You may be wondering what type of soil or soil mixture is best for seeds, potted plants, vegetables, or for making a garden bed. There are many factors to take into account, such as what you are planting and in what form. Are you planting flowers? Bulbs? A vegetable garden? Or are you planting houseplants in pots? The most commonly used soil for just about any type of plant is universal potting soil. You can start with this soil for just about any application and then, if necessary, you can use additional items in the soil for vitamins, nutrients, and for the exact type of plant.
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What Exactly is Universal Potting Soil?
Potting soil is made specifically for planting seeds, bulbs, or plants in pots rather than in a garden bed. In pots, the soil doesn’t drain as well as it would if the plants were in the ground and this is even with the highly effective drainage holes on the bottom of your pot or container. Potting soil includes items to help it drain better and not cause root rot, which is common in potted plants where you use garden soil.
You will find different materials, such as sand, pumice, perlite, composted bark, and coconut coir in the potting soil to help with drainage and to make certain the roots of your plants don’t rot in soil that is too moist all the time. Keep in mind, this also means that potted plants which remain outdoors will need to be watered more often so they don’t dry out too much either.
Potting soil also contains some micronutrients to help your seeds, bulbs or plant grow and this is usually in the form of calcium and magnesium. The universal potting soil will also have macronutrients added to it, such as potash, phosphate, and nitrogen for healthy growth, nicer fruits, and veggies, and for more vibrant flowers.
Potting soil is also a great item to use because the natural ingredients that are added to it won’t break down quickly. This enables you to re-use your potting soil from one season to another without the need to purchase additional bags.
What is Potting Mix?
Most people use the terms potting soil and potting mix interchangeably. However, there is a difference between the two items. Potting mix has the same mixture of soil and major components as potting soil, but it also has a higher level of the macronutrients and includes animal-based ingredients such as bat guano, fish meal, and earthworm castings. These items give more beneficial nutrients that are great for growing young plants rather than seeds.
Potting mix breaks down much quicker than potting soil, so you can’t reuse the potting mix from one season to another because it won’t have any nutrients left in it. If you are purchasing potting mix, be sure to check the use-by date on the bag first to make sure it is still viable. Another downside to potting mix and most probably the one that makes home gardeners decide on potting soil instead, is that the animal-based products are smelly since they are bat droppings, worm droppings, and ground-up dead fish.
What Are The Nutrient Mix Numbers on The Bag?
You will likely see a set of three numbers on the bags of potting soil. They refer to the nutrient mix that helps your plants grow as fertilizer included in the mix. The three key minerals are nitrogen, phosphorus, and potassium in this distinct order and are referred to as NPK. The closer the NPK amounts are to being balanced, the more likely it is that this particular potting soil will work best. You are looking for numbers such as 5/5/5. Choose only a potting soil that has the NPK numbers on the bag. If a mix only states “fertilizer” instead, it most probably is not a very good choice and has such a small amount of nutrients that it won’t help your plants grow.
What Are the Functions of Potting Soil?
Universal potting soil has three functions to help your plants. It gives your plants air, water, and nutrients. It allows for your plants to have maximum root growth so they are healthy and it supports your plants physically from falling over.
Vegetable or flower gardens in the soil outside allow the roots of the plants to move through the soil to find nutrients. Your potted plants do not have this option because they are in relatively little soil in a pot or container.
The roots of any plant or flower grow in the spaces between the tiny particles of the potting soil. Your plants also benefit from both air and water that travel in the same spaces as the roots. Water carries the nutrients to the roots for good growth and the air that enters the same spaces helps the roots grow and this process supplies your plants with the nutrients in the potting soil.
When you water your plants, the water moves through the spaces and pushes out the air. The excess water then drains away and allows fresh air to keep the roots healthy and strong without suffocating from the lack of air.
What is Potting Soil Density?
Potting soil density refers to how light or heavy the mix is which is determined by the products that are added to the soil. You want a density that is light and fluffy when it is dry but quite a bit denser when you wet it. If it’s too light, the water will run right through it instead of draining slowly and if it’s too heavy and dense when wet, the roots will either mold or rot from excess water not draining away.
When you are choosing a bag of universal potting soil, pick up the bag. It shouldn’t be so heavy that you can barely lift it. If it’s quite heavy, then it most probably has too many fillers in the mixture of sand or mulch and it was likely exposed to moisture. That is why the bag feels heavy and it’s not a good idea for any sun-loving plant to use it.
Your best bet is to go to a store that has the potting mix stored indoors or at least under a roof in an outside garden center. These bags of potting mix will not likely have been rained on or had dew on the bags to make the mix too wet and heavy.
What Are Plant Specific Potting Soils?
Plant-specific potting soils are used for certain plants and they mimic the soil conditions that the particular type of plant grows in best. These are more expensive to buy for cacti, succulents, roses or violets, and orchids. By looking at your potted or container plants inside and outside, you can use universal potting soil with the same results.
We have an entire article on the best soil for carnivorous plants.
If you decide to start seeds for a vegetable or flower garden in a pot or container, you can start them in a seed starting mix which is said to be formulated for seed germination, and the initial growth period right after they sprout. However, if you go this route, you will then need to repot your plants in universal potting soil when they have 3 to 4 sets of true leaves. So this is a more labor-intensive process.
To answer the questions you have about what is the best soil for planting, it is a universal potting mix with nutrients added to promote germination and good growth for all of your potted and container plants, both inside and outside of your home.
For further reading, you may also be interested in the best manure for vegetable gardening.