• Air. Your herbs will thrive in a temperature between 65° to 70°F, about what is comfortable to you. Avoid rooms that are stuffy and have stale air. Herbs like fresh, moving air but not drafts; humidity is best around 50 percent.
• Soil. For your container potting mix, forget about soil. A soil-less medium of one part sphagnum peat moss and one part perlite makes a good mixture for herbs. If you prepare your own mix, add 3 to 4 tablespoons of horticultural lime per quart of mix; peat can be quite acid and the lime sweetens the mix. Stir ingredients while dry and dampen the medium before planting. Soil-less media with natural ingredients, but without soil, have been tested on herbs and found to be superior to other potting soils. For years we have used Pro-Mix BX, a commercial soil-less medium, with excellent results.
• Water. Watering is not as tricky and mysterious as you may have been led to believe. Here are a few general rules which might improve your green thumb: Don't let the pot sit in water and drown the herb's roots. During warm weather and rapid growth, plants are more tolerant of water. When the air is cool and light is poor, go easy with water and allow the surface of the soil to dry between watering. Water temperature should match air temperature. A fan moving air around and over your potted herbs will help dry the growing medium.
• Pots. Containers come in many sizes, shapes, colors and materials. I like plastic because it is light and cheap. Plants do not dry as quickly in plastic as they do in clay pots which can be a disadvantage during winter. Don't worry about stones or broken crockery in the bottom when the pot has lots of drainage holes; the stones actually hinder drainage and are a bad idea. Pot your herbs in a container 2 inches larger than the one it is transplanted from. Don't put a small plant in a huge pot, the roots cannot use all that moisture and they are likely to rot quickly. Because plants grow at different rates, planters with several different types of herbs will need careful attention; it is sometimes better to use the planter to hold individual pots which can make individual transplanting easier. You can keep your plants smaller by leaving them in small pots, but this restriction of growth means less foliage and it can harm the plant. When roots begin to fill the pot and circle its sides, it is time to transplant. Yellowing leaves or shedding leaves sometimes indicates the plant is pot bound.
• Light. Most herbs need 5 hours of full sun for optimum growth. Only a few herbs will grow well without direct sunlight. Don't despair if you lack a south facing, sunny window. Herbs will often adjust to less than the best conditions. A fluorescent light garden is one way to give your herbs and other plants near perfect light conditions. Commercially available 'Grow Lites' can be used but are more expensive. Fluorescent tubes should be no more than 3 to 5 inches above plant tops. Use 4 cool white tubes for each 10 inches of table width. Lights can be used to supplement natural sunlight. Use a timer to provide a total (sun and fluorescent) photo period of 12-14 hours.
• Food. It's better to give your herbs a little food often (every week at half strength, for instance) than a lot all at once. A slow release fertilizer like Osmocote 14-14-14 works well. If your pots are small and you like liquid fertilizers, choose a 10-10-10 or a 20-10-20 formula. Keep in mind that when you water more often, you should also feed your plants more often. Organic fertilizers such as fish emulsion are excellent for soil-less potting media.

Containers are likely to be home to many of the rosemaries in your collection because so many varieties are not winter hardy. Fortunately, rosemary performs well in pots. If you must bring your rosemary inside during winter, grow it in containers year-round rather than dig a plant from the garden and pot it for indoors. Pots made of clay or plastic are appropriate; the choice of which material depends on the season. Clay's porosity permits more rapid drying of the growing medium in the pot. This choice may have an advantage during low-light periods when successful watering becomes difficult. However, plastic's ability to prevent rapid moisture loss is an asset in hot, sunny weather. Allow your esthetic sensibilities to make the final choice.

Almost any disease-free growing medium with a good supply of perlite or similar aggregate is suitable. My own favorite is a standard commercial mix called Pro-Mix, available at the greenhouse. This mix contains perlite, vermiculite, peat moss, lime and a small amount of fertilizer. If you mix your own, add equal parts of sphagnum peat and perlite and a tablespoon of lime for each quart of mix. Time-release fertilizers work well with this type of medium or you may choose to use a liquid nutrient solution. Either way use a formula that is similar to 20-20-20 or 20-10-20. Apply liquid fertilizers after every five to ten times you water.

Rosemary does best in full sun so try to put your plants in the sunniest window you have or in a spot outside flooded with direct sunlight. Rosemary plants are particular about how they are watered. More plants are lost from over watering than from under watering. When grown indoors or during the short, sunless days of winter, allow plants to dry nearly to the point where they wilt. However, if you permit the plant to stay in a wilted, droopy condition for too long it will not revive when watered. During winter do not water on heavily overcast days, unless the plant will wilt otherwise. Watering at such times could cause the plant to die within a few days from its inability to get rid of the water that is filling the tiny air pockets in the growing medium. When leaf-tips or whole leaves turn brown and fall off, the plant is suffocating from too much water. Hold off on watering immediately. Leaves do not turn brown and fall off because of too much sun or too little water; lack of humidity does not cause this condition either. There is no need to mist rosemary plants. In fact, too much humidity may cause fungal diseases.

