One of a gardener’s most joyous events of the new year is sowing those first seeds for a new growing season. Other events occur as indoor gardeners look to re-pot or reinvigorate the soil for their beloved house plants. In other instances, gardeners just need to fill a hole in the yard. All of these different occasions mean that gardeners will probably need to purchase a bag of potting mix.
There seems to be as many different types of potting mix being sold as there are plants in the world. How is one to choose the right mix?
There are some general guidelines one can follow as well as some good old-fashioned shopping sense that will help you. The very first thing you should know is that there are no government standards that regulate these products.
Caveat emptor is the cautionary advice to keep in mind when buying a bag of potting mix.
Know Your Potting Soil Ingredients: Inorganic
Top Soil: This is often sold locally and not bagged by local businesses. Generally speaking you will be getting screened local loam. Many include crushed small stones too. One reliable source recommends that you should find less than 5% of the blend with stones 3 inches in diameter or greater. Because local sources are not bagged for retail sales, you can get a good idea of stone content and soil quality by direct observation.
Many sell packaged products labeled as Top Soil or Garden Soil or something similar. This will be a heavy inorganic product. Hopefully there will be an open package you can see what is in the bag. Top Soil tends to be heavy loam that may have a high clay concentration.
Keep in mind that this product, whether purchased in bulk or bagged, will be suitable for small outdoor projects such as filling holes in the yard or leveling low areas in the lawn. This product can be made suitable for indoor plants with the addition of other potting mix ingredients that will amend the quality of the Top Soil. Top Soil is not recommended for seed starting or to re-pot your treasured house plants.
Perlite: Perlite is a lightweight white puffed up planting media made from certain volcanic rocks. This forms from heating small pieces to a high temperature in an airless environment. Think of Perlite as the popcorn of planting bed media. Super heated stones literally pop up. They have numerous areas to grab and hold moisture as well as plant growing compounds that plants need. There are plenty of interior spaces for both water and fertilizer storage too.
Gardeners use Perlite to aerate heavier garden media such as Top Soil. These lightweight chunks allow air, water and fertilizers to penetrate the soil without clumping. The slight weight will also lower the overall weight of your plant growing media significantly. Perlite will be a noticeable component of most bagged media.
Perlite works for all stages of plant growth from sprouting seedlings to established mature plants. It will loosen hard compact soils in the exterior garden. The light weight and porous nature of Perlite makes it ideal for a wide range of uses.
Mix perlite with other ingredients, unless you are growing hydroponically. Even then, Perlite will not provide the necessary anchorage for large plants.
There are some products that use recycled glass as the material “popped.” These are not true Perlite. These are heavier and often larger too. You can use this recycled glass Perlite instead of normal Perlite – although the product works better as a hydroponic media.
Vermiculite: Heating volcanic material creates vermiculite, as it does Perlite, but vermiculite is slightly different chemically. Vermiculite is also heated to a lower temperature. Vermiculite is light weight, though heavier than Perlite. It is small flat and iridescent in appearance. The “flat” nature of Vermiculite often causes it to layer together if not properly blended with other ingredients.
Vermiculite is also useful for the same reason Perlite is. The light weight sterile nature makes it suitable for seedlings as well as adult plants. It will loosen soils – especially hard, compact garden soils.
Rarely will one ever consider using a potting media solely composed of Vermiculite. It doesn’t hold and grab water and fertilizer quite as well as Perlite. And, because it is a bit heavier, this potting media is not found or used as much as it once was. It works best for starting seedlings and young plants.
Know Your Potting Soil Ingredients: Organic
Peat: This is by far the most common organic component of modern potting mixes. Peat bogs abound in northern countries. The largest producer is Canada. Moss grows on top of, and then compresses, older layers. Over time many of these bogs will eventually become coal when other soil covers and compresses the deep layers. The peat is left to compress in an environment free from oxygen and under pressure.
Peat can grab and hold on to water quite well. In fact, there is a problem with Peat holding too much water. Damage to plant roots can result from the lack of oxygen in this too wet environment. Gardeners should take some care to avoid over-saturating this media.
It’s also important to not let it dry out too much also. Once the Peat becomes too dry it can take some repeated watering to re-hydrate the potting media.
This may sound like Peat is not a good choice to include in a potting media. However, it is lightweight which is quite desirable. It is the number one ingredient found in soil-less potting medias.
There is some small concern that, while it is a renewable product, we may be exploiting the Peat bogs faster than they can replace with new layers of moss. It is not very nutritious as an organic based addition to soil-less mixes. One should maintain a good fertilization program when taking advantage of these mixes.
Coir Fiber: Some commercial products will spell Fiber as Fibre. They mean the same thing.
Coir Fiber is the shredded husk from coconuts. Coconuts are a huge commercial product from many areas of the world especially Sri Lanka, Southern India and all of South East Asia. Sri Lanka exports most of the commercial Coir Fiber.
This product is just gaining in popularity. Like Peat it is renewable. It benefits these Third World countries in that more of a valuable agricultural product can be used for commercial sales. The sale of this waste product is providing a welcome boon to many of these economies.
One reason to begin supporting these soil-less mixes over Peat based mixes is the ability of Coir Fiber to grab and hold onto water. The hollow structure of the fibers permits this feature. In fact, it is quite difficult to over water these media. Coir Fiber will only hold so much water before it allows the excess to run off. This makes it harder to over saturate with water. The second reason is that the fiber will hold fertilizers quite well. The hollow fiber hold fertilizers just like it does water. This prevents the loss and run off to the environment and keeps it close to the plant until needed. And, in the event it should become too dry, Coir Fiber will re-hydrate quickly and easily.
