If you are a space limited urban gardener and want to have a small garden of your own, often your only option is to do patio or balcony gardening. Welcome to the world of container gardening or smart-pot gardening. In addition to selecting the right container for your plant, you also need dirt to grow healthy and robust plants. If you are thinking – what is the big deal about dirt, wait for it. You need good quality living dirt(a soil which has life in it) in proper ratio for the growth of healthy plants. Let’s dive deep into it to discuss about choosing the right potting mix for container garden.
All plants are not made the same. Their nutrition, water and grow medium needed vary quite a bit. Some plants like cactus and succulents need sandy soil. Other plants like tomatoes and most garden vegetables need nutrition rich loose soil with sand and compost and moss in it. Also, there are plants that cannot thrive in clay or wood chips alone. They need some porous medium like sand or perlite.
Why is container soil special?
The soil in your garden or raised beds may do well for the flowers and vegetables in ground. But the same soil may not be suitable for plants when transferred to a container. It all boils down to the quality of the available soil. Container plants grown in balcony or patio completely depends on potting soil for nutrition since the roots cannot sprawl to get enough nutrition from earth. Whereas, in-ground plants can grow deep root system and get nutrients far away from the top to the ground.
Some garden soil is made of clay with less nutrition, this soil when added into the container will not drain well, eventually the plants suffer. For sandy soil the scenario is opposite. The container plants need well aerated and porous soil for drainage. The best soil for plant growth is loamy soil; well aerated soil with organic matter. Choosing right potting mix for container garden is one of the secrets for growing healthy plants.
What is a good potting mix?
Here are a few important things to consider when choosing the right potting mix for container garden. A good potting mix will have proper-
- Aeration: Loose and porous mixture provide good aeration for plants without compacting the soil. Well aerated soil help the plants to absorb maximum nutrition. It also helps in good root growth. In addition to that, well aerated soil helps in better drainage which is important for the plant health.
- Drainage: Proper drainage is essential for the growth of plant. Drainage is must to prevent root rot or any fungal diseases.
- Moisture holding capacity: While we need good drainage, we also need the soil to retain moisture without getting flooded. Since the plants in the potting soil does not go deeper any further than the depth of the container, the soil dries out quickly. Coco coir or peat moss are added along with the potting soil to retain moisture to the desired extent.
- Nutrition: Nutrition is needed for plant growth. The container plant depends on the nutritive value provided by the potting mix as it cannot get soil nutrients like an in-ground plant. Compost made from kitchen scrapes or worm castings or bone meal even sea weed can be added to the potting soil.
Types of soil
Lets discuss about the types of soil. When you go to the garden center to buy soil, there will be different types of soils available for sale. Now you are be confused on what type of soil to pick up for your container plants. Your 10 minute shopping plan has turned to a 30 minutes stop and you are still unable to decide on the type of soil. Here I am going to explain the types of soil and how to select the right soil for container plants.
Topsoil is the natural layer that has formed by the decomposition of organic matter at the surface of the earth over the years. In other words the topsoil is what you have in your garden. The top 5 to 12 inches of the earth surface is typically called the topsoil. It is composed of clay, dirt, sand, and other organic matter. If the top soil is of good quality rich in nutrition and loose soil, it can be used directly in your garden. But does all of us have such top soil in our yard? Most of the time the top soil will be of poor quality with either clay or sand on higher composition with less organic matter. The soil composition is based on local soil, therefore varies from place to place.
It is topsoil but enriched with added compost and organic matter needed for plant growth. The addition of compost will reduce soil compaction and also provide nutrients that will feed the plants. A high quality garden soil is the fruit of hard work. We need patience and time to build up the best soil. The compost needed for the amendment of soil is also expensive when you start from scratch but it will pay off eventually with better results as your garden takes off and the plants thrive well with bumper crops.
Potting mix is the best option to be used for container garden. Sometimes the term Potting soil and potting mix are used interchangeably. The best quality potting soil do not contain soil(dirt) in it. Potting mix is also called soil-less mix. Potting soil is a blend of soil, compost, water retention agent, porosity and drainage increasing agent. The potting mix is made in a way considering air circulation and drainage for roots and water holding capacity for the growth of plants.
