By Ken Lain, the mountain gardener
The advice that follows is good for houseplants as well as outdoor container and landscape plants. It is an outline of the most common local plant problems. Many plant problems have similar symptoms and sometimes plants exhibit combinations of problems and their symptoms. The explanations below are well thought through and should prove helpful the next time garden plants look sick. Print this list and add it to your garden journal or bookmark it for later reference.
When diagnosing a sick garden plant, first eliminate the obvious by checking for signs of insects or disease. Nutrient-deficient plants often manifest as foliage discoloration or distortion. Foliage discoloration and stunted plants can be caused easily by soil that is too wet and drains poorly, or soil that is too compacted for good root growth. Extreme cold or heat will slow plant growth and affect flowering and fruit set. For definitive diagnoses, consult the plant experts here at Watters Garden Center.
Plants do require a mix of nutrients to remain healthy. Nutrients needed in relatively large amounts are called the macronutrients, which include: nitrogen, potassium, phosphorus, calcium, sulfur, and magnesium.
The handful of additional nutrients that are required for plant growth, but in much smaller amounts, are called micronutrients; they include boron, copper, iron, manganese, molybdenum, and zinc.
Plants assimilate all of these nutrients through their roots. As water transfers the nutrients from the soil to the plant roots, an essential requirement of a plant’s absorption of nutrition is sufficient water.
A second requirement is the appropriate soil pH for the plant being grown. Each plant prefers a specific pH range to be able to access the nutrients in the soil. Some plants are fussier than others, but if the soil pH is too acidic or too alkaline most plants will not be able to take in nutrients no matter how rich the soil. It’s good to check your soil pH once each growing season.
Symptoms and Treatments of Nutrient-Deficient Plants
- Calcium (Ca)
- Symptoms: New leaves are distorted or hook-shaped. The growing tip may die. Contributes to blossom end rot in tomatoes, tip burn of cabbage, and brown/black heart of escarole & celery.
- Sources for calcium: Any compound containing the word ‘calcium’. Also gypsum.
- Notes: Not often a problem of deficiency, as too much will inhibit other nutrients.
- Symptoms: Older leaves, generally at the bottom of the plant, will yellow. Remaining foliage is often light green. Stems may also yellow and may become spindly. Growth slows.
- Sources for nitrogen: Any compound containing the words: ‘nitrate’, ‘ammonium’, or ‘urea’. Also manure.
- Notes: Many forms of nitrogen are water-soluble and wash away quickly. Use an organic or slow-release form of nitrogen like Watters ‘All Purpose Plant Food’.
- Symptoms: Slow growth and leaves turn pale yellow, sometimes just on the outer edges. New growth may be yellow with dark spots.
- Sources for Magnesium: Compounds containing the word ‘magnesium’, such as Epsom salt.
- Symptoms: Small leaves that may take on a reddish-purple tint. Leaf tips can look burnt and older leaves become almost black. Reduced fruit or seed production.
- Sources for Phosphorus: Compounds containing the words ‘phosphate’ or ‘bone’. Also greensand.
- Notes: Very dependent on soil pH range.
- Symptoms: Older leaves may look scorched around the edges and/or wilted. Interveinal chlorosis (yellowing between the leaf veins) develops.
- Sources for Potassium: Compounds containing the words ‘potassium’ or ‘potash’.
- Symptoms: New growth turns pale yellow, older growth stays green. Stunts growth.
- Sources for Sulfur: Compounds containing the word ‘sulfate’.
- Notes: More prevalent in dry spring soils.
- Boron (B)
- Symptoms: Poor stem and root growth. Terminal (at end of branch) buds may die. Witches’- brooms sometimes form.
- Sources for Boron: Compounds containing the words ‘borax’ or ‘borate’.
- Symptoms: Stunted growth. Leaves can become limp, curl, or drop. Seed stalks also become limp and bend over.
- Sources for Copper: Compounds containing the words ‘copper’, ‘cupric’ or ‘cuprous’.
- Symptoms: Growth slows. Younger leaves turn pale yellow, change often starting between veins. May develop dark or dead spots. Leaves, shoots, and fruit diminished in size. Failure to bloom.
- Sources for Manganese: Compounds containing the words ‘manganese’ or ‘manganous’
- Symptoms: Older leaves yellow, remaining foliage turns light green. Leaves can become narrow and distorted.
- Sources for Molybdenum: Compounds containing the words ‘molybdate’ or ‘molybdic’.
- Notes: Sometimes confused with nitrogen deficiency.
- Symptoms: Yellowing between veins of new growth. Terminal leaves may form a rosette.
- Sources for zinc: Compounds containing the word ‘zinc’.
- Notes: Can become limited in higher soil pH.
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Important in October – The most important plant feeding of the year is in the month of October. Feed everything in the yard by the end of the month. I created easy to apply Watters ‘All Purpose Plant Food’ 7-4-4, a unique blend of nutrients that local plants love. Pay special attention to evergreens like pine, fir, spruce, cedar, and cypress, especially those native pines on your property.
Until next week, I’ll see you at Watters Garden Center.