Growing In Containers
Those who have gardens may still want to grow some plants in containers to brighten up a deck, patio, or the front stoop. If you think you can't garden because yard space is limited, container gardening offers you new options. Many herbs grow well in containers, but growing in a pot is unlike growing in a garden. Special attention must be paid to some of the things we take for granted with plants growing in the garden
- pots—what they are made of, how big they are, and how they drain
- potting mix—it has to be light and contain nutrients needed by the plants
- location—sun, partial shade, sheltered
- planting—special needs for potted plants
- watering—how much and how often
- fertilizing—how often and what fertilizer
- pruning and training—which plants, how, and how often
Two excellent herbs to grow in pots are African blue basil and Fernleaf dill, which was actually developed to be grown in a pot. You'll find scented geraniums and alpine strawberries good in pots, too. In fact, alpine strawberries are the best strawberries for pots because they don't put out runners and they have a smallish rootball.
Here are a few other tips about specific herbs:
- Mediterranean herbs such as lavender, sweet marjoram, thyme, and rosemary like a sandy soil.
- Sweet marjoram and thyme do well together.
- Rosemary, lavender, lemon verbena, and sage make fine single specimens in a 9½" to 12" pot.
- Parsley and dill have longish taproots and will do best in a deep pot.
- Mint likes it wet and shady.
- Coriander and parsley like a bright spot without direct sunlight and like it cool and wet.
- The following herbs are suitable for hanging baskets: In sun-creeping thymes, prostrate rosemary, and ivies. In shade-pennyroyal and mints.
- If you have an itty bitty space for culinary herbs, consider a window box with parsley, chives, rosemary, creeping lemon thyme, and basil, if it is a sheltered spot. Calendula or nasturtiums add a bit of color and can be eaten in salad.
You will want the pot you choose to be attractive as well as functional. Clay pots are beautiful, but they are more porous than plastic and will dry out more quickly. Plants in clay pots will have to be watered more often. On the other hand, if the type of herb needs to dry out before re-watering, a clay pot is just the thing for that plant. Some clay pots are glazed. The glaze creates a nonporous finish that slows evaporation. Also, nowadays there are pots of beautiful, lightweight materials that are made to look like clay. They weather well and retain water.
High temperatures of the midday summer sun beating down on the pot will burn plant roots so dark colored pots are better than light ones that allow roots to absorb light, causing stunted growth. Plastic pots are available in darker colors, are inexpensive, durable, and lightweight. They come in many sizes and some have built-in saucers. If you do not like the looks of it, you can disguise it by slipping it into a larger, more decorative pot. Plastic loses water more slowly than clay, and soil temperature varies less. What it boils down to is that plastic makes less work with less chance of running into problems, but if you are a stickler for fashion, clay pots require more diligence on your part to keep your plants thriving.
Planters that are wooden boxes, tubs, or barrels fit well in almost any setting. Look for cedar and redwood for longevity. One of the best herb containers you can use is an old-fashioned half whiskey barrel. It gives you plenty of space for a collection of herbs, good drainage, dark color, little evaporation, and the folksy ambiance you may want to keep fashionable.
Hanging baskets are another container possibility. They can be made of wood, wire, clay, or plastic. Some come with holes or hooks in the rim. Wire hangers are usually lined with sphagnum moss or coir, and then filled with potting mix and plants. These baskets never have drainage problems and work well in almost any design scheme.
Good drainage is just as important in containers as in the garden. Holes in the bottom of pots are a must, and the pots need to be set on an open, porous surface. A tray filled with sand or gravel makes an excellent "bed" for your pots. If you have the perfect pot and it has no holes, drill them yourself. An 8" to 12" pot needs a 1/2 " hole. For an extra large pot, drill four to five ¾" holes. Use an electric drill with masonry or carbide bits for clay pots. And now I'm going to dispel one of the great myths of gardening in containers. Broken crockery or pebbles in the bottom of the pot does nothing to improve drainage. When the roots hit the pebbles, they dry right out and the pebbles may even block drainage.
Don't crowd pots with too many plants. They can get stunted, and crowding can promote diseases. Depending on the contents, you may need to step up to a bigger pot size during the season.
Once you have chosen your pot, you need to consider the potting soil to use. Garden soil alone is not a good choice because it packs down, forming a dense mass that roots cannot penetrate. There is not a bagged potting soil I've tried that didn't need to be "beefed up" for container plants. It's a good idea to start with bagged soil because then you know you aren't starting with weed seeds. But I get out the wheelbarrow and mix up my own recipe of perlite, vermiculite, coarse bark mulch, and sand with the bagged soil. A couple of handfuls of each plus some composted manure or old compost from the bin and I know I've got a mix that plants will thrive in. What is important is to keep it light and provide all the nutrients the plants need.
I recommend either of the following mixes:
1 part garden loam, 1 part potting mix (store bought) and 1 part perlite.
6 quarts peat moss, 1 quart compost, ¼ cup bonemeal, ¼ cup 5-3-4 fertilizer, 1 TBS lime, 2 quarts perlite.
For best results when gardening in containers, choose plants that suit your climate, give them the right light, and protect them from strong winds and intense heat and cold. One would think that the long sunny days in New Mexico would be ideal for growing a wonderful container garden. Not so. When I lived there, I had to deal with intense heat, which could burn the plants to a crisp in a matter of hours. Plants need sun, but remember they are sensitive to the intensity of sunlight. Some like full sun all day, some morning sun, some do best in partial shade and others full shade. Think of partial shade as shade under a lacy tree and full shade as building shade or shade under a heavy canopy of leaves. Strong-stemmed plants may not mind harsh wind, but plants like basil have large, soft leaves and need to be protected from strong winds. And it's a good idea to keep plants away from structures that reflect strong heat. Lastly, in the fall, guard against frost by covering your plants or bringing them in. If plants freeze, shift them to a cold, not freezing, spot where there is bright light and let them thaw slowly. They may revive.
