Nutrient Basics - Phosphorus

Happy Independence Day!

Phosphorus (P) is also a vital nutrient for all plants that needs to be available to plants in all stages of growth. Phosphorus is the second number in fertilizers, so that a 5-15-5 fertilize would be 15% phosphorus. Specifically, phosphorus is crucial in root formation, flowering, fruiting and ripening. So, you should provide your plants with a fertilizer that has the middle number as the highest when you have seedlings, newly rooted cuttings, and from beginning to end during flowering/fruiting.

Signs of a Phosphorus Deficiency -- Early in the deficiency, plants look almost too healthy with what appears to be normal but undersized plants with dark green leaves. However, you may notice the leaves and or their veins and leaf stems (called petioles) frequently changing to purple, especially the undersides of leaves. Leaves may curl under with some plants. Sometimes the leaves will turn a gray brown with a phosphorus deficiency and you may mistake this for a fungal infestation. Look for the color change to be at the leaf tips with a phosphorus deficiency where as a fungal infestation will be all over the leaf in a more random pattern. Fungi can develop when water is allowed to remain on the leaves if you mist your plants or they are growing outdoors. Cold water can also be a cause of spotting. Use room temperature water when watering and misting. You will notice very poor flowering and fruiting if you have a phosphorus deficiency.

Phosphorus Deficiency – can occur in cold, wet or very acidic (below pH5) soils; also very alkaline soils (above pH 7.3). You will need to adjust the pH if it is below 5 or above 7.3 since no matter how much fertilizer you add it won’t be available to plants at those extreme pH’s. You should also consider potting up your plants with a pH problem the new soil will be a quick fix but you should still adjust the pH so the problem does not come back.

Bone meal is a good organic source of phosphorus and you can add this to a soil mix.

Good Growing
Dr. E.R. Myers

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