Dear Edward,

Thank you for reaching out to the UVM Extension Master Gardener Program with your question.

You did not include photos of the plants with your question so unclear if the yellowing is generalized or involves just the lower leaves of the plants. You do not mention the presence of spotting, wilting or browning of the leaves. There are a wide variety of issues that can cause yellowing of plant leaves. The fact that it is occurring in 2 different types of plants in the same area of the garden suggests environmental factors. We have experienced some extremes in temperatures over the past month with some very hot days followed by much colder temperatures. This type of environmental stress can contribute to yellowing of the leaves. We also had a dry stretch followed by a lot of rain. Too much or too little water can also contribute to yellowing of the leaves. You did not mention if you have tomato or basil plants in other parts of your garden that are doing well. Could there be poor drainage in that part of the garden? Is there more shading in that part of the garden? Lack of light can cause yellowing of the leaves. Nutritional deficiencies can contribute to yellowing of the leaves. Cold temperatures may impair the plant’s ability to take up nutrients. Did you add nitrogen before planting? Potassium or magnesium deficiency may also result in yellowing of the leaves. If your soil pH is not optimal, plants may not be able to access nutrients in the soil even if the soil nutrient levels are adequate.

You should look to see if the new growth on the plants appears greener in color. If the problem is related to the cold the problem should improve with increased soil temperature as the season progresses. You may consider side dressing the plants with some fertilizer if you have not already added amendments to the soil. If the situation does not improve it would be helpful to send photos of the plants with a follow up to your question.

The following resources may be helpful:

https://extension.umd.edu/resource/vegetable-seedlings-or-transplant-leaves-yellowing-turning-white-or-are-spotted-or-scorched/

https://extension.msstate.edu/sites/default/files/publications/publications/p2975_web.pdf