Before taking a plant from any nursery container, water the soil thoroughly—moist soil clings to roots, helping to hold the rootball together. To remove a plant from a pot, invert the pot and tap it gently on the bottom. If it doesn't come out, run a knife around the pot's inside edge and try again. Check the root ball after it comes out. If the plant was pot bound, score the roots lightly with a sharp knife, and loosen the roots by teasing them with your fingers. Put a cushion of moist soil mix in the container, enough so that the top of the rootball is about 1" below the pot's rim. Position the plant in the middle of the container and fill in more moist soil mix around the plant's sides, pressing it in firmly so as to plug air holes. Do an initial watering from the top, or put the pot in water and let the soil seep up the moisture. Set the pot in a spot protected from the sun and wind for about a week. The plants should be repotted when you see roots coming out of the bottom drainage holes.
Container plants have only the soil in their pots to draw on for water. They require more frequent watering than garden plants. Some will need to be watered every day; others will want to dry out somewhat before being watered. For the latter, see that the surface of the soil has dried, then you can check the moisture level by pushing your finger an inch into the soil to feel the level of moisture. If it's dry an inch down, it's time to water.
Lighter soil mixes will dry out more quickly than heavier ones. If you see the soil is not absorbing water and is running right through the pot, let them sit in a tub of water for an extended period of time to let the soil absorb the water. If this does not solve the problem, you may want to repot into a larger container. During hot, dry, windy weather, actively growing plants may need to be watered several times a day. The best time of day to begin watering is very early in the morning before the wind stirs and the temperatures rise. Many people believe that watering in the evening is best, but you run the risk of perpetuating fungal diseases when plants retain moisture all night long. If temperatures remain high at night, an evening watering is a good idea, but when they dip several degrees, cool, wet conditions may pose a problem.
Don't rely on rain to provide enough moisture. Do the finger test to see if plants received ample rainfall, and don't forget to water plants you have under eaves or overhangs, even in rainy weather. Chances are, they are protected from the rain, and if no rainfall reaches them, they will suffer from drought.
How much water is enough? Water until you see water coming out of the drainage holes. If water is not draining, your soil may be too heavy. Check to see that the drainage hole in not blocked. Repot if necessary. If the weather is rainy day after day, do not let your plants sit in a saucer full of water because eventually, this will cause them to drown and roots will rot. If your pots are drying out too quickly, you can mulch pots as well as gardens. Also, consider growing ground covers in the pots—creeping thymes, chickweed, any low growing plant will do. These act as natural mulches, which will retain water and moderate soil temperatures. If you are going away for a few days and can't find a plant sitter, you can buy special nylon wicks or make your own. Make them from thin cotton clothesline. Push one end 1 to 2 inches into soil in the pot; put the other end into a wide, water-filled reservoir. Soaker hoses on a timing system work well, too.
Because of all the watering you need to do with container plants, nutrients leach out pretty fast. As a general rule, fertilize regularly from spring through summer when the plants are actively growing, every two weeks. Stop in late autumn and winter. If you are using potting soil that contains nutrients, begin fertilizing 4 to 6 weeks after planting. But if it is not "enriched", begin fertilizing right away. You can buy fertilizer in three forms-dry, liquid, and timed release. Both dry and timed release fertilizers release nutrients over a longer period of time, so you apply them less often. When using dry, make sure the soil is wet, otherwise the fertilizer can burn the roots and foliage. If you apply too much, you can leach it out with water. Be sure the fertilizer you buy has trace elements as well as a balance of nitrogen, phosphorous, and potassium. Complete fertilizers include nitrogen (N), phosphorus (P), and potassium (K). The ratio of these three are given on the package label, such as 5-10-10 or 16-10-4. High nitrogen fertilizers (the first number in the ratio) encourages lush leaf growth. High phosphorus fertilizers encourage plants to develop strong roots and prolific bloom. Beware of over-fertilizing. I think of these high potency fertilizers as "steroids". If your soil mix is good to start with, a mix of fish emulsion and seaweed is adequate. I'm an organic type person, so I mix up my own compost tea, comfrey or stinging nettles tea, and I buy fish emulsion.
Pruning and Training
- All pruning cuts should be made just above some part that will continue to grow—a leaf with a dormant bud or a dormant bud on a stem. Cutting too high above will cause that part of the plant to die out and offers an entry point for disease to enter.
- It is also important that cuts heal quickly, so use sharp clean tools for cutting.
- Pinching back: Do it while plants are still young. Use your thumb and forefinger to nip off the tender growing tip at the stem just above the next set of leaves. Once you do this, the plant is forced to put out side shoots, resulting in a bushy compact plant.
- Cutting back: Perennials, especially the woody ones such as sages, lavenders, and thymes, need to be cut back for best blooms the following year. Cut back 1/3 to 2/3 their length when the last flowers bloom in summer. Often this will encourage a second growth. Cut back again in late fall unless severe pruning will weaken the plant's winter survival. These you can cut back in the spring as soon as you see new growth appear. You may need to thin some plants to open up the branches and to clear out old, weak, unproductive growth. Do this when the plant is dormant.