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Tips on Filling Containers With Garden Soils

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Planting in containers allows you to work your green thumb in small spaces, such as a condo patio or balcony. You can also use containers to dress up and define areas of a larger yard by placing them near the house, seating areas or flower bed islands. Regardless of the size of the container and the type, such as wood or terra cotta, adding the right kind of soil will help keep your plants healthy.

Preparation

Before you add anything to your containers, move them around to various locations until you’re satisfied with their placement; once you add gravel and soil, the containers often become too heavy to move. Adding a layer of gravel to the bottom of the containers helps them drain properly. Your plants need about 12 inches of soil for adequate root systems with a soil-free lip of about an inch at the top of the container. If the container is deeper than 12 inches, placing filler such as empty capped plastic bottles or plastic bags filled with foam packing peanuts in the bottom of the pot can help you use less garden soil in the container. Leave 13 inches free above the filler for the soil.

Soil Necessities

For the container planting to be successful, the soil must allow for proper drainage while retaining enough moisture to feed the root systems. The plants also need air space within the soil, as densely-packed soil can choke a plant’s roots. To meet the needs of growing plants in a container, garden soil must be mixed with other components. While store-bought potting soil often includes fertilizer, making your own potting soil from garden soil requires added compost or a fertilizer that meets the needs of the plants you plan to add to the container. The fertilizer can be added later, such as spraying a water-soluble fertilizer designed for flowers over your flowering plants.

Garden Soil Only

Although it’s tempting to use only soil out of your existing garden to fill your container, it’s usually not the best idea. Garden soil tends to be denser than potting soil, so it doesn’t drain well, and it requires aeration from worms or grubs. It may also contain weed seeds or fungus spores that can grow in your container. While it’s not a good idea to use only garden soil in your containers, you can add a small amount to other components in your container to help the mixture retain moisture and nutrients. Use garden soil that you dig from several inches below the surface to try to find the cleanest soil available, free of weed seeds and harmful mites and insects that reside on the soil surface.

Soil Mixture

Your recipe for potting soil using your garden soil as a base should contain a mineral component, such as perlite, builder’s sand or vermiculite, and an organic one, such as compost or peat moss. A simple soil mix includes equal parts of garden soil, peat moss and sand. Tailoring the mixture to the type of plant in your container means using additional sand and less peat moss for cacti or extra compost for a container vegetable garden, for example. Flowering plants usually require more water than green plants, so a mixture that retains more moisture in the soil — such as one with a little extra garden soil or peat moss — is best for them.

Tips on Filling Containers With Garden Soils. Planting in containers allows you to work your green thumb in small spaces, such as a condo patio or balcony. You can also use containers to dress up and define areas of a larger yard by placing them near the house, seating areas or flower bed islands. Regardless of the …

Soil in Containers Should Be a Good Mix

Garden soil doesn’t offer enough air, water, or nutrients to container-grown plants. Fortunately, it’s easy to amend.

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I work hard to ensure that the soil in my garden is the best I can give my plants, and they reward me with robust health. Yet that same good soil if transferred to a container would cause the plants in it to languish. That’s because garden soil doesn’t offer enough air, water, or nutrients to a plant growing in a container. Potting soils are specifically formulated to overcome these limitations.

Potting soil needs to drain well but still hold moisture

One of the most important things a potting soil needs to do is provide roots access to air by letting water drain away from them. In the ground, the soil is usually deep enough to let excess water drain beyond root zones. In pots, however, water tends to accumulate at the bottom, despite drainage holes. The smaller the pore spaces of the soil in the pot, the higher that water layer will reach. Larger pores, formed by adding mineral aggregates to potting soils, readily admit water into the soil, then carry it through the medium and out the bottom. Then, all those large, empty spaces can fill with air.

Perlite, vermiculite, calcined clay (kitty litter), and sand are the mineral aggregates most commonly used in potting soils. Perlite and vermiculite are lightweight volcanic rocks naturally filled with air. I prefer perlite over the others because it does not decompose with time nor lose its aerating ability if the potting mix is compressed. Vermiculite is a valuable additive because it prevents some nutrients from leaching away, and it even provides a bit of potassium and magnesium.

A potting mix also must have ingredients that help it retain moisture. This is where organic materials—usually peat moss, sphagnum moss, or coir—come in. They cling to some of the water that the aggregates are helping to drain. Organic materials also hold on to nutrients that might otherwise wash away.

In addition to peat moss, vermiculite, and perlite, commercial mixes often contain sawdust or various grades of shredded bark. Lime may be added to help balance the acidity of the peat moss, and a small dose of fertilizer can often make up for the lack of nutrients.

Adding compost or garden soil can be beneficial

Most gardeners make potting soil by combining perlite or vemiculite with peat or sphagnum moss. Two other organic materials that you could add to your potting mix are leaf mold and compost, which offer a wide spectrum of nutrients.

Adding some garden soil to a homemade potting mix contributes bulk while buffering against pH changes and nutrient deficiencies. The reason that garden soil is rarely added to commercial mixes is because of the difficulty in obtaining a steady supply that is consistent in quality and free of toxins such as herbicide residues.

Customize your mix to suit your plants

Soilless potting mixes are relatively free of living organisms, but mixes made with soil or compost are not. Some gardeners talk about “sterilizing” their potting mixes by baking them in the oven to rid the soil of harmful organisms, limiting the hazards of damping-off and other diseases. What I hope they mean is that they “pasteurize” their mixes. Heating homemade potting mixes to sterilizing temperatures wipes out all living things, beneficial and detrimental, leaving a clean slate for possible invasion of pathogens and causing nutritional problems such as ammonia toxicity. Pasteurization, which occurs at lower temperatures, kills only a fraction of the organisms. The best way to pasteurize your soil is to put it in a baking pan with a potato embedded in the soil. Bake it at 350°F for about 45 minutes. When the potato is cooked, the potting mix is ready.

I don’t pasteurize my potting mix. I rely, instead, on healthy container-gardening practices such as timely watering, good air circulation, and adequate light to avoid disease problems. Beneficial microorganisms in compost and garden soil also help fend off pests.

Lee’s recipe for homemade potting soil

I’ve found that making my own potting soil produces better results than commercial mixes and eliminates the need to monitor my containers’ nutrient and pH levels. With plenty of good soil in my backyard, I have no trouble making this traditional potting medium. It features a mixed bag of ingredients, but I figure that plants, like humans, benefit from a varied diet. This mix can support plants for a year or two without additional fertilization.

Mix 2 gallons each of:
* peat moss
* perlite
* compost
* garden soil

with 1/2 cup each of:
* dolomitic limestone
* soybean meal
* greensand
* rock phosphate
* kelp powder

I place a 1/2-inch mesh screen over my garden cart and sift the peat moss, compost, and garden soil to remove any large particles. I then add the remaining ingredients and turn the materials over repeatedly with a shovel, adding water if the mix seems dry. After a few incantations, the stuff is ready to work its magic on everything from my tomato seedlings to my weeping fig.

Make your own soilless mix

Years ago, Cornell University scientists came up with a formula for a soilless potting mix, which forms the basis for many commercial potting mixes on the market today. By following this recipe, you can easily replicate what is sold in bags at the garden center.

Ingredients
* 1 bushel peat moss
* 1 bushel perlite or vermiculite
* 1/2 pound dolomitic limestone
* 1 pound 5-10-5 fertilizer
* 1 1/2 ounces 20% superphosphate fertilizer

Mix the ingredients thoroughly. The mix is initially hard to wet, so moisten it as you stir it. This saves the trouble of doing so each time you remove some for use.

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