Overwintering Tender Garden Plants - Ep. 323

Every fall I look at my pepper plants loaded with fruit and my rosemary at its biggest, and I hate the idea of handing them over to the first hard freeze. The good news is you don't have to. Peppers, rosemary, and geraniums are all perennials somewhere in the world, and basil will keep going for a while on a windowsill if you start it right. But whether a plant makes it to spring gets decided mostly before it ever comes through the door.

In this episode we're talking about which plants are worth the space, when to bring them in, and whether to keep them growing, put them to sleep, or just take cuttings. Then we'll get into my step-by-step for leaving aphids, spider mites, whiteflies, and fungus gnats outside, including why dish soap isn't the same as insecticidal soap and how long to keep new arrivals away from your houseplants. We'll finish with plant-by-plant care for peppers, rosemary, basil, and geraniums, plus a place where the experts don't agree.

Let’s dig in.

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References and Resources:

Pests and Insecticidal Soap

• Iowa State University Extension and Outreach, Yard and Garden — Can I Use Dish Soap Instead of Insecticidal Soap to Treat for Insect Pests? (detergent vs. true soap, phytotoxicity, contact-only action, reapplying): https://yardandgarden.extension.iastate.edu/faq/can-i-use-dish-soap-instead-insecticidal-soap-treat-insect-pests
• University of Florida IFAS Gardening Solutions — Soaps, Detergents and Pest Management (don't treat drought-stressed plants or above 90°F): https://gardeningsolutions.ifas.ufl.edu/care/pests-and-diseases/pests/soaps-detergents-and-pest-management/
• Nebraska Extension in Lancaster County — Washing Pests Away, Sarah Browning (2–3 applications at 4–7 day intervals, testing a small area first): https://lancaster.unl.edu/washing-pests-away/
• University of Minnesota Extension — Houseplant Pests (spider mite white paper tap test, mealybugs, fungus gnat management): https://extension.umn.edu/news/houseplant-pests
• Iowa State University Extension and Outreach, Yard and Garden — Spider Mites on Houseplants (dry winter air, stippling, webbing, rinsing in the shower): https://yardandgarden.extension.iastate.edu/article/2007/12-5/SpiderMites.html
• Iowa State University Extension and Outreach, Yard and Garden — Fungus Gnats in Houseplants (overwatering, letting soil dry): https://yardandgarden.extension.iastate.edu/article/2023/02/fungus-gnats-houseplants

• New Mexico State University, Southwest Yard & Garden — Chiles Can Be Grown Year-Round if They Are Brought Indoors (south window with about 4 hours of sun, nights around 50°F, underwatering losses, monthly fertilizer): https://swyg.nmsu.edu/2014/101814.html
• New Mexico State University, Southwest Yard & Garden — Chiles for New Mexico Holiday Houseplants (chiles as frost-tender perennials): https://swyg.nmsu.edu/2007/110307.html
• Ask Extension — Overwintering Peppers (nights above 50°F, days around 70°F, artificial light for fruiting; hot peppers more resilient; dormancy option): https://ask.extension.org/kb/faq.php?id=855650

• University of Illinois Extension, The Garden Scoop — Rosemary, Ryan Pankau (50–60°F indoors, very bright light, hardiness zone 7, 'Arp' and 'Hill Hardy' to zone 6, outdoor protection): https://extension.illinois.edu/blogs/garden-scoop/2018-10-18-rosemary
• Nebraska Extension in Lancaster County — Rosemary, An Herb for All Seasons, Sarah Browning (zones 7–10, 50–55°F indoors, watering): https://lancaster.unl.edu/rosemary-herb-all-seasons
• University of Arkansas Cooperative Extension — Rosemary, Janet B. Carson (overwatering as the biggest indoor risk, coolest sunny room, holiday topiaries): https://www.uaex.uada.edu/yard-garden/home-landscape/adgrosemaryjan2018.pdf
• University of Wisconsin Plant Disease Diagnostics Clinic — November 2020: Houseplant Horrors (powdery mildew on rosemary indoors, kitchen humidity): https://pddc.wisc.edu/2020/11/11/november-2020-houseplant-horrors/

• Brindisi, L.J., & Simon, J.E. (2023). Preharvest and postharvest techniques that optimize the shelf life of fresh basil (Ocimum basilicum): a review. Frontiers in Plant Science 14: 1237577 (chilling injury below about 54°F and severe below 50°F): https://doi.org/10.3389/fpls.2023.1237577
• University of Illinois Extension, Flowers, Fruits, and Frass — Growing Basil in Your Backyard, Brittnay Haag (tender annual, flowering makes plants woody and bitter, digging before frost extends the season): https://extension.illinois.edu/blogs/flowers-fruits-and-frass/2020-05-13-growing-basil-your-backyard
• Cornell Cooperative Extension Tompkins County — Herbs for Your Winter Windowsill, Pat Curran (digging basil in late summer, cutting back by a third to a half, rosemary leaves don't wilt, 1-gallon pots, separating outdoor plants from houseplants): https://bpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/c/10116/files/Windowsill-Herbs-Pat-Curran-March-2017-21jwe6n.pdf
• University of Illinois Extension — Keep Growing Herbs Indoors This Fall, Winter, Christopher Enroth (6–8 hours of bright light, 12–16 hours under lights, 70°F or below): https://extension.illinois.edu/news-releases/keep-growing-herbs-indoors-fall-winter
• Iowa State University Extension and Outreach, Yard and Garden — Can I Grow Herbs Indoors Over the Winter? (rosemary may need grow lights, clay pots, watering): https://yardandgarden.extension.iastate.edu/faq/can-i-grow-herbs-indoors-over-winter
• University of Minnesota Extension — Basil Downy Mildew (symptoms, remove infected plants, Genovese susceptibility, DMR varieties): https://extension.umn.edu/diseases/basil-downy-mildew

• University of Illinois Extension, Good Growing — How to Overwinter Geraniums for Next Year's Garden, Ken Johnson (three methods, 45–50°F bare-root storage, cuttings root in 4–8 weeks): https://extension.illinois.edu/blogs/good-growing/2024-10-11-how-overwinter-geraniums-next-years-garden
• Iowa State University Extension and Outreach, Yard and Garden — How Can I Over-Winter My Geraniums Indoors? (65–70°F, March pruning, 45–55°F bare-root storage, cuttings root in 6–8 weeks): https://yardandgarden.extension.iastate.edu/faq/how-can-i-over-winter-my-geraniums-indoors
• University of Wisconsin–Madison Division of Extension — Overwintering Tender Geraniums, Margaret Murphy (60–65°F, optional root soaking, soaked vs. dry comparison, cuttings as backup): https://hort.extension.wisc.edu/overwintering-tender-geraniums
• Missouri Botanical Garden — How Can I Overwinter My Geranium Plants? (cuttings root in 3–4 weeks, modern basements too warm and dry, soaking roots every few weeks): https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/gardening-help-faqs/question/1374/how-can-i-overwinter-my-geranium-plants

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