Dear Master Gardener: Can you tell me if mowing off my rhubarb will kill or hurt it. My lawn boys mowed off my rhubarb. What should I do?
Answer: As long as you still have some root in the ground it should come back next year. In the future, it is best to remove the stalks and leaves after the first killing frost.
Dear Master Gardener: Can I bring my herbs inside for the winter so I can continue to have fresh herbs for cooking?
Answer: Yes, but it can be challenging in the hot, dry conditions found in most homes in the winter. Herbs grown indoors will probably be less productive than when they are grown outdoors. Bring potted herbs inside before the first frost. Some herbs, such as chives, mint, and tarragon can tolerate a light frost. Keep herbs in a room that has daytime temperatures of at least 65-70 degrees and nighttime temperatures of 55-60 degrees. Most herbs need at least six hours of direct sunlight, so give them as much light as you can by placing them in a sunny, south-facing window or under cool white fluorescent lights for 14-16 hours. If you are growing potted herbs on a windowsill, rotate the pot for uniform growth. If herbs do not receive adequate light, they will become thin and spindly, produce smaller leaves, and have less aroma. You can increase humidity by setting the pots of plants on saucers with moist pebbles. Water only when the potting medium feels dry, but never allow the plant to wilt.
Dear Master Gardener: My husband is always in a hurry to cut back perennials and clean up the gardens. Is it too early to cut them back? Can they be cut back in spring instead?
Answer: Wait to cut back perennials until their foliage is damaged by frost and they are brown and dead. As long as the plant is green, it continues to build up carbohydrates through photosynthesis and store them in its roots for next year’s growth. Many perennials do not need to be cut back at all before winter and some provide beautiful winter interest and a source of food for birds. Ornamental grasses and perennial seed pods, such as those found on Baptisia, can add striking interest to a winter landscape. You can leave them standing until spring then cut them back before new growth appears. Many birds rely on the seed heads of dried perennials for food. If you would like to provide a food source for birds, leave Rudbeckia (black-eyed Susan), Echinacea purpurea (purple coneflower), and Heliopsis in place for the winter. As we experienced last winter, we can have some very frigid temperatures. Perennials that are hardy to zone 4 are more likely to survive our cold winters if you don’t cut them back, which allows leaves to collect around them and snow to insulate them.
It is important to cut back any plants with disease or insect problems to reduce the chance of infection next year. If you have problems with slugs around your hostas, cut them back as soon as they are frost-damaged and remove all their leaves from the ground, as the dead leaves can harbor slug eggs that will hatch next year. Cut back Peonies within two inches of the ground when they have been damaged by frost and are mostly brown. Heuchera (coral bells), Dianthus, Moss Phlox, Hellebores, and Tiarella should not be cut back.
Dear Master Gardener: Is there anything I should do to my garden tools before storing them away for the winter?
Answer: Garden tools will last longer and work better if you keep them clean and well-maintained. Ideally tools should be cleaned each time you use them, which will keep diseases from spreading in your garden. Because plant pathogens can survive on your tools and then spread in your garden, clean them with a 10% bleach solution or household disinfectant. Keep in mind that bleach can be corrosive to metal so you may want to keep a bottle of disinfectant (like Lysol) with your gardening tools and sanitize (especially pruning shears) each time you use them. Some gardeners squirt hand sanitizer on their pruning shears between plants. Shovels, rakes, trowels and other tools can be washed with water and then dried well. Another method of cleaning shovels and pitchforks is to slide them up and down in a bucket of sand (you can also add some motor oil to the sand). To prevent rust or minimize it, lightly oil your tools made of steel. Before putting them away for the winter you may want to sharpen your trowels, shovels, and hoes with a hand file and your pruning shears and garden knives with a honing stone. When spring arrives, you will be glad your tools are in tip top shape!
Dear Master Gardener: Can I divide my Karl Foerster feather reed grasses in the fall? Should I cut my grasses down now or wait until spring?
Answer: Calamagrostis × acutiflora “Karl Foerster” can successfully be divided in the fall, but most other grasses respond best to spring division. Cutting back grasses in the fall, especially younger plants, may result in winter injury and the beauty of the plants in the winter landscape is lost. In late winter or early spring, before new growth starts, cut back grasses to the ground to remove the previous year’s growth. If the plants are not cut back, spring growth can be delayed and large plants will look unattractive throughout the year. “Karl Foerster” begins to grow very early in spring and can be cut back in March or early April.
You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, emailing me at umnmastergardener@gmail.com and I will answer you in the column if space allows.
University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.