline soil

Test the pH of the soil where you’ll be planting bulbs. The pH ranges from 1 (most acid) to 7 (neutral) to 14 (most alkaline). It is likely that your soil is in the 5 to 8.5 range.

Here comes the chemistry: the pH of your soil affects how chemicals react. Bone meal is a good source of phosphorus, as is soft rock phosphate, but the nutrient can only be accessed in acid soil. In the photo above, Tricia is adding bone meal to her slightly acid Sierra foothills soil.

If you have alkaline soil, use Hi P Seabird Guano, or Hi P Bat Guano for phosphorus. That’s why Tricia is smiling at the Seabird Guano box—there’s a high phosphorus number on the front, and it’s phosphorus that will work in alkaline soil.

Tips for bulb planting

See all of Tricia’s tips on how to plant bulbs in our video.

Plant bulbs in the fall (with the right kind of phosphorus) and guarantee yourself a flower-filled spring!

  Comments (6)


Our local organic supply store sells PhosCal as a phosphorous fertilizer.  How does it compare with bonemeal?  Also, is there a bonemeal fertilizer that does not pose a heavy metal problem?

Posted by Sharon Elston on Sep. 29, 2012 at 8:42:20 AM


What is the difference between Mexican bat guano and other bat guano.  The p is dramatically different.  Our grove manager says to use the Mexican or one with low p for our fruit trees.

Posted by Lynn on Mar. 09, 2013 at 7:05:26 AM

Sharon, We don’t carry PhosCal so I don’t know what the numbers are. One of our bonemeals is a liquid, for instance, and it is 0-12-0 http://www.groworganic.com/liquid-bone-meal-qt.html I’m sorry, but I don’t have any information about heavy metal and bonemeal.

Posted by GrowOrganic.com on Mar. 09, 2013 at 1:55:38 PM


The guanos vary depending on the creature producing them and their diets. http://tinyurl.com/ahwcdns Mexican bat guano is low P. Click the link and you will see that bats in other countries can be high P.

Posted by GrowOrganic.com on Mar. 09, 2013 at 2:03:58 PM


Your article says that phosphorus doesn’t move.  How do you get this to the bulbs after the initial planting, particularly when you have a naturalized area where you couldn’t dig it into the soil?  Thanks

Posted by Amy on Apr. 07, 2013 at 8:38:04 AM

Amy, You can only add the phosphorus at root level at planting time. Works whether you are planting in beds or naturalizing. You can top dress when leaf tips and then flowers emerge with a high phosphorus fertilizer like this http://www.groworganic.com/rose-flower-and-bulb-mix-4-8-4-6-lb-box.html

Posted by GrowOrganic.com on Apr. 08, 2013 at 11:48:46 AM

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