If you’ve just finished repotting your plant in your potting mix, you might be wondering if potting mix is all there is to it. Is there anything else you might be forgetting?
Potting mixes with a balance of water retention, aeration, and nutrition should have everything a plant needs to grow in terms of soil content. Fertilizer is an optional addition during the growing season. Beyond good soil, plants also need adequate sunlight, temperature, and water to thrive.
To help us better understand why this is the case, let’s take a look at what are the requirements for a plant to live.
What does a plant need to grow?
Since we’re on the topic of potting mix, let’s look at what’s going on with plant roots. The roots are where water, oxygen, and nutrients are absorbed into the plant from the soil. All three of those ingredients are essential for a plant to live.
To deliver those three ingredients to the roots, they have to exist in the soil. There are a few qualities that we are looking for in a good potting mix:
- Water Retention – How well the soil holds on to water. A moist soil is needed to deliver nutrients to plant roots in a form that they can absorb.
- Aeration – How light and airy the soil is. Soil with sufficient aeration will provide plenty of small air pockets for plant roots to access oxygen and perform respiration.
- Nutrition – The soil’s nutrient content. The major nutrients are nitrogen (N), phosphorus (P), and potassium (K). These nutrients are needed for a plant’s growth, development, and reproduction.
If your potting mix has good water retention, aeration, and nutrition, your potting mix is enough to grow your plant.
This is all assuming that all your plant’s other requirements are met. Beyond the requirements that come from the soil, plants also need:
- Sunlight – Needed to convert carbon dioxide and water into sugars via photosynthesis
- Optimal Temperature – Plants perform processes like photosynthesis, respiration, and germination at a preferred temperature. If it’s too cold or too hot, those processes will become less efficient, which can cause your plant to struggle.
- Water – Plants need an adequate amount of water to perform photosynthesis and transport nutrients throughout the plant. But not too much, otherwise your plant won’t be able to perform respiration.
- Air – Source of oxygen to perform respiration.
If all of these requirements in addition to the soil requirements are satisfied, your plan should be just fine
When should you use fertilizers?
Fertilizers are an optional addition to your potting mix. Fertilizers are like booster shots for plant nutrition. It’s a way to introduce additional nutrients to the soil to support new growth.
Plants will certainly survive without fertilizers, but their growth will just be a little slower and will produce fewer flowers. Ideally, your plant should be getting enough nutrients from the soil and small amounts from tap water minerals.
Fertilizers should only be added as soon as your plant is entering into the growing season. Even then, it should be applied in moderation (as prescribed in your fertilizer’s instructions) and targeted toward the nutrients your soil is deficient in.
The time of the year for growing season will vary by plant and region (it’s usually around early spring in the US), but it’s the time of year when your plant will do a lot of growing. In order to support this growth, your plant is going to need a solid supply of nutrients.
You don’t want to add fertilizers at the end of the growing season. This can encourage new growth which may not be able to tolerate the incoming cold weather. The unnecessary new growth can cause your plant to waste energy supporting them when they have little chance of surviving the cold.
Does it matter what potting mix you use?
There are many different types of potting mixes that will adequately satisfy your plants’ requirements. The exact ingredients going into the potting mix don’t matter as much as whether or not the mix can provide adequate water retention, aeration, and nutrition.
But the exact type of potting mix you use does matter to some extent because each plant has different requirements and different potting mixes can be intended for different types of plants.
Succulents for example, prefer sandy, very well-draining soil. Most other plants, on the other hand, prefer soil that retains moisture and does not drain moisture too quickly.
While there are generic, general-use potting mix that you can use on most plants, it’s always a little bit more preferable to make your own potting mix custom-tailored to your plant. That way, you can customize the soil mix ratios to fit your specific plants’ needs for optimal results.
It can also be cheaper to make your own potting mix if you are making it in bulk.
How Long is Potting Mix Good for?
Potting mix is usually good for about 6-12 months. It is advisable to replace the potting mix after one or two years so that the nutrient levels, acidity, and microbial content are refreshed.
Over time, potting mix will lose its nutrient content after repeated waterings. You might have heard the term “erosion”. That’s basically what’s happening in your soil: water carries away a little bit of the nutrients every time it drains out of the soil.
There’s also a build-up of anaerobic bacteria in the soil and decaying organic matter which can influence the nutrient levels and acidity of the soil.
In case you want to read more about how that works, you can check out this other article which covers how long potting soil keeps its nutrients.
But before you worry about your soil going bad, it’s worth mentioning that often the need for repotting your plant comes from your plant outgrowing the pot it came in rather than a need to refresh the soil.
You can usually tell your plant needs repotting when you see roots growing out of the drainage holes or the roots are pushing your plant up and out of the planter. If it’s been a long time, you might see the roots form a root ball in the shape of the container.
So to summarize, yes potting mix should be all you need for your plant assuming its other needs are met.