One problem being corrected is that there can be an issue with the PH from natural salt content of Coir Fiber. There used to be a higher salt concentration in the early use of this as a growing media. Most large vendors wash and balance the Ph so that this is becoming less of a concern. There is some difficulty using Coir Fiber with very new seedlings. However, it is excellent for older established plants. And, it has a longer rate of decay than Peat which makes Coir Fiber planting mixes excellent for indoor plants.
Compost: Everyone seems to recognize this. Compost has become so common that many forget the disagreeable problems one can encounter from improperly prepared products. When organic materials are composted properly, one is left with black gold of exceptional worth to plants. The nutritional value is excellent. Plants can capture and use the nutrients as quickly as they can send roots to collect them. Properly-prepared compost is the best method of amending the most compacted of soils. In fact it is far better to use compost to loosen soils than sand. Sand has a tendency to mix with the heavy clay soils and make cement.
Indoor gardeners should avoid using any blends that include compost in their label or list of ingredients unless it is from a well-known respected soil producer. The problem is that too many rush compost through the cycle of production. Unless the compost achieves temperatures or 160 degrees in the pile, micro organisms as well as macro organisms will not be sterilized. There have been some reports of people developing pneumonia and other health concerns after the use of compost containing potting mixes. These reports are rare. There have definitely been observable links of plant viruses and other plant heath problems being transmitted through improperly prepared compost. By far the greatest concern are pest problems especially fungus gnats. These can be quite a nuisance as well as a huge problem for young seedlings which the larva can damage easily.
Compost is best left for exterior gardens where naturally present predators will control many of the problems one may encounter.
Other Ingredients One May Find
Fertilizer: Time released fertilizers are a tremendous boost to new and experienced gardeners alike. While this is an important bonus to find in your potting mix, don’t base your choice on this inclusion. Fertilizers are not that expensive. It is nice in that there is a proper amount for the time advertised on the label. The user does not determine the specific fertilizer component concentration levels. Most commercial blends with time release fertilizers have a balanced blend of the macro nutrients so that most garden needs are met.
Mycorrhizae: Sometimes one will see this listed as Mycorrhizal Inoculant in the ingredient list. There are two types of Mycorrhizae that are important for plant health. It is beyond the scope of this article to discuss the two types found in nature. The product label rarely lists anything beyond the inclusion of these mostly symbiotic fungi.
Yes, Mycorrhizae are a group of microscopic fungi. They evolved along with plants as plants moved from a totally water environment to land hundreds of millions of years ago.
Mycorrhizae surround and sometimes penetrate the cell walls of roots. The relationship between plants and these fungi is that they supply each other with nutrients and moisture. The Mycorrhizae are able to seek and transport water and raw nutrients to plants far better because their cells are considerably smaller and more numerous. There has been evidence where the cilia will grow and scrape soils grains allowing them to capture specific raw materials as they travel through the soil.
There has been some concern about the benefits of Mycorrhizae to plant growth. The general consensus is that because they supply water and nutrients to the plant better than the plant can by itself; plant health is significantly improved. If a plant is healthier it will grow better. Some question quantity and size of fruit. Still, if a plant is happy there will be higher yield than from weak and undernourished plants.
This is a very desirable addition to any potting mix. Always be on the outlook for Mycorrhizae on the label or ingredient list. A healthy plant means a healthy harvest. Simply being healthy means you will have more plants reach adulthood. That alone is a bonus.
Choose for Your Needs
There are so many different blends and manufacturers that it can be a real challenge choosing the right one for your needs. Choosing will become easier once you know the ingredients. Read not only the front label but also the ingredients listed on the reverse.
Most labels will give you a general idea of the intended use. You will see the manufacturer’s name which is a great help. Choose those manufacturers you know or can research easily for recommendations on the Internet. Choose by the name of the product or the label on the front that lets you know the intended use. Internet comments will often describe specific problems others have encountered such as fungus gnats which lets you know that potting mix is not sterile.
Always Keep Notes
It is important to keep notes when you try a new product. There are some you will not like no matter how big the name or reputation of the manufacturer. For example there is one popular mix that contains small bits of charcoal. The idea is that this helps stabilize the soil Ph as well as provide an important source of carbon in the soil. Unfortunately this can be a difficult ingredient for some to use as a potting media especially for young seedlings.
Keep good notes once you find a product you like. Save the packaging or better yet take a picture with your phone so that you have something to stimulate your memory.
Choosing the right retail outlet can also help you with your choice. Believe it or not you will find some of the very best blends at a hydroponic gardening center. The sales people are generally quite knowledgeable too. They will be able to lead you to the most popular blends. The downside is that some of these blends can be a bit more expensive.
Large box stores will have common blends that are proven winners. They often don’t have many with additional supplementary ingredients. The major advantage here is cost, especially during sales for basic easy to use general blends.
Choosing the Right Potting Blend
Choosing the proper blend for your need is often one of the first major challenges for new gardeners. Knowing your ingredients is a must. Researching recommendations on the Internet will help if experienced gardeners are not available to offer their advice. Shop retail outlets other than large box stores for the best soil blends.
Lastly, keep good notes. Sure – you will make some bad choices. You just don’t want to make that choice again. Sometimes the blend itself is not the problem. If you have a tall coffee tree, and you choose a light weight soil-less mix you will find that the tree may like the blend and reward you with good growth yet you will be have to pick the tree up every time there is a small breeze that tips it over. The choice of media in this case did not provide the necessary anchorage weight to counter balance the height of the tree.
Choosing will become easier with each planting season. Even the most experienced will make a bad choice from time to time. Their advantage is experience with the various types of ingredients in blends. Become experienced by purchasing as best you can now, so you can change to something more suitable in the future if you must.