How to Overwinter Rosemary in Pots and in the Ground in Colder Zones

Rosemary, an evergreen drought-tolerant herb, can thrive in zones 8 through 10, though varieties known as Arp and Hills Hardy (also called Madalene Hill) are known for being extra hardy even down in zones 6. Central Illinois gardeners sometimes attempt to overwinter rosemary outdoors by placing it against walls for protection before applying a thick layer of mulch after frost has hit.

Planting

Rosemary can thrive both indoors and out. To thrive successfully in both settings, it requires full sun with good drainage; preferring slightly rocky, sandy or loamy soils over sites that are too clayish or compacted. Overwatering could result in root rot. Rosemary also thrives best with adequate air movement around it – placing two-to-three foot spacing between plants will prevent fungal diseases that cause discolored leaves or wilted plants from appearing.

Woody stems of this herb make it attractive year-round, yet can also be pruned into shape with sharp and sanitized tools for pruning. When doing so, remove no more than one-third of a plant at one time so as to avoid overly woody or tangled stems and growth patterns. In late winter, prune the tops to promote bushier growth as well as eliminate spent flower heads from your herb garden.

To propagate rosemary from seed, collect seeds from an established plant and sow them in spring. For cuttings, clip 2-1/2-inch stems from new growth and dip them into hormone rooting powder for quick rooting (see Propagating Rosemary). Once rooted, transplant them into 3-1/2-inch pots; during their growing season add an organic fertilizer for faster new growth; during fall add insulating mulch as a buffer against harsh winter temperatures.

Watering

Rosemary (Rosmarinus officinalis) is an easy-care herb, ideal for mild climates. Not only can it serve as an attractive ground cover but its flavorful leaves can be used in cooking as well as aromatherapy sessions. Furthermore, rosemary has many medicinal uses including relieving heartburn symptoms and soothing skin irritated by eczema.

Rosemary thrives best when planted in sunny locations with well-draining soil, such as adding sand or perlite to native earth to improve drainage, as this is essential for healthy plants. Heavily mulching around its base may also protect it against cold temperatures.

Root rot, a fungal disease affecting rosemary plants, is the primary issue when growing them. Preventative measures include watering the soil properly to promote drainage and avoiding overhead irrigation as these will both aid drainage.

Pruning and ongoing care can help a rosemary plant thrive. Regular trimming helps ensure its size remains manageable while eliminating leggy stems. Rotation weekly ensures all sides receive sunlight. Keeping rosemary indoors requires proper ventilation in the planting area as powdery mildew may form otherwise.

Some rosemary varieties, like Arp and Hills Hardy, can withstand zones 6 through 5, making them suitable for gardeners living in cooler regions. To overwinter rosemary successfully in containers, bring them indoors after frostfall has occurred and give them a sunny spot away from drafts for optimal care over winter.

Mulching

Rosemary is an herb with excellent cold hardiness, typically surviving the winter outdoors in USDA zones 7-10. To increase their odds in colder environments beyond these, it’s wise to mulch rosemary plants as protection during the cold months, as this helps reduce weed competition and shield roots from freezing temperatures. Regular pruning also encourages bushy development and prevents leggy stems.

When growing rosemary in containers, use one that is at least as deep as the height of the plant and features drainage holes. A mixture of soil including perlite or pumice will enhance drainage and help aeration; Rosemary thrives best in soil that ranges between moderately acidic (pH 6.0 to 7.5) and slightly alkaline (pH 6 to 7), as poorly draining soil inhibits oxygen supply to its roots and may even lead to root rot.

Rosemary plants require light fertilization; however, it’s essential not to overfertilize. A slow-release balanced garden fertilizer should be applied during spring and summer. Fertilization should stop two months prior to your average first frost date for maximum benefit.

Temperature

Rosemary cannot tolerate cold temperatures; therefore if your winter temps dip into single digits, you will need to move it indoors and plant in a pot with at least as much above-ground growth as the one used above and a wide enough base so there is at least an inch between its roots and sidewall of pot. Furthermore, ensure it contains drainage holes for proper water drainage and fast-draining soil, such as organic cactus soil or worm castings for best results.

When growing rosemary indoors, water the soil every week or two and mist its foliage regularly. Wet feet don’t benefit the rosemary either – when temperatures heat up a little bit you may need to let its leaves absorb moisture from the atmosphere instead.

Some gardeners have successfully grown and overwintered rosemary outside of its zones with careful protection, such as using a cold frame structure that traps heat and reflects light; or applying a layer of gravel mulch (but no too thick!) over your herb plants in cold weather. You could also try one of the extra-hardy cultivars known for surviving in zones 6ish such as Arp or Hill Hardy (Madalene Hill). These hardier varieties could even withstand central Illinois’ extreme winter weather with some help from gardeners!