How to Choose the Right Soil for Your Garden
Before I became a gardener, the differences between all soil mixtures eluded me. Whenever I needed to fill a pot, pot, or patch of soil, I would simply pick the most economical bag from the big box store. You know the aisle: stacks of colorful bags with minimal information to help you tell the difference. You may come to understand this information through trial and error, as I did, or you can avoid my mistakes by reading further.
What is soil anyway?
What we call soil is really just dirt: it is a combination of organic matter such as broken leaves, twigs, twigs and anything else that has rotted in the space, as well as organisms within the soil itself. Typically the soil contains clay and/or sand, as well as rock particles. The best soil for plants should contain nutrients , enough space for plants to spread their roots easily, and moisture, but not too much moisture. These nutrients must be bound together, otherwise plants will have a hard time getting them. If your soil is too compacted with clay, the roots will not grow well and the plant may be stunted in growth. If there is too much sand, the soil will not hold enough moisture and nutrients. Conditions in a pot or planter are very different from those in a raised bed or just rows of soil.
The topsoil (what you have in your yard) is probably not very good.
When I started gardening, I dreamed of just digging in the yard and planting things. I had romantic ideas about sticking a spade into the garden and finding loamy soil with happy worms. It’s more likely that your yard has poor soil, both due to the nature of the local dirt (perhaps too sandy or clayey) and a lack of nutrients over the years. Either way, dirt from your yard is considered topsoil, and generally speaking, topsoil is not good soil. It contains a lot of unbroken substances, such as leaves and branches, so it can become waterlogged. Unless the soil has been covered for years with leaves that have been mulched in place, it likely won’t have much organic matter to provide it with nutrients or good soil consistency. The topsoil serves primarily as mass, an easy way to fill space during construction. In most cases, you will have to supplement it with nutrients and other substances.
Find mixes for your beds at your local rock yard.
If you are building a brand new garden, you may want to consider using a garden bed mix that you can buy at a big box store. However, this is not the most economical option. Bags are sold by the cubic foot, so you have to think in cubic yards. Most local rock yards have a three- or four-part mix, meaning it includes topsoil, compost, sand and other organic materials. You can have it delivered, which means you simply move it—most likely in a wheelbarrow—from the pile where it’s delivered to your beds.
In most cities, you can buy expensive garden bed mixes that are organic and considered higher quality. My personal opinion is that they are not worth it. I’ve never gotten better results from high quality mixes. The soil you put into your garden is never the end result – you will make changes to it every year, many times a year. This supply is simply a framework to get you started.
Compost is not soil
As you garden, you’ll constantly hear about how important nutrients are to your soil, as well as references to compost as a way to obtain some of those nutrients. You might ask: Since it looks like soil, why not just build an entire bed out of compost? The answer lies in understanding what compost is. When organic matter decomposes, be it leaves, wood, plants, kitchen scraps, animals and their waste, or compostable trash, it turns into a nutrient-rich substance much like soil. Although it is rich in nutrients, it is poor in structure – it is so loamy and full of humus that it needs sand, clay and well. Therefore, usually the soil is fed with compost once or twice a year. You simply add compost on top of the beds and the nutrients are released into the soil through watering and rain. Since you still lose volume in your beds from season to season—due to erosion, compaction, and soil on the plants you pull—this compost helps replenish that volume.
In many cities, compost can be obtained cheaply or even free. The city picks up the collected leaves or collected green bins and makes the resulting compost available to residents. You should ask your city if they have such a program. This is the compost I use exclusively.
Seedlings need planting mixture
There are different soil mixtures for different types of plants, from orchids to cacti. For the most part, they take into account different moisture levels and usually add some slow-release fertilizer. Most flower pots have holes in them or are made from under-fired terracotta, which allows moisture to leach out. To counteract this, potting mixes include vermiculite, perlite, coir or peat moss and other organic materials designed to retain moisture. (By the way, you should try to avoid using peat, a dwindling natural resource, in favor of coco coir.) You may also notice colored granules in the mixture – likely a slow-release fertilizer that will feed the plant over time. Because potting mix does not last forever, the potting mix must be refreshed annually by mixing it again to break up compaction and adding a fertilizer such as Osmocote.
Seed starting mixture is like a baby blanket.
When you start seeds, you need certain conditions. The soil must be very loose and airy for the roots to thrive. The soil should also be fine-grained so that it fills the cells of the seed tray. Tender little seeds and seedlings can be burned by fertilizers, so the seed starting mixture usually lacks any additional nutrients. While you may have success using potting mix instead, seed starting mix does provide optimal success and is always purchased in bags.
Choose the right soil to start with
There is no more important variable in gardening than healthy soil: soil that drains well, has essential nutrients, and can hold the right amount of moisture. Ideally there will be no weeds or pests affecting your plants such as slugs and snails. Believe it or not, much of this is under your control.