Here are some warning signs for which to watch: Yellowing leaves at the base of the plant often means the rosemary is root bound. If the condition is allowed to continue the yellow leaves drop, the plant's growth will slow and eventually most of the leaves will shed before it dies. Check the root ball when you notice yellowing leaves. If the root ball is covered with tightly circling roots, it should be repotted to a container three or four inches larger.

Not a lot can be said for sure about rosemary hardiness. One thing is certain: few of the many varieties of rosemary that exist have been given extensive hardiness tests. Five rosemary varieties show promise to beat all but our most severe winters: 'Arp', 'Hill Hardy', 'Salem', 'Nancy Howard', and 'Dutch Mill'. I must confess to constant surprises when it comes to hardiness. 'Miss Jessopp's Upright', for instance, was at one time sold as a winter hardy variety under the name 'Trusty'. It worked well for some gardeners as far north as Pennsylvania, but it was definitely not hardy for everybody or for every site. Then again, 'Tuscan Blue', about which nobody has made any hardiness claims, has survived mild winters (about 10°F) here in pots above the ground, something that wouldn't be expected of even the hardiest rosemary.

There are many factors that influence hardiness besides severity of cold. Soil drainage may be the most important. Plants that have roots sitting in water or are constantly drenched by winer rain or melting snow stand less chance of living through even a relatively mild winter. Wind also greatly affects hardiness. A less obvious but important factor is early planting. Plant before June 1 so plants have time to get firmly established.

Our gardens are located in a border area of hardiness for rosemary and individual locations vary so it's worth trying almost any variety in a particular site. The time to take protective measures against cold is in early winter. A protective spray of Wilt-pruf will lessen the chances of leaf dehydration from cold, sharp wind, but our winter can also bring heavy snows or ice storms which cause branches to break. Polyethylene sheeting tied around rosemary plants gives branches support and provides good winter protection. Cut a piece of poly long enough to go around the outside of the plant at least once; the poly should be as wide as the plant is tall. Wrap this sheet--it can be clear, white, or black--around the plant, being careful to leave the top open. Tie the poly in place with soft string and tight enough to draw the branches up slightly to give support against the weight of the snow and ice. Burying the plant in organic mulches, a common method for protecting deciduous shrubs may also help, but can foster fungal diseases on evergreens such as rosemary and is not a recommended course of action.

Rosemary plants are evergreen and if spring finds them without leaves, they are probably dead. It's prudent to wait well after spring's warm weather has commenced before making a final judgment about your rosemary.

• Pruning for shape. Some pruning will be required to keep any rosemary shapely, but the variety's growth habit dictates how much. Rosemary plants can be pruned to almost any shape but the most popular are globes and columns; the variety sometimes lends itself to one or the other shape, but rigorous pruning can overcome any plant's inclinations. The best time to prune for shape is when the plant is in full growth (in our area this is spring and summer); this will provide the plant enough time to recover before the rigors of winter. Remove the amount of stem necessary to create the shape you desire but try not to remove more than half the stem length. Leave some green leaves on the branch that is left. Pruning for shape is essential for rosemary grown into topiary forms. During periods of optimum growth such forms may need pruning every few weeks. When light levels are low indoors, pruning is useful to keep stems from becoming leggy.
• Pruning for health. Winter damage and disease are another reasons to prune. Dead wood caused by winter cold should be removed in early spring. Cut damaged stems back to green leaves or if the stem is dead, remove it. Fungus disease sometimes attacks low-lying branches and the inside of the plant where air circulation and light are poor; this is a particular problem in humid climates or when there is an unusual amount of rain. Lower branches that have dead leaves on them should be removed so that air can circulate under and through the plant to dry dampness. A mulch of several inches of sand or pea gravel dries quickly and radiates drying heat into the plant and is helpful to control diseases.
• Pruning for use. The most enjoyable pruning is for use. Snip branch tips to use when needed; no special method or procedure is necessary and it may be done at any time of year. Fresh growth, rather than hard, woody stems is best. Performed shrewdly, this pruning will shape your plant and keep it healthy.
• Root pruning. Pruning the roots of container-grown plants is a last resort; it revives and reinvigorates root bound plants when larger pots are unavailable. Root pruning is best performed in mid-spring after the plant has been outside for several weeks and soft indoor winter growth has been removed or has stiffened. After the plant is knocked from the pot, take a sharp knife and remove the bottom third of the root ball; then slice several inches from the sides. Add fresh growing medium to the container and return the plant, being careful to work the medium around the edges of the root ball. The root-pruned plant is likely to show some stress in the form of wilting at this time. A protective spray of Wilt-Pruf will help less foliage dehydration. Keep the plant in a spot sheltered from direct sun for a week before returning it to a sunny exposure.

