Are Yellow Leaves on Tomato Plants Due to Too Much or Too Little Water?
- Poorly drained soil may be the result of composition or construction. Clay soil, compacted soil and areas of standing water are considered poorly drained. These soils keep roots wet, leading to root rot. It is easy to overwater plants on such a soil. Sandy soils pose the opposite problem, as they often drain too freely. Plants growing on sandy soils require more frequent watering, as the soil doesn't hold moisture well. Their tendency to drain water leads to a loss of nutrients, which causes yellow leaves.
- Overwatering can lead to a loss of nutrients from the soil, washing away those already in the soil and those offered through applications of fertilizer. When nutrients are lacking, tomato leaves may yellow. A deficiency of nitrogen often shows within older leaves first. Sulfur and zinc deficiencies affect younger leaves before older leaves. Magnesium deficiency affects younger leaves in severe cases, older leaves develop yellow coloring between their veins and tomato plants may drop their older leaves. Copper, iron, zinc and manganese deficiencies lead to yellowing between the veins of tomato plant leaves, and copper deficiency causes the death of young leaves. The University of Minnesota Extension recommends growers use soil testing along with plant analysis to better identify what nutrients are lacking, as some soil tests alone do not provide reliable information regarding fertilizer needs.
- Water indirectly causes leaves to yellow because of fungal infection. Several fungal diseases include yellow leaves as a symptom. These infections develop due to damp conditions that occur because of rain, overwatering or watering at the wrong time of day. Crowding of plants also leads to disease, as the foliage does not get enough air circulation to help dry the leaves. Fungal diseases usually have additional symptoms allowing you to identify their presence as a cause of yellowing leaves. Some symptoms of Fusarium wilt cause plants to develop the same appearance as when they've been over- or underwatered. These symptoms include yellow leaves, drooping leaves and a wilted appearance.
- Improve poorly drained soils by correcting aspects causing poor drainage. Amend clay and sandy soils with organic matter. This increases the soil's aeration and ability to retain nutrients. Tomatoes require the equivalent of 1 inch of rain per week. Gardeners should water their plants consistently at ground level and do so in the early morning allowing the plant's foliage to dry quickly. These steps help prevent fungal infections.
