Plant Problem Diagnosis Key / Nutrient problems
Nutrient
Phosphorus deficiency
P
Phosphorus moves out of old leaves to new ones. Plants grow slowly and older leaves turn dark and purplish. Cold soil limits uptake even when the soil has plenty.
Signs
- Dark, dull green leaves with purple or reddish tints, older leaves first.
- Purple stems and petioles; slow growth.
- Common in cold spring soil; often fades as the soil warms.
What favors it
Cold spring soil and very low soil phosphorus.
Prevention
- Test the soil before adding phosphorus.
- Keep soil pH near 6-7.
Often confused with
Growing conditionsCold and frost injury
DiseaseTomato spotted wilt and impatiens necrotic spot viruses
NutrientNitrogen deficiency
Sources
- Nutrient Deficiency of Vegetable PlantsUniversity of Maryland Extension
- 4 key nutrient deficiencies to scout for early in the seasonUniversity of Minnesota Extension
Treatment by crop
Cultural, biological and chemical options in the order to use them, and notes written for each crop.
Identification is free. Treatment is on the Home and Pro plans.
Questions in the key that lead here
- Look the plant over, leaf undersides included. Are insects, mites, slugs, eggs, webbing or droppings on it?
No, only damage or discoloration - Where is the problem?
Leaves - What does the leaf damage look like?
Color change without distinct spots - Where did the color change start?
Older, lower leaves - What do the older leaves look like?
Dark green to purple or reddish, dull
Not a match? Start the key or describe what you see.
More from university Extension: search Extension pages on phosphorus deficiency, or find a plant diagnostic lab through your state's Extension.