Rosemary is a beautiful, fragrant shrub that is common in both ornamental and herb gardens. It doesn’t need a lot of water, it produces pretty little flowers, is attractive to pollinators, deer and rabbits usually leave it alone, and it is a pretty low maintenance shrub. Branches can be used in cut flower arrangements and table decorations, leaves can be used in cooking, potpourri, or used to make essential oils. It can be grown in the ground, or in patio containers, and it can be grown in combination with both flowers, and other herbs.
The big questions is whether or not there is a difference between ornamental and culinary rosemary. The short answer is not really. The longer answer is a little more nuanced. Cultivars that are typically used as culinary rosemary grows more upright. This makes the new growth (Best for using in cooking) the easiest to harvest. It also tends to have higher oil content. Rosemary cultivars that are better for landscaping tend to have more side branches, or sometimes even grow almost flat like a ground cover. The leaves of these types tend to be a little tougher, and don’t always have a high oil content. That being said, it is all the same species Rosmarinus officinalis. So go ahead and use whatever rosemary you want when cooking.
A small word of warning when buying rosemary plants: Pesticides and other chemicals have labels on them that specify whether they can be used on food crops. If a rosemary plant is labeled as an ornamental plant, it isn’t a good idea to eat it, as it might have been treated with a pesticide not intended for use in food crops. However, if the rosemary plant is labeled as an herb, then you can be sure all chemicals used to grow that plant were approved for food crops. Commercial growers with pesticide application licenses are very careful about following the rules of the chemical labels. But what if you already have a rosemary plant in your yard, and you aren’t sure how it was grown originally? Most systematic chemicals that might have been applied to an ornamental plant will be gone after two years. (This is the very upper end of the lifespan. It is probably gone well before that, but with this sort of thing we want to exercise an abundance of caution). So if your plant has been in the ground for more than two years and you have not applied any systemic pesticides to it, you are most likely fine to use the leaves in food.
The care of rosemary is almost identical if you wish to use the plant for ornamental or herb purposes.
Climate: Rosemary is a Mediterranean plant. It likes warm, dry weather. It is not frost tolerant. It will do best in USDA zones 8-11. If you live in an area with colder winters, you can grow the rosemary in containers and protect it during the winter. Or you can treat them like an annual and replant them every year. In the proper climate zone, upright rosemary can get to be a very large shrub, up to 6 feet tall. So give it plenty of room in your garden, or stay on top of pruning.
Sun: Rosemary loves its sun. It needs at least 6 to 8 hours of sunlight a day, but will tolerate much more.
Soil: Rosemary is a little susceptible to root rot, so it really needs a well-drained soil. It will tolerate poor soil, but will look better with a loamy one. Add compost to help with nutrients and air space.
Fertilizer: Here is the big difference between ornamental and culinary rosemary. If you are growing the rosemary as an herb, you will want to fertilize it starting in early spring and following up with a few more applications during the warm season. Use a balanced fertilizer for veggie and herb gardens, and follow the instructions on the container of whatever one you choose. Do not fertilize it after late summer, as you want to keep it nice and hardy for the winter. If you are growing it strictly for ornamental uses it usually doesn’t need any supplemental fertilizer. If you’re growing rosemary in containers for ornamental purposes, you can fertilize it once a year in the spring. If you’re growing it in containers for culinary purposes do it a few times, but be careful not to overdo it. Pushing too much new growth will make the plant weak and more susceptible to pests.
Water: Rosemary is pretty drought tolerant. It really doesn’t need much water, and it likes to dry down between waterings. In an herb garden, give it a little drink on very hot, dry days. The plant will survive the hot, dry days just fine, but giving it a little boost of water will keep the foliage softer and more lush for better flavor and texture.
Pests and Diseases: As mentioned above, rosemary can be susceptible to root rot. Be very careful applying fungicide to edible plants. Only use a fungicide with a label that says it can be used for herb crops if you plan to use the leaves for cooking. If it is strictly an ornamental plant, then you can use whatever fungicide you want, BUT make sure everyone knows that the rosemary isn’t for eating. It is best to try to avoid the problem by allowing the soil to dry down between waterings. Same goes for powdery mildew treatment.
Rosemary is often an attractive plant for spittlebugs. These bugs are annoying and do suck the sap, but there are rarely enough of them to do any harm to the plant. Aphids can also be attracted to rosemary. The best remedy for both of these pests is simply blast them with a stream of water. Do this in the mornings so the water dries before nightfall. You really have to be careful with pesticides on edible plants. If you do choose to spray something on these pests, read the label carefully. Especially look at the harvest time. If the chemical says not to eat anything sprayed with it for three days following application, then don’t eat it before that three day period is up. And again, make extra sure that the label says it is ok to use on herbs. In most cases, it's likely that you won't need to treat the plant at all.
Maintenance: Ornamental rosemary needs very little maintenance. You can prune it to whatever size you want, or not. Many people plant it on hillsides and just leave it. For culinary rosemary, the more you prune it, the bushier it will get, and the more stems you will get for new growth which are the best for eating.
Rosemary is extremely versatile, and many people like to plant rosemary for the dual purpose of a low maintenance landscape shrub and a culinary herb. It is really delightful to walk out to your garden and harvest the few sprigs you need to flavor your food. It is so much better than buying a whole bunch at the grocery store that then spoils in your fridge before you use it again. Since growing rosemary is so easy and the plant lives well in mild climates, why not plant at least one, enjoy its beauty and fragrance in the yard, and never waste store bought rosemary again.