Mistake 2: Starting with the wrong varieties. I recommend you start by trying to grow fresh basil. It is the perfect trainer herb. First, basil grows quickly, allowing you to observe the effects of your care more easily. Second, basil leaves wilt visibly when not watered enough, but recovers well if you water the wilted plant. This makes basil a great ‘canary in the mineshaft’ to help you figure out how much water is enough.
Mistake 3: Watering herbs like houseplants. Instead, water herbs a moderate amount every day. While some houseplants flourish with one solid watering per week, most delicate herbs require moderate and regular watering. This is particularly true during hot summer months. If you have good drainage at the bottom of your pot (at least a drainage hole, possibly rocks beneath the soil), it will be difficult to water herbs too much.
Mistake 4: Not cutting early and often. As a novice gardener, it may seem like your puny little plant just isn't ready for a trip to the barber, but then you will find yourself sitting there wishing for leaves without much success. Again, basil is a great herb to practice pruning. As with all herbs, you want to cut the herb just above a set of growing leaves. With basil, when you cut the plant that way, the originally trimmed stem will no longer grow. However, two new stems will grow around the original cutting, creating a “V” shape (see the photo above, can you spot the Vs?). If you don’t trim basil aggressively, it will continue to grow straight up, and become too tall and top-heavy. Making your first trim approximately 3-4” above the soil produces a nice sturdy plant. Of course you want to be sure you are always leaving a few good sturdy leaves on the plant (see below). As it continues to grow, continue to prune it approximately every 3-4" for a nice solid plant. I like to let it grow for some time and then cut back to within 2-3 inches of the original cut. After only a few early trial cuts, this usually makes for a nice clipping with plenty of basil to use for a pizza.
Mistake 5: Taking the leaves from the wrong place. When you are just starting out it seems to make so much sense to pick off a few big leaves around the bottom of the plant, and let those tender little guys at the top keep growing. Wrong. Leave those large tough old guys at the bottom alone. They are the solar panels that power your herb's growth. Once your plant is big enough to sustain a decent harvest, keep on taking from the top, as you have been when you were pruning. That way you get all those tender new herbs that are so tasty, and your plant gets to keep its well developed solar power system in place. Plus, if you pluck from the base and leave the top intact, you get a tall skinny plant that will flop over from its own weight (and yes, I know this from experience). When you pluck from the top, instead of clipping off just below a pair of leaves, you want to clip off just above a pair of leaves. It is a bit counter-intuitive as a novice, but trust me it works. The place where the leaf joins the stem is where new growth will occur when your plant sends off new stems in a V.
Mistake 6: Letting your plants get too randy. If you are pruning regularly, this may never become an issue, but unless you are growing something for its edible flowers, be sure to cut back herbs before they start growing flowers. My friend once brought me to her backyard garden and pointed, frustrated, at her wimpy, small basil plants. "I just keep tending them, but they don't even produce enough leaves to put on a salad!" she lamented. I pointed to the glorious stalk of flowers at the top of each plant, "That's your problem" I explained. Because herbs are kind of like college boys: if you give them half a chance, they will focus all their energy on procreation and neglect growth. If you want leaves, keep cutting off the little flower buds whenever you find them (see photo above), and it will encourage your plant to focus on growing more leaves.
Mistake 7: Using tired soil with no nutrients. Tired soil that has been sitting in your garden or lawn for ages often looks grey and a little depressing. Would you want to grow in that stuff? Give your plants a dose of the good stuff and they'll thank you for it. I grow my herbs in a combination of potting soil, used coffee grounds (with a near-neutral PH, available for free at Starbucks), and organic compost. If I have some on hand, I also throw in crushed egg shells. Those without access to compost (and no deep commitment to organic growing) may find Miracle grow useful. My momma swears by it for tomatoes. A diluted solution of Miracle grow occasionally can help many herbs flourish.
Mistake 8: Getting in a rut. There is an element to passion about herb gardening. In order to be good at it, you need to feel rewarded. So don't stick too long with one or two herbs just because they work. Branch out to a few other basic herbs that you will use regularly in your kitchen. There are few things more rewarding as an urban foodie than being able to pop out to the fire escape to clip fresh herbs to use in my cooking. Once you have become comfortable with basil, I recommend moving on to try growing oregano, mint, rosemary and thyme. All are regularly useful herbs in the kitchen, and all are relatively easy to grow. You will notice that rosemary cleaves after cutting in a somewhat similar way to basil, but grows much more slowly, so the effect is difficult to notice. Some plants also respond to clipping by throwing out more full leaves at their base. I have long wanted to grow cilantro but have not had much luck with it.
Mistake 9: You mean there's more than one kind of mint?When choosing herbs, read the label carefully. For example, there are two main varieties of oregano: Mediterranean and Mexican. Mediterranean oregano is the more common variety, and what you likely own if you have conventional dried oregano in your cupboard. I have Mexican oregano growing on my back fire escape. I love Mexican oregano in spicy dishes, for making beans from scratch, and often use it in tomato dishes where I don't want the flavor to seem too much like marinara. Similarly, there are many different kinds of mint. You don't want to be thinking of the pungent spearmint plant and accidentally take home the much more subtle (and not mojito savvy) applemint by mistake.
Mistake 10: Feed me Seymour! If you are planting in soil instead of pots, take care that your cute little herb seedling doesn't become a giant plant that takes over your garden. A word of warning for oregano and mint: both can be voracious growers. If you are planting outside in a garden, rather than in pots, you may want to consider potting these herbs and then burying the pots in the ground. This will add a measure of control to the root systems of these herbs, which can otherwise take over a garden and strangle nearby neighbors. When in doubt, check out wikipedia, they usually are careful to point out which herbs are in danger of overwhelming your garden.