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Container Gardening: The Best Soil for Containers


A person mixes potting soil ingredients preparing to plant container garden

Container gardening is a fantastic way to bring the joy of growing fresh produce to even the smallest spaces. But your success starts from the ground up. Literally.

Your soil selection has everything to do with healthy plants and how much they yield. So, let's get dirty with some pointers on the best soil for gardening containers.

Why Soil Selection is Important

Think of soil as the foundation for container gardening and your plants. Just as a strong house needs a solid base, plants need good soil.

You must establish plant roots because they help feed your plants. Well, the soil feeds those roots. And your soil ingredients must deliver some essentials, namely water, nutrients, and air.

Here's why soil selection matters:

  • Nutrients: Soil provides essential nutrients for plants to grow healthy and strong.
  • Water Management: The suitable soil helps plants soak up water without drowning or drying out.
  • Root Health: Your soil allows roots to breathe and spread quickly, leading to better plant growth.

Can You Use Topsoil in Gardening Containers?

You might think you can grab a shovel load or two of topsoil from your garden bed to use in containers. Don't. Ever.

Topsoil belongs in the garden. Although it works perfectly fine in that garden environment, it's a poor choice for container gardening. This also applied to bagged topsoil.

Here's why you must avoid using it for container gardening:

  1. Compaction: Topsoil is coarse and heavy, often including stones and clay. When used in gardening containers, it compacts. That reduces aeration and drainage, both disastrous for plant health.
  2. Diseases: Natural soil generally houses weeds and other seeds, not to mention disease-causing pathogens. You'll pass those unwanted items onto your containers and plants.
  3. Nutrients: Topsoil likely falls short of nutrients for your plants. It may contain some from decaying matter, but unless you've added more, it falls short of nutrients needed for potted plants.

What is the Best Soil for Container Gardens?

Look for a potting mix designed for containers. A local garden or home center carries numerous brands and types of potting soil. It contains ingredients designed to enhance aeration, drainage, and moisture retention.

Typically, it includes some or all of these critical items:

  • Sphagnum Peat Moss: It helps hold water moisture and improves aeration.
  • Perlite and Vermiculite: They add air space to the soil for better root health. They're also essential for improving drainage in your gardening containers.
  • Compost: It provides organic material for your plants containing essential nutrients.

Companies like EarthBox specializing in container gardening offer suitable soil mixtures. They have planting kits with pre-measured essentials that retain moisture while providing superior plant nutrition. They also provide potting mix recommendations that work well.

What's the Difference Between Potting Soil and Soilless Potting Mix?

Many people view potting soil and potting mix as the same thing. Not true.

Potting soil may or may not contain soil. However, potting mix is always soilless as a growing medium. The advantage is that the potting mix is sterile and safer for plants. It doesn't contain pathogens like fungi that can harm your plants.

Homemade Potting Mix

If you're more adventurous or fussy about potting mixes, you can create homemade potting soil for container gardening. You'll use many of the same ingredients in bagged mixes. The upside is that you can customize those ingredients to achieve the best balance for your plants.

The main ingredients include:

  1. Peat moss for aeration and water holding capacity.
  2. Coarse sand to improve drainage and aeration. Unlike peat moss, sand doesn't hold water.
  3. Perlite to add drainage. It also keeps the soil light and fluffy to hold air. You can also use vermiculite in your mix. However, it can hold water and nutrients but compact if you use the wrong grade.

How to Make Homemade Potting Mix

You can make soil-based or soilless potting mixes.

When creating a soil-based mix, you'll want to purchase sterilized loam soil, eliminating disease, insect, and weed concerns. Again, avoid taking soil directly from your garden beds.

To create the mixture, follow these steps:

  1. Add a gallon of sterilized loam soil to a bucket.
  2. Add a gallon of moistened peat moss to a gallon of coarse sand, perlite, or vermiculite.

Combine the ingredients in the bucket and adjust the mix for a loose, well-drained mixture. You can adjust the mix by adding sand or peat moss to add or subtract from the soil's texture.

Soilless Homemade Potting Mix

You remove sterilized loam soil from the ingredients with a soilless homemade mix. Instead, use two gallons of peat moss with two gallons of perlite or vermiculite. Then, mix them thoroughly.

With either soil mix, you'll also want to add slow-release fertilizer and small amounts of limestone.

Limestone raises the mixture's pH. It comes in two forms: calcitic limestone and dolomitic limestone. The former includes calcium to strengthen the plant's cell walls. The latter adds magnesium and calcium to the soil.

Start by adding two ounces or four tablespoons to your mixture. You can adjust to achieve the desired pH.

Do Different Vegetables Require Different Soils?

Whatever your mix, you'll want to adjust the soil based on what you intend to grow in your container garden. Plants are a lot like Goldilocks! They look for just the right mixture to grow the best.

