If you’ve ever repotted a houseplant and found yourself with half a bag of potting mix left over, you’ve probably wondered whether it’s safe to use in your outdoor pots. The good news is that, in most cases, the answer is yes.
What matters is whether the potting mix suits the needs of the plant and the conditions it’s growing in.
What’s the Difference Between Indoor Potting Mix and Outdoor Potting Mix?
Many popular houseplants want the same basics from a good potting mix:
- Fast drainage
- Plenty of air around the roots
- An open structure that resists compaction
Outdoor composts are often formulated to hold a little more moisture and may contain slow-release fertilisers to support seasonal bedding plants.
Specialist potting mixes further meet the specific needs of individual plants. There are many ingredients we use to nail that balance of soil consistency, nutrient retention, and drainage structure.
As long as the potting mix you are using is meeting the needs of your plant, you can use it outdoors. But there are still a few things worth knowing.
Outdoor Pots Dry Out Faster
Wind, direct sunlight and warmer temperatures can cause pots to dry much more quickly. An airy indoor mix may therefore need watering more frequently when used outdoors, particularly during summer.
Keep an eye on the soil moisture rather than sticking to a strict watering schedule.
That said, one of the biggest causes of container plant failure is waterlogged soil. Outdoor pots can become saturated after prolonged rain, especially during the British winter.
Free-draining indoor potting mixes can be a big benefit outdoors when the weather takes a turn, and Mediterranean plants such as olives, lavender and rosemary especially appreciate the extra drainage.
Nutrients May Need Topping Up
Some indoor potting mixes contain only a modest amount of fertiliser, while others rely on you feeding the plant regularly.
Outdoor flowering plants can be heavy feeders, so if you’re using an indoor mix outside, don’t forget to fertilise during the growing season according to the needs of the plant.
Adding a slow-release fertiliser when planting can help provide a steady supply of nutrients.
Can You Mix Indoor Potting Mix and Outdoor Compost?
High-quality indoor potting mixes are carefully formulated to provide the drainage and aeration that certain houseplants need. Mixing them with ordinary multi-purpose compost will make the resulting blend denser and more moisture-retentive, harming the benefits that make houseplant mix worth getting in the first place.
For this reason, bulking out an indoor potting mix with standard compost isn’t usually recommended if you’re planning to use it for houseplants.
However, if you simply have some leftover houseplant potting mix, there’s no reason not to mix it into general garden compost for use in flower beds, borders, or large outdoor planters. The added coarse materials can help improve soil structure, and also ensure that nothing goes to waste.
Summed Up
Yes, indoor houseplant potting mix is generally suitable for outdoor pots.
Its excellent drainage can be an advantage, especially for plants that dislike sitting in wet soil. You may simply need to water a little more often and keep up with feeding during the growing season.
Rather than letting leftover mix go to waste, using it in outdoor containers is a practical, economical and perfectly sensible way to give your plants a healthy place to grow.
For more help and advice, head over to our guides section.
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