Can I winter over lavender here in North Central Iowa?

image from weneedfun.com

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Overwintering Lavender Indoors and Outdoors  By Robin Sweetser
Every spring, I try very hard to resist the siren call of the half-hardy lavenders. I curse the garden centers that offer these plants knowing full well they will not survive the winter in my area! If you’ve succumbed to the lavender allure, here’s how to keep these aromatic gems alive over the winter so you can enjoy them again next summer.
 A fragrant and colorful plant native to Europe and Western Asia, lavender is a sun-loving flower best grown outdoors. Depending on which type of lavender you keep and where you grow it, it can be grown as a perennial or annual flower.
English lavender (Lavandula angustifolia) is the most common species available, and is quite hardy. We grow a variety called ‘Hidcote’ that has dark purple flowers. Despite its name, this plant is not native to England; it stems from the warm, Mediterranean coast of Europe.
English lavender is hardy in Zones 5 and warmer, usually overwintering in the ground outside just fine without any added protection. In an open winter with no snow cover, we may pile a thin layer (1-2 inches) of straw or shredded leaves over them for added cover.
Spanish lavender (L. stoechas) and fringed or French lavender (L. dentata) are much more tender—hardy outdoors only in Zone 8 and warmer. They have to be moved indoors to survive the winter in colder zones.
The good news is that lavenders are fairly compact plants that grow well in containers, which makes moving them indoors and outdoors quite easy. If you are repotting them, don’t use too large a pot. Only give them an extra inch of soil around the root ball. Too much extra soil will just stay soggy, which these plants won’t tolerate.
The soil does not have to be rich, either. Two parts potting soil with one part perlite or coarse sand will give them the quick draining conditions they need. To mimic the alkaline soil of the Mediterranean, add 1 teaspoon of lime to the bag of potting mix before using it in the lavenders’ pots.
How to Overwinter Lavender Indoors & Outdoors
As mentioned above, English lavender is winter-hardy to Zone 5 and may only need a bit of help in the form of a thin layer of straw. Otherwise, lavender shouldn’t need any extra care outdoors. Spanish and French lavenders, on the other hand, are only hardy to Zone 8, and will need to be brought indoors in colder areas.
During winter, the plants want to rest and will not produce much, if any, new growth. They are basically dormant from September until April.
While your lavender is indoors for winter, follow these practices:
•Watering: They need less water in winter, too; wait until the top inch of soil feels dry before giving them a drink. Overwatering will rot the roots and means sure death.
  •Lighting: Although they won’t be actively growing, these plants will still need a lot of light. If you lack a spot on a cool, bright windowsill, try using a grow-light to supplement the natural light.
  •Temperature: During winter, lavenders like it cool but not drafty; the temperature can drop to as low as 40°F (5°C) at night and shouldn’t be warmer than 65°F (18°​​​​​​​C) during the day. This means that you ought to keep them away from heaters that will dry them out and drafty windows that could chill them too much.
  •Fertilizing: The plants may look a little sad, but do not fertilize them until new growth starts in the spring. Unused nutrients can build up in the soil and become toxic.
Even though your plant is resting, the foliage is still fragrant and will smell lovely when you brush against it. The relaxing, anti-depressant qualities of its aroma will be a welcome reminder of summer and help to get you through the long winter ahead.
Come spring, wait until your last spring frost has passed and nighttime temperatures remain above 50°​​​​​​​F (10°C) to plant lavender outdoors again. Also don’t forget to harden them off before exposing them to full sun and cool spring temperatures!
taken from https://www.almanac.com/news/gardening/gardening-advice/lavender-winter-till next time this is Becky Litterer, Becky's Greenhouse Dougherty Iowa beckmall@netins.net