philodendron red congo

Cause

Yellow leaves on a Philodendron 'Red Congo' (a self-heading cultivar of P. erubescens) most often trace to environmental stress rather than disease. Jack Kramer's 1974 monograph lists heat too high, humidity too low, not enough fresh air, and soil too dry or wet as the four probable causes, and notes that yellow and wilted bottom leaves are a telltale sign of over- or underwatering because both practices damage the root system and leave the foliage dehydrated.

Solutions

• Remove the plant from its pot and inspect the roots: gently rap the pot to loosen the rootball and look for mushy black roots (overwatering) versus a dry compacted mass with no fine white roots (underwatering), since both produce the same yellow-leaf symptom in philodendrons.
• Correct the watering rhythm: for pots up to twelve inches water twice a week in spring, summer, and fall, and once a week in winter; water larger specimens once a week except in winter, when every two weeks is enough.
• Stabilize the environment: move the plant away from hot radiators or cold drafts, raise humidity around the foliage, and use room-temperature water rather than cold tap water, since cold water alone can ring yellow halos on philodendron leaves.

Cause

Root rot in Philodendron 'Red Congo' is overwhelmingly a drainage problem. Jack Kramer's 1974 philodendron monograph flags collapse of the plant from root rot caused by poor drainage as a primary failure mode, and warns that waterlogged soil will ruin philodendrons; the cultivar's dense, self-heading rosette of large leaves makes an already slow-drying rootball even more prone to saturation in a glazed or non-draining container.

Solutions

• Repot into a container with drainage: drill quarter-inch drainage holes in the bottom of the pot if it has none, since most glazed pots do not have drainage holes and waterlogged soil can ruin philodendrons.
• Use a porous, chunky aroid mix and repot every year for plants under sixteen inches, or every second or third year for larger specimens, because plants have drained nutrients from the soil and a compacted mix holds too much water against the roots.
• After repotting, water only when the top of the mix is dry, empty any standing water from the saucer, and keep the plant in good light so it actually uses the moisture you give it rather than sitting in a dark, wet rootball.

Cause

Spider mites on Philodendron 'Red Congo' are the same microscopic red arachnids that attack the wider genus: Jack Kramer's 1974 chart describes fine webs at leaf and stem axils with leaves mottled, turning gray or brown and crumbly, and he notes that dry crumbling leaves, brown leaves, and identical spider-mite damage can all show up on philodendrons kept where the air is hot and dry.

Solutions

• Blast the plant with a vigorous water spray from above and underneath to physically break the webs and dislodge the mites, repeating every few days while the infestation is active.
• Wipe foliage weekly with a damp cloth or mist with clear tepid water; this cleansing tends to remove insect eggs and spider mites and discourages other pests, and is preferable to leaf-shining preparations that clog leaf pores.
• If the infestation is heavy, apply a miticide such as Dimite or Aramite, or rotate to insecticidal soap and horticultural oil, treating both leaf surfaces and the leaf-stem axils where the mites and their webs concentrate.