Richard Nunnally’s gardening column

Q:Could you suggest something I can use as mulch for my vegetable garden that would allow me to consider my produce organic? What about layers of newspaper with rotted sawdust on top?

Answer: You can use newspaper and sawdust. However, you have to be careful with the sawdust to make sure it has aged. Fresh sawdust contains a large amount of fresh resins and the pH can be very acidic. Clean straw is often used as mulch by many organic gardeners. The straw can then be removed at the end of the season. Q:Some of my iris have root rot and they smell rotten. What can I do? Also, is this something that the daylilies could catch? If so, how could I treat them?

Answer: Your iris may have been attacked by the iris borer. That causes decay in the tuber. The best way to deal with it now is to dig them up, dispose of any infected tubers and divide the remaining healthy ones. Treat the healthy tubers with Sevin when you plant them. Next spring you'll need to treat them again, when the new leaves are about 5-6 inches tall. You may have to treat each spring for a couple of years to get complete control. Iris borer is not a threat to your daylilies, so you won't need to treat them.

Q:What do you think of putting salt on weeds?

Answer: Salt will kill weeds. The only problem is that it is not selective. Meaning, if it gets on good plants it will kill them, too. If it is applied too heavily and washes onto the soil, it can soak into the ground and kill other plants through the roots. Some organic gardeners use rock salt to control weeds and grasses in asparagus beds. It seems that asparagus is much more tolerant of salt than most other vegetables.

However, I found several conflicting articles from various extension services, some recommending it and some not. All of them warned about the potential for runoff onto desirable plants and the potential for buildup in the soil over time, which could have an adverse effect on the young spears. Yes, salt will kill weeds, but I'm not sure it's worth the risk. Q:I have a fairly young witch hazel that has gotten these conical galls on the leaves for the past two summers. Someone told me that they are called "witches hats." Last year I pulled off all of the infected leaves and then forgot about it until they reappeared recently. Should I have sprayed or can I do it now? Can you tell me what is going on and give me any suggestions as to what to do about it?

Answer: The growth you're seeing called "witches hat" is a black gall, made by a certain species of hornet. Similar galls can also be made by wasps, or aphids. The insect stings the leaf, causing a gall that is in the shape of a witches hat on the leaf. The gall provides a place for the insect to make a nest. It doesn't hurt the tree and by the time you see it, the damage is already done. I call this a cosmetic problem, because it can affect the appearance of the leaves, but it's certainly not worth spraying the tree to prevent it.

Q:Can you tell me what causes tomato wilt? The plants seem perfectly healthy and all of a sudden they start to wilt and die.

Answer: There are two fungi that cause fusarium wilt and verticillium wilt on tomatoes.

According to a publication from the Ohio State Extension Service, the wilt organisms usually enter the plant through young roots and then grow into and up the water-conducting vessels of the roots and stem. As the vessels get stopped up and collapse, the water supply to the leaves is blocked. With a limited water supply, leaves begin to wilt on sunny days and recover at night. Wilting may first appear in the top of the plant or in the lower leaves. The process may continue until the entire plant is wilted, stunted or dead. Tomato and potato plants may recover somewhat but are usually weak, unthrifty, and usually produce low-quality fruit.

There is no control once the plants have become infected and are showing signs of wilt. When you buy your plants or seeds, be sure to ask for wilt-resistant varieties. However, even resistant varieties can get the wilt if the plants are planted in the same place every year.

Richard Nunnally is a freelance writer and host of WCVE's monthly gardening show, "Virginia Home Grown." He can be contacted at .