For example, tomatoes, peppers, and other vegetables prefer slightly acidic soil. You'll want to target between a 6.2 and 6.8 pH. As a point of reference, neutral soil has a pH of 7.0. You can add sulfur to the soil mix for greater acidity.

Tomatoes also prefer well-drained soil that's nutrient-rich. They're heavy feeders, so you must keep them well-fertilized.

On the other hand, herbs prefer a soil pH of around 7.0.

How Deep Should the Soil Be for Gardening Containers?

Soil depth depends on the plant's roots. Here's a general guideline:

  • Small plants need 6-8 inches of soil.
  • Medium-sized plants need 10-12 inches.
  • Large plants like tomatoes need 18 inches or more.

That also means you'll need to find gardening containers handling those depths. EarthBox, for example, offers several selections with varied depths:

  • Original Gardening Boxes: The company's tried-and-true planting boxes are 11 inches deep. That's a perfect depth to house the most popular vegetables.
  • Herb Planting Boxes: At just over seven inches deep, you can plant basil, thyme, oregano, mint, sage, and other herbs in these gardening boxes.
  • Vegetable Planting Boxes: Their 15-plus inches work for root vegetables with more substantial soil requirements. In these gardening containers, you can plant carrots, beets, onions, turnips, and radishes.
  • Tomato Planters: These planting boxes are 11 inches and perfect for tomato plants. Additionally, you can purchase a tomato growing kit that gives you everything you need to grow ripe, juicy tomatoes.

How Long Does Soil Last in Container Gardens?

It depends on the container gardening system you use. If you make a DIY container garden, the shelf-life of potting mixes might be less than you think. For example, unopened bags of potting soil can last six months before their quality diminishes.

Typically, you'd want to replace the soil in DIY gardening containers every year or two. Why? First, peat moss can compact, reducing aeration and water retention. Second, the container's nutrients diminish from plant consumption and drainage.

You can replenish the soil in a DIY container garden by adding 50% fresh potting soil. You can add more organic matter and slow-release fertilizer to bolster the soil's nutrients.

If you instead use a pre-built container gardening system like the EarthBox, the existing potting mix can be re-used for many years, as long as there are no confirmed cases of blight or other plant diseases. The reason for this is that by following their planting instructions and process, the growing media gets better for your plants. This is due to the recommended addition of dolomite every growing season, which allows for better concentration and readily available elements to be taken by the plant.

EarthBox is Your Source for Successful Container Gardening

Tomatoes growing in an EarthBox container gardening system with attached trellis

EarthBox has been a go-to source for container gardening for three decades. Its growing systems let you successfully grow vegetables, fruits, and herbs, even if you don't have a green thumb.

Commercial farmers developed the system and then tested it in labs. So, you'll enjoy maintenance-free container gardening that can double yields versus garden beds. 100% guaranteed.

 

M ↓   Markdown
K
Kate Pinner
0 points
3 years ago

Someone suggested that pouring a cup of bleach over the potting mix or into the reservoir at the end of the growing season might be beneficial. Any thoughts on this?

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Terry Browning
0 points
3 years ago

I have a soil recipe I use in my boxes for tomatoes. This includes, equal parts of peat moss, topsoil and potting mix. Also, I mix blood meal and bone meal with iron, gypsum, plant tone and a 8-8-8 fertilizer. Lastly the dolomite with liquid cal. Thanks for the watering tip.

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Lee Lewis
0 points
3 years ago

Just a warning -- that "cure" for BER using pickling lime almost killed all my earthbox plants last year. The VERY next day they were wilted and sickly. I'm surprised they even bounced back. I followed the directions exactly. Perhaps that recipe is too strong. I was growing Brandy Boy. Finally, it did NOTHING to stop BER, however I did not try to calcium nitrate.

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EarthBox®
0 points
3 years ago

Hello Lee, thank you for your feedback and we're sorry to hear you almost lost your crop. We would love to learn more about the problem you experienced, so we encourage you to please call or email our Consumer Service Team so we can try to understand a bit more about this issue you experienced. We can be reached Mon.-Fri. 8:30a-4:30p ET at 1-800-4GARDEN if you would like to speak with someone in our office. Thank you!

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Marylyn Pirtle
0 points
3 years ago

Too late for us this year. Better Boy, Zebra, and sweet peppers all have BER. Only Sun Golds have been harvested. Better luck next year, now that we know.

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EarthBox®
0 points
3 years ago

Aww...that's too bad, Marylyn. We hope you try again next season and have better success with your tomatoes the second time around!

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Karen Marks
0 points
3 years ago

Hi! Am loving the earth boxes, but my tomatoes have BER. If I put clean egg shells in the water reservoir, would that help?

