For gardeners wanting to provide optimal nutrition for container-grown plants, John Innes No. 3 compost is a top choice. Developed in England in the 1930s, the John Innes system features science-based compost blends ideal for potting and repotting. The numbers refer to the formula’s nutrient levels, with No. 3 having the highest fertility for mature plants.
Understanding what makes John Innes No. 3 unique along with proper use and care will help you get the most out of this classic potting mix.
What Is John Innes Potting Compost?
All John Innes composts share a common base of loam (soil), peat or peat alternatives, and sand The loam provides nutrients as well as moisture retention. The peat or substitutes improve drainage and aeration. Sand keeps the mix loose
On top of this foundation, fertilizers are added according to plant needs:
- John Innes Seed Compost – Low fertility for starting seeds/cuttings
- John Innes No. 1 – Medium fertility for young seedlings
- John Innes No. 2 – Higher fertility for potting/repotting
- John Innes No. 3 – Highest fertility for mature plants
- John Innes Ericaceous – Acidic mix for ericaceous plants
The nutrient levels are carefully balanced and released steadily over time. This makes John Innes ideal for container growing compared to standard potting soils.
Why Use John Innes No. 3 Compost?
John Innes No. 3 has the highest amount of nutrients to feed mature shrubs, trees, vegetables, and other plants kept in containers long term.
Key Benefits:
- Provides continuous nutrients through one or more growing seasons
- Optimized for plants staying in pots, unlike garden soil
- Excellent moisture retention reduces watering frequency
- Good drainage and aeration prevent compacting
- Ideal pH and nutrient ratios for most plants. Custom blends available for acid lovers.
- Environmentally friendly options use peat alternatives like coir and wood fiber
This premium blend gives plants what they need while their roots are confined in pots. When it’s time to transplant to the garden, the rich John Innes mix helps ease the transition.
How to Use John Innes No. 3 Compost
Follow these guidelines to use John Innes No. 3 effectively:
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Potting – Fill containers 1/3 full with crocks or stones for drainage. Add compost to 1-2 inches below rim.
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Repotting – Water the plant well first. Carefully remove from pot and loosen roots. Place in new pot with compost mix, keeping soil level the same.
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Planting Depth – Set root ball on par with the original soil mark on the stem. Planting too deep can cause rot.
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Firming – Gently firm around roots removing air pockets. But don’t overpack.
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Aftercare – Water well after potting. Shelter transplants until established.
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Feeding – Use a balanced liquid fertilizer every 2-4 weeks during the growing season.
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Summer Crops – When planting summer veggies like tomatoes and peppers, mix in extra compost or organic matter.
Tips for Best Results
Follow these tips to keep John Innes No. 3 performing optimally:
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Store bags of unused compost properly – Keep sealed and out of sun/rain. Open bags will quickly lose nutrients.
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Avoid compressing the mix over time – Repot rootbound plants before the mix gets too dense.
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Adjust pH if needed – Use an acidifier for alkaline soils or lime/wood ash to raise pH.
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Watch moisture levels – Water thoroughly when dry but don’t saturate. Good drainage is key.
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Top dress annually – Scratch 1-2 inches of new compost into the surface of container plants each spring.
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Apply a slow-release granular fertilizer as the John Innes nutrients deplete each season. Or use a liquid plant food every few weeks.
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Repot plants every 2-3 years with fresh John Innes No. 3 to replenish nutrients and provide new growing room.
Common Questions
Is John Innes compost organic?
Traditional John Innes contains mineral fertilizers. But there are organic options available that replace synthetic ingredients with organic matter like worm castings.
Can I make my own John Innes compost?
You can create comparable mixes at home using soil, compost, sand/perlite, and organic fertilizers. But getting the exact John Innes nutrient balance takes trial and error.
How long does John Innes last?
It provides continuous feeding for one growing season. Nutrients diminish over time. Top dress and fertilize in year 2. Repot in fresh mix by year 3.
Can I use John Innes in the garden?
It can be used in garden beds and borders but is formulated specifically for container culture. Mixing with native soil is recommended when transplanting potted plants.
Is John Innes acidic or alkaline?
Standard John Innes is slightly alkaline with a pH around 7.0-7.5. Acid-loving plants need the specialized John Innes Ericaceous mix.
Give Your Plants a Nutrient Boost
Getting the most out of containers requires a top-notch potting mix like John Innes No. 3. This time-tested compost blend provides the steady fertilization that plants need when their roots are confined in pots. With the right care and handling, John Innes No. 3 will keep mature plants thriving season after season.
How does John Innes differ from other composts?
John Innes potting compost is much heavier than other kinds because it is mostly loam, which is soil. It also has peat or a peat substitute, sand, and fertilizer. Most loam used in compost is a mix of sand, silt, and clay. It is sterilized to get rid of weed seeds, pests, and diseases.
Loam is good because it keeps giving plants nutrients and water, drains well, and has good structure and air flow. When plants can take in and release water and nutrients well, this is sometimes called having a high level of “buffering.”
For plants that live a long time and are kept in pots for more than one growing season, John Innes compost is perfect. Also, plants that are young and have been grown in loam-based compost often do better when they are planted in the garden.
Are John Innes composts peat free?
Peat is used in the traditional recipe for John Innes composts, but some are now made with materials other than peat.
