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Tips for Filling Garden Pots with Soil

When making a container garden, you fill pots with soil, stick in the plants, and add more soil. Here are some tricks to container gardening outdoors that’ll help you grow healthy vegetables and ornamentals and save a bit of money, as well.

*Don’t fill your pot with soil from your garden — even if your garden has the very best soil on the planet. Garden soil is too heavy and too “dirty” (you know, replete with weed seeds, bugs and their eggs, bacteria — stuff that you don’t want in your pots), and it may not drain properly in a pot.

Instead, use potting soil (also called potting mix or container mix). Potting soil is well aerated, sterile, lightweight, and made of a good balance of organic material and mineral particles like peat, sand, or perlite. (Potting soil is actually soilless. That is, it doesn’t contain any dirt.)

At your local nursery or garden center, buy a packaged, sterilized, soilless potting mix that’s meant for container growing. If you need a large quantity, many nurseries sell potting soil in bulk. You may want to try different brands over time to see which ones are easiest to wet and which ones have the best moisture-holding capacity and drainage. But don’t have a personal crisis over which brand of potting soil you buy; caring for your vegetables properly after you plant is more important than choosing the perfect potting soil.

Don’t use potting soil to fill the whole pot. If you’re growing plants in large containers, you’ll be shocked at how much potting soil you need to fill each container. However, you don’t have to fill the whole container with soil. Most vegetable roots penetrate only 10 to 12 inches into the soil. Add more than that and you’re simply wasting soil.

A trick to use less soil is to put empty plastic soda and milk bottles in the bottom third of the container, and then throw the soil on top. The container will be lighter and easier to move, you’ll be recycling to help the environment, and you won’t have to buy as much soil.

Avoid using all the same soil each year. Planting in all of the same soil from last year can be bad news for your plants. Soil nutrition is depleted, and the soil likely has unwelcome diseases, fungal spores, and insects in it. Here are a few ways to reuse old potting soil:

Start fresh by replacing the potting soil in your containers each year. Throw the old soil into other parts of your garden.

Use the old soil in the bottom third of your pots and use new soil on top.

Empty out your pots and clean them. Amend the old soil with some new potting mix, and refill the pots.

Tips for Filling Garden Pots with Soil When making a container garden, you fill pots with soil, stick in the plants, and add more soil. Here are some tricks to container gardening outdoors

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