Yellow is not mellow when it should be green. Why are the leaves of my cleome yellowing? When plant leaves fade to gold, the first culprit is lack of sun. The other causes are not as obvious.1. Mulch: Well intentioned gardeners who mulch heavily with shredded hardwood may notice discoloration of the leaves of annual flowering plants. During spring rains tannins from the wood leach into the top surface of the soil and are absorbed by the roots of young plants, especially annuals. The result may be yellowed leaves, especially at the base of the plant.
2. Too much sun: New plants, especially those grown in a greenhouse may discolor in the full sun. It's best to plant new growth during the rainy overcast days of spring or fall to minimize stress on the plant. If that's not possible, shield the plant with cardboard or a partially (but not fully) tipped dark plastic pot for a few days. The plant will eventually adjust to sunlight.3. Moisture stress. The most common cause of yellowing leaves is too much, or too little water. Plants all have different water requirements. First look up the actual needs of a specific plant. Most full sun plants require more water than shade lovers. Overwatering in the shade also leads to fungal infections. Best measurement is still by touch. Poke a finger into the surrounding soil. It should feel damp but not soaked. If the area is powdery, then water. If it is soupy, wait until it drains.
4. Inadequate drainage: Heavy clay soils cause water to pool. The top of the plant's root ball may appear to be adequately watered, but clay substrate causes water to accumulate below the surface, at the roots. If the yellowing plants are in a pot, drill drainage holes, or tip the pot on its side onto the grass allowing stagnant water to drain.
5. Fertilizer burn: Well meaning gardeners often treat yellowed leaves with heavy doses of fertilizer. Unfortunately, no amount of fertilizer will help an ailing plant. The added introduction of plant stimulants only causes further plant stress. Even healthy plants (and grasses) will turn yellow if too much plant food is applied. It's better to introduce weaker, more frequent doses, if needed.
6. Chemical over-spray: Droplets from lawn or tree chemical spraying can attach to the leaves of annuals or perennials and cause burning of the leaves. Water the garden heavily after a visit by Lawn Green, directing the water spray at leaves-rather than roots.7. Nature: Some plants simply turn yellow earlier than others, and before the official start of fall color. Bleeding heart, for example, turns yellow in mid August. Hosta begins to age in early September.
There's no spray or plant pill for yellowing leaves. Remove those that have turned--they won't return to the green zone. If the base of the plant remains healthy, perennials will likely return the following year. If the issue is be cultural, relocate, shelter, adjust watering or fertilizer practices.
Yellowing leaves are unavoidable.
They're how plants communicate their displeasure with us. Related topics:
Why Are the Maple Leaves Brown?
Will My Garden Survive This Drought?