Q: I’ve never quite figured out when it’s appropriate to harvest garlic. Do you have any idea? D.L., Swanville

A: A general rule of thumb to use: Harvest when leaves have started to die back and only five or six green leaves remain. Garlic should be harvested before the cloves have separated within the bulb. Cure the harvested garlic in a dry, shaded area that has adequate air circulation and an ambient temperature between 60 and 70 degrees F.

Q: The leaves of my bee balm plants have all turned brown with a silvery white powder coating. Do you know if this is a disease I should be concerned about? P.M., Brooksville

A: You’ve described a common plant disease often spotted in late summer. Powdery mildew is particularly destructive to the leaves of our favorite landscape plants, including bee balm, phlox, rose, euonymus and lilac. The disease usually isn’t fatal, but it very much compromises the appearance of garden plants.

More than one fungal species causes the symptoms of the disease we call “powdery mildew.” The fungi usually cause grayish or white powdery growth on the leaves or succulent tissues (such as the flowers and fruits) of plants. Infected leaves often drop off stems prematurely, weakening the host plant and perpetuating the life cycle of the disease. Sometimes developing leaves and shoots become distorted, stunted or dwarfed by mildew fungi, causing a “witches’ broom” effect.

Prevention of powdery mildew is probably the best defense against the disease. Plant resistant species in sunny locations. Prune or thin plants so that adequate air circulation between plants is possible. Prune out affected tissue if the infection is localized.

Q: I dread the thought of giving up my hearty crop of tomatoes once fall hits. Is there something I can do to protect them from the frost? I’ve heard about protecting other plants from frost with row covers, but I’m not sure that will work for plants. Any idea? H.M., Belmont

A: Tomato plants can be protected from the frost with plastic or row covers if a light frost is predicted in autumn. Gardeners have even reportedly used blankets or sheets.

Green tomatoes can be harvested and set out to ripen, so don’t dispose of the green tomatoes until you’ve attempted to encourage them to ripen off the vine!

Q: I’ve saved some seeds from plants in my garden. Some of the different types of seed have a lot of debris in them. Is it OK to store the seeds with that debris in there or should you really take pains to clean it all out? M.D., Milbridge

A: It really is advisable to clean the chaff from the seed. Winnowing the seed by pouring it through a stream of air – either by a fan set on a low speed or simply by blowing gently – is suggested to eliminate the excess chaff. Reducing chaff in stored seeds may reduce moisture, thereby reducing the chance of damaging or ruining seeds through untimely absorption. Elimination of chaff may also reduce the number of inoculants – fungi, bacteria and viruses, for example – that could lead to infection of seeds and young plants.