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EarthBox®
0 points
3 years ago

Hi Karen, if you want to use eggshells in an EarthBox, we recommend that you dehydrate them and then grind them into a fine powder. They can then be added to the soil alongside the dolomite. We do not recommend that eggshells be put into the water reservoir as they do not break down quick enough to supplement the soil in any meaningful way. We offer a calcium nitrate packet that can be added to the water reservoir weekly that does help prevent BER. You can purchase that as part of our Tomato Replant Kit - https://earthbox.com/earthbox-accessories/earthbox-tomato-replant-kit

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Karen Urbani
0 points
3 years ago

Any other ways to treat BER? My two tomatoes have morphed into an octopus of branches covering the patio and I can't possibly dump the earthbox. Also, any alternatives to Pickling Lime? Doubt I can find this during the Pandemic. And should I fertilize with again/regularly since I am growing many more tomatoes than expected?

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Anonymous
0 points
2 years ago

I started adding a liquid concentrate of Calcium/Magnesium (10ml) once a week down the water tube and I only had a few tomatoes with BER from my 6 boxes. I also installed your watering system this past year and had the best harvest I have every had. The constant water paid off.

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Anonymous
0 points
23 months ago

Hi, I’ve planted Armenian cukes for the past two years in my earthboxes, two plants side by side. Numerous flowers appear but never any fruit. They are outside so pollinators have access. We even rent mason and leaf cutter bees every year to help. Any thoughts on how I can get fruit to develop?

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Anonymous
0 points
4 months ago

As a master gardener, I was taught that nightshade crops, particularly tomatoes, need to be rotated and not planted in the same soil year after year. Are you saying that this is not necessary with the Earthbox system, and that the same soil is safe to plant nightshade crops for up to 10 seasons?

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EarthBox®
0 points
4 months ago

That's correct. You should be reusing the soil season after season unless you have a confirmed plant disease like blight.

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Barbara Petzen
0 points
3 years ago

I've heard that dropping a Tums into the watering tube occasionally can also help prevent BER. Would love to know what your advice is on this, and if others have had success with this cheap and easy method?

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gary bachman
0 points
3 years ago

Barbara, you would need to add something like 275 Tums to equal just setting up using the correct amount of dolomite

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Kathy Sieling
0 points
3 years ago

On my better boy tomatoes, looks like one or two small tomatoes are developing blossom end rot, the others are not. Planning n adding calcium to the boxes today, but should I pluck off the small ones that appear to be developing blossom end rot?

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EarthBox®
0 points
3 years ago

Hi Kathy, Any tomatoes that have Blossom End Rot (BER) should be picked and discarded as soon as possible. Picking off the affected tomatoes as soon as possible will allow the plant to put energy into producing more flowers and fruit. Be sure to add 1 teaspoon of Calcium Nitrate to the water reservoir one time each week to help prevent BER.

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Kathy Sieling
0 points
3 years ago

Where do purchase calcium nitrate and all I could find is Bonide Rot Stop.

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EarthBox®
0 points
3 years ago

Your local garden center should have some, or you can also buy it from us by calling 800-442-7336.

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Sharon Babbitt
0 points
3 years ago

I have used the earth box planting mixture.. Bought the refertilizer packs... I followed instructions to a tee.. but my zucchini have big leaves and my zucchini get about 2-3 inches long and rot off... not sure what is happening. Can you tell me what is wrong?

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EarthBox®
0 points
3 years ago

Hello Sharon, thank you for your question. The problem you are describing with your zucchini plant is lack of fertilization. Basically, your female squash flowers (the ones with the tiny zucchini fruits behind the blossom) are not being pollinated. The fruit will only grow so much and then it begins to rot if the flower did not receive pollen from the male flowers (the flowers without the fruit and with just a straight stem behind the blossom). You can pick the male flowers and manually pollinate the females if you do not have any bees, butterflies, or other pollinators in your area, which will allow the tiny fruits to "set" and mature into full-size.

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Anonymous
0 points
19 months ago

Don't you mean "lack of pollination" rather than "lack of fertilization"?

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Laura Fulton
0 points
3 years ago

How do I apply rot stop (Calcium 9.2% solution to earth box container to prevent blossom end rot. My plants are small now. Two in one earth box. Thank you

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EarthBox®
0 points
3 years ago

Hi Laura, Bonide Rot Stop is a foliar spray. Directions on their label state to "apply to the point of run-off onto the foliage and fruit during periods of rapid growth or following excessive rain fall." We advise you apply this in the evenings when temperatures are lower to avoid foliage burn. They do not recommend using this regularly, as it can cause leaves to burn if used more often than every 7 days.

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Anonymous
0 points
8 months ago

I had a bad time with BER a few years back and started adding calcium nitrate once a week. Since then I’ve started adding it before it starts and so far so good. I was reading and noticed that I should reuse the soil every year, I haven’t been doing this but I’m really glad I don’t have to empty the boxes and buy new soil every year 😮. This year I got mixed up and have been adding it to tomatoes and squash, not peppers. Now I have quite a few peppers to remove.. 😐. I’m at the age where I have to learn things over lol Julien Bowles

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