Question: I’ve been growing an Eastern redbud in a large pot on our somewhat-shady deck. It is nearly six feet tall, and now it is dropping all its leaves, but has no pests. We water it regularly so the soil is usually slightly moist. What’s wrong? How can we fix the situation?

Answer: The Eastern redbud is a favorite of this Garden Doctor. I just love the stunning blossoms in early spring. From your description, without actually seeing the plant, it is difficult to pinpoint an exact cause of the dropping leaves. Redbuds should do well in part shade as they tend to be an understory tree in the wild. They do prefer moist soil but can tolerate dry spells and do thrive in a variety of soils.

However, there is one clue that leads the Doctor to believe growing in a pot may not be the best choice but rather that an in-ground location may be better. Redbuds are generally not grown as container trees. They are very particular and do not like “wet feet.”

The tree may not have had this problem until now because the pot was large enough to keep the roots from sitting in water. But now the tree is larger and the roots, possibly, are sitting in too much moisture.

It is hard to say if the tree can be saved but cutting back on watering (wait until the soil is dry) or transplanting it to the ground might help.

Question: Something is eating my tomato plants, and I’m almost afraid to find out what it is. I’ve had tomato hornworms in other gardens, but this is the first time for my Davis garden. How do I determine what the problem is? What can I do about it?

Answer: Tomato hornworms, along with aphids, are the most common tomato pests. They are so named because of the horn or the thorn at the rear end. Correct diagnosis is the key factor and, since you have dealt with hornworms before, you no doubt had identified the problem with evidence of chewing and holes in the leaves. We associate these hornworms with tomatoes, but they are also found in and very fond of eggplants, peppers and potatoes.

Belonging to the Manduca species, they are probably the largest of the caterpillars you’ll find in your vegetable garden. Colored green with white stripes, these hornworms are difficult to detect, especially considering their size (up to 4 inches long — think the length of your index finger).

They will devour entire leaves and young stems as well as chew into the fruit.

Look for round smooth pale green eggs, laid singly on the leaves. If you see any of these, pick them off and dispose of them. Looking for the worms takes some patience because they blend in so well. They like to hang in the shade of the foliage, so look underneath leaves on the stems. Black droppings (frass) on the ground and on leaves closest to the ground indicate their presence.

Hand-picking them as you would with snails is very effective. Because of their size, you can also snip them in half with your shears. Bacillus thuringiensis (BT) can be very effective on smaller larvae.

The hornworm is a caterpillar and represents the larval stage of the hawk or sphinx moth. The moths overwinter in the soil as the pupae, so rototilling will destroy the pupae. If the pupae aren’t destroyed, they will emerge in late spring and begin the cycle of laying their eggs, which hatch in four to five days as a hornworm. The plants provide a good food supply and in four weeks the caterpillars are full size. At this stage of the cycle, the caterpillar makes its way into the soil to pupate.

Should you find a hornworm with white egg sacs covering its back, leave it. These are the egg sacs of the parasitic Braconid wasp and a beneficial predator that will defend your garden from this hornworm, and many other garden pests.

Confidential to Would-be Gardener: Don’t be fooled by the mild summer we’ve been having. It really is time to think about your fall vegetable crops! For many plants, it is the day length, more than the air temperature, that affects growth and maturation.

Find a spot among those still-green tomatoes to plant some lettuce seeds, and later some transplants of broccoli and cabbage. For more information about planting dates, go to http://ceyolo.ucdavis.edu/files/53274.pdf

— Send questions, addressed to the “Garden Doctor,” by email to [email protected], voice mail to (530) 666-8737 or regular mail to UCCE Master Gardeners, 70 Cottonwood, Woodland, CA 95695. Be sure to include your contact information, because any questions not answered in the Garden Doctor column will be answered with a phone call or email to you.

You can request the Yolo Gardener newsletter delivered by email and learn more about the Master Gardener program in Yolo County at http://ceyolo.ucdavis.edu/Gardening_and_Master_Gardening

Tomato HornwormW

Tomato hornworms are a common garden pest, gobbling up not only tomatoes, but eggplants, peppers and potatoes. Courtesy photo

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