Keeping a Rosemary Christmas Tree Alive Till Spring
Check the tree carefully before you buy. If it has water in the bottom of the container, pass. Overwatering is one of the fastest ways to kill this plant. It hales from the Mediterranean where conditions are typically dry rather than wet. Once rosemary starts to decline (read drop all its needles), it's difficult to rescue. The needles on a healthy plant should feel springy and look bright green and plump.
Water sparingly. Wait for the soil in the pot to feel dry to the touch before you water. Sprits occasionally, though. The heat coming from your HVAC system wrings moisture out of the air. If you don't have a humidifier, your indoor air is probably too dry for your houseplants -- including your rosemary bush -- to feel comfortable. Although it doesn't like wet roots, rosemary prefers some comfortable humidity in the air. Buy an inexpensive pump sprayer, and use it to keep the environment around your plant less dry. It also helps to keep rosemary with other houseplants. This creates a more favorable microclimate for all.
Keep it away from artificial heat sources. Artificial heat steals the moisture from the plant and pot as well as from the air. (Actually, it can even suck the moisture out of your wooden furniture and cabinetry.) Place your plant away from heat vents and other heat sources. Also, avoid placing it on warm surfaces like old style television sets. Keep it off the top of your refrigerator, too.
Give the plant plenty of light. Rosemary requires at least six hours of bright light a day. It may be dormant till spring, but it still needs life giving illumination. Place it in your brightest window, but keep it from touching the glass. That cold glass may damage the needles. If this spoils your decorating plans, move the plant into a sunny spot regularly, or buy a grow light for it. Use the grow light when you aren’t in host or hostess mode. In a pinch, you can add a grow light bulb to a regular light fixture. It's a good, cost effective compromise. You can find grow light bulbs at most variety and home improvement stores.
Remove all the fussy stuff. Those baubles on the plant and the decorative wrapper around the pot have to go. The ornaments damage the stems and needles, and the wrapper can cause moisture to pool and kill the roots.
Put the plant outside once in a while. If you live in an area that gets above freezing for a few days periodically throughout the winter months, put the plant outside when weather permits. Think of this as a spa day. In fact, if the plant is looking poorly now, check the Weather Channel and put it outdoors the first chance you get. Be careful, though. Rosemary can't stand freezing conditions. Bring it in again before the temperature drops much below 32 degrees Fahrenheit. You may get a little more outdoor time by keeping the plant in the sunshine but close to a protected area like a wall. The temperature in a protected spot can be a few degrees higher that the published temperature. Invest in an inexpensive thermometer, and check for likely outdoor locations. I have a large commuter rosemary bush that spends summer outdoors and winter inside. I roll it onto my deck five or six times over the winter to get some fresh air and sunshine. It stays near a light colored wall where reflected light and heat keep it happy. This trick really works, so try it.
Repotting isn't a quick fix. If anything, rosemary likes tight quarters -- rootwise. Any problems you're having are more likely water and light related than due to cramped conditions or feeding (fertilizer) shortfalls. Keep the plant in the original pot till spring or even fall of next year. During that time, it will likely require feeding once, probably in late spring.
Photo Rosemary courtesy of Flicker user: Elvert Barnes https://www.flickr.com/photos/perspective/15864017135/in/photolist