So many new gardeners overlook the importance of soil, but without a good soil mix, your garden plants will produce less and have to work much harder to get the results you want. Indoor and raised gardens especially need a potent soil mix to grow strong plants. Before we dive into the different kinds of soil mixes that work great for indoor and raised gardens, we need to cover a few basics about soil.
It takes time to improve soil. Adding fertilizer doesn’t produce instant results, as the chemicals and nutrients need time to break down and be absorbed by the soil. If you’re planning on having a garden in the summer, you need to start supplementing and strengthening the soil in the fall. Begin saving food scraps from your kitchen, like eggshells, vegetable and fruit matter, and coffee grounds. Grass clippings and dead leaves are also great soil supplements. Take all of these things and either mix them into your garden’s soil or throw them into a bin to start the composting process. Experienced gardeners will tell you that compost and organic fertilizers are the best amendments you can add to your soil.
Bone meal, seaweed, and emulsified fish are great natural fertilizers that are packed with soil-boosting nutrients. Protogrow®  is an excellent source of the natural nutrients found in emulsified fish and seaweed.
Soil and plant roots needs air. Hard, compacted soil doesn’t allow for free air flow, which can result in standing water and root rot. Also, roots have a hard time spreading out and growing larger in compacted soil. Tilling in the spring before planting and then again after adding fertilizer or compost helps loosen the soil and mixes in vital nutrients.
Soil pH is something gardeners also have to monitor. Most plants like a neutral (pH = 7.0) or a slightly acidic soil (pH = 6.5). Test your soil  with a home pH test. If your soil is too acidic (pH below 6.5), add agricultural limestone. If the soil is too alkaline (pH above 7.0), mix in elemental sulfur or sphagnum peat. Changing the pH can take a few months, so don’t expect instant miracles.
Soil Mixes for Raised Gardens
Congratulations – you just made it through Soil 101! On to to the good stuff.
Every year, more and more gardeners build raised gardens for several good reasons. With a raised garden, you control more of the variables by building up the soil yourself with fresh dirt. Raised gardens allow for more airflow, water drainage, and nutrient retention, and they reduce the amount of weeds that try to invade your garden. Raised beds also allow you to bypass existing soil that might old and used up.
Like the name implies, you’ll need plenty of soil to actually “raise” this type of garden. Buying and dumping hundreds of bags of soil, peat moss, and compost really isn’t practical or cost effective, so you should plan on hauling in a few varieties of soils and growing mediums. If you are hauling in dirt, most measurements are in cubic yards:
1 cubic yard = 27 cubic feet
Cubic feet = length x width x height (or depth)
One raised bed gardener recommends an equal mix of top soil, peat moss, coir, and well-rotted horse manure or organic compost. Coir is great for holding and absorbing moisture, as is peat moss. Contact a local farm about horse manure – they usually have more than they can handle!
Mel Bartholomew, creator of the square foot gardening method, recommends a soil mixture of equal parts compost, peat moss, and vermiculite. Another proven mix is equal parts garden soil, peat moss, compost, and vermiculite (or perlite). Vermiculite or perlite helps aerate soil and helps in water retention. Remember: No matter what mixture you use, mix all of the ingredients together. Plants don’t like “layered” soils.
As you can see, compost is key to any soil mixture. You could actually have amazing results just by growing your plants in raised beds made of 100% compost, but that can be expensive.
Indoor Garden Soil Mixes
Indoor gardening is a bit different than raised bed gardening. While you have complete control over nearly every aspect of your gardening, you also have to keep a watchful eye over every change you make.
Because you don’t have sunlight helping your soil in water drainage and evaporation, a good soil mixture that aids in drainage is key. Potting soil is the most common type of soil used in indoor gardening, but if you’re serious about growing some great vegetables, flowers, or herbs, you should consider creating your own indoor garden soil mix. Store bought potting mix might work for a year or so, but after that, the nutrients are depleted and it all begins to decompose, which means you’ll have to transfer your precious homegrown plants to another growing medium, which can add a lot of stress to your plants. Garden soil really isn’t a great option for indoor plants either because it gets dried out and compacted easily.
A self-made indoor garden soil mix will feed your plants for years to come, allowing you to have access to vegetables and herbs year round. Here are a few indoor garden soil mixes that will help you grow the best indoor plants possible:
- On Your Own Potting Soil Mix: Equal parts composted bark, coconut coir, peat moss, perlite , and pumice. Worm casings are also a great supplement to this soil mix. Mix all of these ingredients together to avoid getting a layered soil.
- Garden Soil Mix: Equal parts compost or leaf mold (filtered / screened to remove large material), topsoil from your garden, and coarse sand (either horticultural sand or coarse builder’s sand). With the topsoil from your garden, loosen and break it up as much as possible. Again, mix all of this up before putting it into your indoor garden containers.
- Potting Soil / Compost Mix: Equal parts commercial potting soil, compost, garden soil, and sand.
Any one of these mixes should produce some great results for your indoor garden. As you can see, compost is a big factor in each of these mixes, so don’t downplay it!