Rosemary Producton

Candy Traven

Rosemary is for remembrance. The author wishes to share this information with you in honor and remembrance of Thomas De Baggio, her herb mentor.

A tender perennial evergreen with year-round demand, Rosemary is hardy to Zone 7. With a long history of culinary, medicinal and decorative uses, its numerous cultivars meet many needs. It can be trained into topiary shapes and is especially effective in combination planters and mass plantings.

Propagation
Rosemary doesn't grow well from seed due to poor germination and slow growth. It's more commercially viable when propagated vegetatively. Stock production is a year-round, labor-intensive undertaking. It's more economical to purchase unrooted cuttings from reputable sources with rigid clean stock programs.

Start with a green vegetative tip cutting, not woody or flowering, 1 to 2 in. long. Remove underground foliage before sticking. Stick cuttings immediately upon arrival. There are numerous rooting media that work, such as well-drained soil mixes, Preforma,  Ellepots and Fertiss. Lightly water the rooting media before and after sticking.

In the greenhouse, keep a constant substrate temperature of 72F (22C). Rosemary should receive “medium” mist frequency and duration, as too much will lead to poor root initiation and rotting of the tops. If using vapor pressure deficit (VPD), start at 350 millibars and ramp back 50 to 100 millibars every three days. (Note that all environmental parameters described are for glass houses—plastic coverings and more humid conditions require even further cutback of frequency and durations.)
Rosemary starts to strike roots in 10 to 14 days. It's important to cut back on mist at this time to lessen disease pressures. Pay close attention to the cuttings if it gets sunny or hot, as they desiccate quickly. Do NOT allow them to wilt at any time during the entire production cycle! Once rooted, rosemary will use a surprising amount of water during this period of rapid flushing. Keep it slightly moist at all times.

Rosemary benefits from a tip pinch at three to four weeks after sticking. A finished liner takes six to eight weeks.

Transplanting
Purchasing liners allows you to get what you want when you want it. It allows for more variety and more crop rotations in less time, with less heat. You get more for less, a win-win proposition.

Transplant into a well-drained medium with a pH of 5.8 to 6.2. Four-inch pots finish in six to 10 weeks, depending on variety and season. Pinch as soon as possible after transplanting for better branching. Larger pots, baskets and topiary are best grown from a larger plug or 4-in. pot because rosemary is sensitive to over-watering.

Finishing
Less is best. Fertilize lightly at 125 ppm of 14-4-14 constant feed. During the winter, use nitrate forms instead of ammoniacal nitrogen. Iron chelate is useful if you're unable to maintain the proper pH range. Water management is the key to growing beautiful finished rosemary. Our rule is, “If in doubt, wait until tomorrow.”

Fungal diseases such as root rots and botrytis are common in humid environments. If a plant appears wilted but the soil is wet, get it out of the greenhouse immediately. Rootshield and Plantshield are very effective preventatively for root issues, as is Companion. Rhapsody is effective for botrytis. Milstop works on powdery mildew, and sulfur burners are extremely effective if used daily. The best prevention is good air circulation, ruthless sanitation, proper water management and constant observation and roguing.

The most common insect problems are spider mites and whitefly. BotaniGard, Neem-based products and pyrethrum are all effective. It's important to be aware that the list of approved products is short and likely to get shorter. Currently, we use strictly beneficials and predatory insects for control with excellent results.

Maximize light at all times. Supplemental lighting is not necessary. Temperature range is wide, from the 40s (5C) up. Higher temperatures, while giving faster growth, also lead to softer plants and greater disease and insect pressures. “Lean” growing is always better. Pruning promotes new growth, branching, and a pleasant shape. 

Candy Traven is co-owner of Peace Tree Farm, Kintnersville, Pennsylvania.