Although many gardeners think of rosemary as a single plant, there are numerous named varieties- more than three dozen and growing. Many of the differences between these varieties rest on subtleties that sometimes escape the untrained eye or nose, but they are important and are worth cataloging.

The typical growth trait of rosemary is unintentionally sprawling, often wildly windswept and twisted. Horticulturally, it is tagged as semi-upright. Yet, there are varieties that are quite procumbent ('Prostratus' and 'Mrs. Howard's Creeping') and others that are rigidly upright on thick stems ('Gorizia' and 'Tuscan Blue'). Other varieties are open with leaves spaced far apart on their stems ('Lottie DeBaggio' and 'Miss Jessopp's Upright'). Still others are compact with crammed leaves ('Herb Cottage' and 'Blue Boy'). Yet others have large, flat leaves that hardly resemble the typical rosemary ('Gorizia').

Leaf color and aroma differ among varieties, as well. Most rosemary leaves are green ('Joyce DeBaggio' sports variegated green and gold leaves), but even amongst the green there is much variation in hue.

Little attention has been paid to rosemary's ornamental qualities in our area because so few varieties are winter hardy. Flower color is a major ornamental difference. Small blossoms cluster along stems, but the colors range from the lightest to deepest blues, whites, and pinks. There are differences, also, in seasonal flowering. Frequent pruning for use often leads to plants barren of flowers. Climate and day length play important roles in when rosemary blooms as well. Little research has been done on what triggers rosemary flowers. Not much can be said for certain about what makes a rosemary bloom except that some plants can be counted on to bloom regularly while others need some stress and woodiness to their stems before bursting forth.

The plant's aroma, the most important characteristic when it comes to using the leaves in the kitchen, almost defies categorization. The depth and subtlety of the fragrances of rosemary varieties are difficult to describe. Some are robust and nose clearing ('Joyce DeBaggio' and 'Arp'), while others are mild and filled with subtle, flowery, spicy undertones ('Tuscan Blue' and 'Gorizia'). In the kitchen, these aromatic differences may alter how much of a particular rosemary will be used. More subtle varieties may be appropriate for use with vegetables, while the more assertive types can stand up to a beef roast.

The combination of shape, color, and aroma make each variety enchanting, unique, and worth possessing.

Your plants have been carefully grown in my greenhouses and selected for form and vigor. Before you transplant them to the garden they should be conditioned to ready them for outdoor survival by a process horticulturists call 'hardening off'.

When you bring your plants home and outdoor temperatures are above 40°F, keep them outside in a partly sunny spot (direct sun can sometimes burn tender plant tissue) protected from wind. Bring the plants inside if temperatures are expected to drop below 40°F. After four to seven days of this regimen, the plants should be hardened enough to transplant outside. Less water should be given the plants during this treatment, but care should be taken to keep the plants from wilting. A weak solution of liquid fertilizer, applied to the plant at the time of transplanting, will also help get it off to a good start.

Early transplanting calls for vigilance by the gardener and attention to weather forecast. Danger of a frost or freeze means measures must be taken to protect the young transplants. Poly spun row covers (like Reemay) will provide up to 4°F of protection. Wall O' Water is an excellent choice for protecting tender plants as well as warming the soil prior to planting. Properly installed, the Wall O' Water can give up to 10°F of protection. Effective, home-made devices can be constructed from old plastic milk containers or styrofoam cups with the bottoms removed. An old sheet or blanket will also do in a pinch.

Although no special equipment is necessary to harden off your plants, a cold frame will be helpful. A cold frame is nothing more than a protective structure with a glass or plastic top that will open and shut. Sides may be of wood, masonry, straw, bundled newspapers, or poly sheeting stapled to a wooden frame. The top is usually slanted (usually towards the south) so that it will catch the sun and drain rain water away from the structure. The cold frame protects young seedlings and transplants from the ravages of spring wind and unsettled cold weather. Seedlings are hardened off for a week or two in such a structure to stiffen their stems and adjust them to temperature fluctuations that did not exist indoors on your window sill, under your grow lights, or inside the greenhouse, where conditions are ideal and encourage soft growth.