One of the most appealing aspects of growing herbs in containers is the gardener’s sense of control. A plant growing in the ground can be subject to high winds, conquering hordes of hungry insects, competition from rampant weeds, trampling by wayward dogs and kids, and all manner of surprise and catastrophe. With pots, one has the ability to provide plants with ideal conditions, at least in some respects.
An obvious advantages of pots over plots is that a ground-bound plant is subject to the limitations of the dirt in any particular region, whether it’s water-clogged heavy clay or sandy soil that drains so freely that it can’t retain the nutrients the plants need.
Dirt is the nuts and bolts of gardening, a basic ingredient that can determine the success, or death, of a plant. Let’s explore the container gardener’s options.
The first rule is, don’t be tempted to just scoop up some soil from the ground for potting an herb, even if it’s good soil. Use a potting mix, whether you buy a bag from the corner discount store or mix your own.
A plant in a pot has needs that are sometimes quite different from those of a garden plant, and you must start with an adequate growing medium. Topsoil or garden loam is the basis for most potting mixes, but other components, both organic and inorganic, are important for optimum plant growth in a container.
A good potting soil provides more than dirt. It should have two seemingly contradictory characteristics: It must drain freely, and at the same time it must be able to retain water. It must find a middle ground between brick-like heavy clay and sand so light that everything washes out.
The most common ingredients in potting mixes, other than soil, include:
• Vermiculite. This is granules of minerals expanded by heat, resulting in a lightweight, highly water-absorbing material that helps keep the potting soil structure open and breathing, as well as free-draining.
• Perlite. This is volcanic glass, which, under very high temperatures, expands until it looks like popcorn. Like vermiculite, it is lightweight and improves drainage, but it doesn’t blend into the potting mix inconspicuously the way vermiculite does, as the white perlite granules can collect on the soil surface. Vermiculite and perlite serve the same purpose in a mix, and both work well, but some gardeners prefer vermiculite for this reason.
• Peat moss. This is highly absorbent organic matter. Like all organic matter, in both plot and pot, it can, over the long term, improve soil texture and water retention, but there are drawbacks. Peat breaks down so slowly that it doesn’t add nutrients to the soil; in fact, it can draw essential plant nutrients, such as nitrogen, from the soil in the decaying process. Also, peat is a nonrenewable resource that is being depleted in some regions of the world. Other forms of organic matter are sometimes preferable.
• Compost. This already decomposed organic matter releases nitrogen slowly and steadily and is one of the best additions to potting soil (or for that matter, one of the best amendments to garden soil). It helps soil retain water and hold onto nutrients, keeps it from compacting and makes it easy to work with. For the gardener of any sort, compost is gold.
• Sand. Horticultural sand, also called sharp sand, is sometimes added to lighten up potting mixes and improve drainage.
For many container herb gardeners, especially those with limited space, buying potting mix by the bag or in bulk at garden centers is the easiest way to go, and many good ones are available. Some come with a slow-release fertilizer added, enough to last one gardening season. I prefer to handle fertilizing myself (because my approach to herb gardening is an organic one and because different plants have different feeding needs), so I would choose a potting mix without the fertilizer added. Buy a potting mix that lists the ingredients on the package so you know it’s providing what you need; some brands take shortcuts to cut costs or add other ingredients solely for a kind of cosmetic appeal.
If you have the space, time and a mind for experimentation, mix your own. You can easily create not only a good general potting soil, but also one that’s as rich or lean as a particular plant demands, or a finely textured one for starting seedlings. You can even save yourself some money this way, particularly if you have a lot of large pots and planters. Home-grown compost, if you’ve got it, can provide the start, and the other components can be bought separately (sometimes even in bulk) and added as desired. If you like getting your hands dirty (and what gardener doesn’t?), making your own potting mix is a satisfying endeavor.
A Good Idea
If you have lots of pots, you’re invariably doing plenty of repotting as your plants grow, and perhaps the question has arisen, what should you do with the old potting soil?
To recycle and recharge old potting soil, put a large bin or trash container in the corner as a collection point over the gardening season for spent plants and old potting mix. Just dump the contents of a pot, roots, dead plants and all, into the bin. When you think about it, sprinkle some water on it and stir it a bit to help it break down and mix together. Otherwise, forget about it, as the decomposing over time of roots and leaves and stems is the recharging process. You can use your bin as the starting point for next year’s batch of potting mix, first sifting through it with your hands to remove plant parts that haven’t sufficiently decomposed and then adding amendments as needed.
This time of year, which in many regions is the off-season, a container indoors near a bright window can be a hospitable home for those tender herbs that won’t survive winter outdoors. Some tender classics that lend themselves to container growing include bay laurel (Laurus nobilis), rosemary (Rosmarinus officinalis), lemon verbena (Alloysia triphylla) and scented geraniums (Pelargonium spp.). Try them; you’ll like them.
Kathleen Halloran, former editor of The Herb Companion, grows potted herbs in Las Vegas, where she is a freelance writer and editor.