Can I use any soil as potting soil?
The short answer is ‘No, but it depends’. Let me explain how.
As we have discussed top soil is generally high in clay or sand. This cannot be added to the container as it does not provide good drainage or moisture retention. Also it contains less nutrition for plant growth. So top soil is ruled out as an option for container plants.
Garden soil is top soil amended with compost, garden soil also called as enriched top soil which is better than topsoil. This soil contain more nutrition but generally lacks in drainage and moisture retention.
This is the reason why plants don’t grow well in pure topsoil or garden soil based potting mixes. The potting mix contains a few additional items which is what makes it an important ingredient in container garden.
What is in a Potting Soil
Now that we know the difference between the top soil, garden soil and potting soil. It is time to see what makes the potting soil special for container plants.
If you observe your store bought potting mix, you will notice white styrofoam like balls or pellets added to it. These are called perlite. They are added to improve aeration of soil. Perlite reduces weight of the soil, increases porosity, water retention and improves aeration in the soil.
Perlite is a volcanic glass. During the heating process the mineral particles pop like popcorn(cool but not for eating) forming white pellets or balls called perlite.
It should be noted that, perlite is a nonrenewable, inorganic, sterile and free of weeds and disease. Therefore when added to potting soil it should be amended with fertilizer.
Store bought potting mixes often contain small mysterious yellow beads. These are nothing but controlled release fertilizer pellets. The balls dissolve in water, thereby releasing the fertilizer gradually to the potting soil. Besides, the yellow beads are different from water beads.
Most of the potting soil will have some sort of compost added to it. The quality and percent of the compost will vary by brand and the specific application of the soil. Organic soils tend to have more compost as they cannot have chemical fertilizers. Whereas the potting mixes which can use fertilizers can get with low quality compost to make up for the bulk.
Sand also has porous properties with good drainage. For clay soil sand works best when combined with compost,worm castings or composted manure will help to improve the quality of the soil. Sand also helps to add bulk to the mix as needed.
Water retention compounds added to the potting soil
In addition to being well draining, the container pots are expected to hold moisture. The risk of heat stroke is much higher in the container plant due to the above ground nature of the root system as well as the inability of the roots to get ground water. So it is important to get water retention without becoming soggy. You can also achieve sufficient water retention by using mulch or coir or peat moss in your garden. Coir or peat moss or perlite are perfect for mixing with the potting soil.
Coco coir is the fiber which is obtained from the husk of coconut. After the edible portion of coconut is used, the shell along with the husk is discarded. The shells are collected for crafts while the husks are decomposed and processed. The coco coir from husks is then compressed into bricks for the ease of packing and shipping. Coco coir is an effective growing media for water retention. Coconut coir is has little to no nutrients in it. Therefore if you are using coco coir as the only or primary plant medium, fertilize it regularly. The coco bricks swell up in size when they are soaked in water for an hour. This expanded coir is then mixed in the potting mix. This will be a great fun project for kids.
Peat moss is the end product of sphagnum moss and other organic materials that decompose in peat bogs over thousands of years. Decompose takes place slowly over the period of time. Peat moss can absorb and retain water very well. Peat moss is also sterile. It doesn’t have any bacteria, fungus, harmful chemicals or undesirable seeds. Peat moss is also sold in pellet form. The nutrition level in peat moss is insignificant. Therefore nutrition in the form of fertilizer or compost should be added. Peat moss is a nonrenewable resource.
As the name suggests, wool Pellets are made from 100 % raw wool. Wool from the belly and underside of the sheep referred as waste wool is not worth as much in market. Hence they are made into pellets to use in garden. Wool pellets hold water very well. Above all, Wool Pellets are all-natural, organic which holds water really well. Also these pellets help to deter slugs. Read further for more information on wool pellets.
