KNOWitall
Ask the Expert By Debra Ricigliano
Whether to Reuse or Replace Container Garden Soil Every Year Q: This past summer, I did most of my gardening in containers. I grew my vegetables, herbs, and most of my flowers this way. I was very successful and plan on doing this again. Will I have to purchase new potting mixture to fill my containers or can I reuse the soil? A: Yes, you can reuse your potting mixture, providing your plants were healthy and did not have root diseases. Reusing it is a money saver, is a form of recycling, and reduces demand for peat moss (the mining of it releases large amounts of CO2). It is best to empty the media, after removing the plant debris, into a trash can or heavy-duty trash bags for the winter. This allows you to clean the containers and protects the growing media from the elements. Before using it next season, mix it 50:50 with fresh potting mixture and/or compost.
Winter Watering of Newly Planted Shrubs and Trees
Q: Back in October, we had our front landscape beds redone. There is a mixture of shrubs and a redbud tree. My question is about watering these young plants. It seems that we have not had much rain lately. I am hesitant to stop watering them but was wondering when I can stop. A: Good for you that you are taking the proper measures to care for your new landscape. Instead of watering on a schedule, check the soil moisture around the plants about once a week. This reduces the chance of overwatering. Probe down about 5 inches below the mulch around the base of the plants, using your finger or a stick to see if the soil is moist. If so, do not water. If it is dry, you should irrigate, directing the water to the root zone. The soil should dry out between waterings. Once the ground freezes, you can stop checking. Often, our soil remains moist as spring returns. Once the plants start growing and temperatures warm up, begin this watering process again. 22
WASHINGTON GARDENER
DECEMBER 2021
Spiny witch hazel gall aphids on the back of a birch leaf. Photo courtesy of UMD HGIC.
New landscapes should be watered for about two years after planting to reduce plant stress during the establishment period.
Switching Landscapes to Majority Native Plants
Q: My winter project is planning how I can convert my garden to native plants. However, I do have some non-native favorites like azaleas, osmanthus, nandinas, and big-leaf hydrangeas. Is it okay to have a mixture of native and non-native plants in a landscape? A: The interest in planting native plants grows every year and is a positive step for helping pollinators, beneficial insects, and wildlife; reducing the introduction of invasive plants into the environment; and so much more. It is recommended that at least 70% of a landscape be native plants. As long as a non-native garden favorite is not proven to be invasive, it can be part of a diverse landscape. The one shrub that should be removed and replaced on your list is nandina (Nandina domestica). It is on the radar of the Maryland Department of Agriculture as being invasive (see Tier
2 Invasive Plants: https://mda.maryland.gov/plants-pests/Pages/maryland_ invasive_plants_prevention_and_control. aspx). Nurseries and landscapers must inform buyers of that fact and that alternatives should be considered. Also, it has been documented that nandina berries may be toxic to birds. Virginia sweetspire (Itea virginica), fothergilla (Fothergilla gardenii), and spicebush (Lindera benzoin) are three native replacements to consider. o Debra Ricigliano is a Certified Professional Horticulturist, who has worked as a horticulture consultant for the University of Maryland Extension Home and Garden Information Center since 1997. She is a graduate of the Institute of Applied Agriculture at UMCP. To ask a gardening or pest question, go to http://extension. umd.edu/hgic and scroll to “connect with us.” Digital photos can be attached.
