What’s causing tomato and bean leaves to turn yellow?

QI have been a home gardener since 1976. This year, almost all of my 13 tomato plants have yellow leaves. It does not seem to matter whether the plant came from seeds, was bought or was a volunteer that came up on its own. They are all turning yellow.

The green beans — planted from seeds — are, too. I bought a load of compost from an Oakland company. Could the compost be the problem? Please help.

AAs an experienced gardener, you’re probably well aware of the multitude of diseases that can inflict our tomato plants, but there are two things about your garden this year that points to the likely problem.

Because all of the tomato plants — not just one or two — as well as your green beans, are suffering from the problem, I’d say the cause is a lack of nitrogen, which means, yes, the compost is probably the root of the trouble, excuse the pun.

If you relied on the compost to give your vegetables an infusion of nitrogen, then the compost might have been lacking in that area. If you still have the compost, you can check it with a simple soil test you can pick up at any nursery or home supply store.

It also could be that the plants have depleted the nitrogen in the bed — summer vegetables are heavy nitrogen users — and are in need of an infusion.

Look for a fertilizer formulated for tomatoes and other summer vegetables. Worm castings also are an excellent source of nitrogen. After the season is over, consider growing some cover crops — fava, crimson clover — to add nitrogen back into the bed.

QWe have been using recycled water from the Central Contra Costa Sanitary District to keep our shade trees and shrubs alive during this dry summer. Do you know if we can safely use the same water to water our fruit trees, such as apple, nectarine, plums and others?

I understand that the recycled water contains more salt than the regular water. Would we damage those trees by using recycled water?

Another question is about lantana. In one of your columns, you said overgrown lantana can be severely pruned back to a more compact form. Can the pruning be done at any time, even now?

AThere are two general concerns when it comes to using recycled water — possible pathogens in the water and salt stress. However, most experts agree that it can safely be used on garden plots and fruit trees.

When using it on edible plants and trees, be careful not to spray the fruit. Some experts say the water should only be used on vegetables that will be peeled or cooked, to prevent spreading pathogens. Others say you just need to wash the fruit really well.

The fruit on your trees isn’t likely to come in contact with the water, so there are no health concerns there, but the water can contain higher amounts of salt or salinity. It’s a problem people who irrigate with well water also may have.

While many fruit trees don’t have a super high tolerance for salt, they have some, and recycled water is considered safe to use.

To avoid issues, be sure to water deeply, which will help disperse the salt, and watch for signs of salt stress. The first you’re likely to see are leaves that look burned or wilted, despite the soil being wet. You can reduce levels of accumulated salt by occasionally irrigating with regular water, making sure to thoroughly soak the area.

As for the lantana, you can prune in the early spring or late winter, but never in the autumn. Lantana should be cut back 6 inches to a foot from the ground, or by two-thirds.