Waterbeads are also known as hydrogel or water retention granules. These beads absorb water and retain it to hydrate plants when necessary. When dry water beads are thrown into a mug of water, they expand similar to coco coir. The gels are multipurpose: can be used for decoration, also used as growing media for indoor plants.
Buy or make your potting mix?
It depends on various factors and here is my logic towards making your own.
- If you are using potting soil on a large scale making your own is economical.
- If you grow different varieties of plants like cactus, succulents, ferns, vegetables making your mix is the best option. [The cactus and succulents need more sand than coir or peat moss. On the other hand ferns need more moisture, hence more peat moss should be added]
- Some potting soil has added fertilizer in it. The label will say enough for one growing season(around 6 months), but in my experience the plants didn’t thrive in that soil. You have to amend with extra boost of fertilizer.
Why store bought potting soil is good
- Right mixture for the right plant
- Added water retention alternatives
In commercial scale potting soil mix is sterilized to kill any potentially disease causing micro organisms. Therefore, this soil lacks nutrition needed for the growth of plants. As a result, most of the commercial potting mixes come with added fertilizer(i add more compost to it). If you are making your own potting mix make sure to add some fertilizer to boost up the growth of plants. Potting soils are used only in containers not in raised beds.
Making your Potting mix
I customize the store bought mix to fit the plants I plant. I always keep bags of potting soil, soil with hummus, sand, compost and fertilizer available at my disposal. So I can adjust the composition depending on the needs of the plant.
To make my own general purpose potting mix I usually mix with equal parts of existing potting mix or compost, equal parts of sand with hummus or perlite, equal parts of peat moss or coir with fertilizer. To make specialty mix like succulent mix I reduce the coir and compensate with perlite or sand.
Have a general idea on the quantity of potting mix needed for the container. This is to ensure that you can make enough mix to fill the pots. It all depends on the size of the pot. Always leave an inch of clearance above the potting soil in the container. This prevents any overflow during watering.
Key points to consider when making your potting mix
Your source for potting mix or compost is important. The potting soil sold commercially comes sterilized which is devoid of these pests. If you happen to source your own potting mix, here are few things you should keep in mind:
The fungus Sclerotium causes southern blight which affects a wide array of plants like vegetables, ornamental plants etc. Sometimes sclerotium resembles small yellow balls like fertilizer beads. The fungus overwinters as scleroti in plant debris near the soil surface which also survive in well-drained soil.
Japanese beetle egg
The mature beetles lay their egg in soil about 2 to 3 inches deep in the soil. The eggs are white and oval in shape. In about 2 weeks the eggs hatch and produces the larvae called grubs. Then the larvae undergoes pupae stage before becoming an adult. If you dig around the soil you are more likely to find the larvae or grubs, because they hide well inside the soil. These guys overwinter in the soil. The life cycle is same as monarchs, if only they were beautiful and friendly as monarchs:)
Some people confuse the fertilizer pellet with slug egg. You may find slug or snail eggs in compost or soil. Here is how to differentiate slug eggs from fertilizer pellets. In general, slug eggs are soft, squishy and are found in damp clumps. The pellets are hard and crispy and spread throughout the growing medium.
Can you imagine popping open a slug egg without glove instead of fertilizer bead :). I can’t imagine how many times I have to wash my hands in soap water.
Tip: Always use gloves and may be a safety goggle for protection during experiments.
What to do when you suspect your soil has bug eggs
If you are too curious, scoop some of the soil with eggs in a jar with a loose lid and keep the soil slightly moist. Any bug eggs they may hatch and you will be lucky to have this experience. If nothing happens after two to four weeks its time to discard the soil.
If you hatch out any crawlies in the jar, don’t dump it in garden bed or anywhere you grow edibles or even lawn grass. Who wants those pesky bugs in the garden?
The container garden plants depend on the potting mix for their nutritional and water needs. You need a good quality potting mix for the growth and health of plants. Healthy plants start from good quality(balanced) mix. In reality, the soil for garden is often overlooked.
What are your favorite potting soil tips? Please share us in the comments.