John Innes No 3 compost has been a go-to potting mix for generations of gardeners wanting to provide optimal nutrition for their container-grown plants But what exactly makes this compost so special? In this article, we’ll explore the origins, ingredients, and best uses of John Innes No. 3 to help you get the most out of this classic planting medium.
What is John Innes Potting Compost?
The John Innes system of potting composts was developed in England in the 1930s by scientists at the John Innes Horticultural Institute. The loam-based mixes were specially formulated to meet the nutritional needs of plants grown in containers.
All John Innes composts start with a base of loam (topsoil) peat or peat alternatives, and sand. The loam provides nutrients and moisture retention. Peat improves drainage and aeration. Sand keeps the mix loose and workable.
On top of this foundation, different levels of fertilizers are added based on the plant’s needs:
- John Innes Seed Compost – Lowest fertility for starting seeds and rooting cuttings
- John Innes No. 1 – Medium fertility for young seedlings
- John Innes No. 2 – Higher fertility for potting and repotting plants
- John Innes No. 3 – Highest fertility for mature plants
- John Innes Ericaceous – Acidic mix for lime-hating plants like blueberries
The nutrients are released steadily over time, making John Innes ideal for container culture
Why Use John Innes No. 3?
Of all the John Innes mixes, No. 3 has the highest amount of nutrients to feed mature shrubs, trees, perennials, and other plants that will stay in containers long term.
Here are some key benefits of using John Innes No. 3:
- Provides continuous nutrients for one or more growing seasons
- Optimized for pot culture, unlike plain garden soil
- Excellent moisture retention reduces watering frequency
- Good drainage and aeration prevent compaction
- Ideal pH and nutrient ratios for most plants
- Some mixes use peat alternatives like coir and wood fiber
For plants confined in pots, this premium blend gives them the fertilization they need to thrive. And when it’s time to transplant to the garden, the nutritious John Innes medium helps ease the transition.
How to Use John Innes No. 3
Follow these guidelines to use John Innes No. 3 compost effectively:
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Potting – Fill containers 1/3 with crocks or stones for drainage. Add compost to within 1-2 inches of rim.
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Repotting – Water the plant well first. Carefully remove from pot, loosen roots, and place in new pot with fresh mix. Keep soil at same level as before.
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Planting Depth – Set root ball level with original soil mark on the stem. Planting too deep can cause rot.
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Firming – Gently firm around roots to remove air pockets, but don’t overpack.
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Aftercare – Water well after potting and 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 tomatoes, peppers, etc., mix in extra compost for nutrition.
Tips for Best Results
Here are some tips to keep John Innes No. 3 performing at its best:
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Store unused bags properly. Keep sealed and away from sun/rain. Open bags quickly lose nutrients.
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Avoid compressing the mix over time. Repot rootbound plants before mix gets too dense.
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Adjust pH if needed with acidifier or lime/wood ash.
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Watch moisture levels. Water thoroughly but don’t saturate. Good drainage is vital.
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Top dress annually by scratching 1-2 inches of new compost into the surface each spring.
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Apply slow-release fertilizer as original nutrients deplete. Liquid plant food every few weeks also works.
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Repot plants every 2-3 years with fresh John Innes No. 3 to replenish nutrients and provide new room for roots.
Frequently Asked Questions
Is John Innes organic?
Traditional John Innes contains mineral fertilizers. But there are organic options using worm castings, organic matter, etc. instead of synthetics.
Can I make my own John Innes compost?
You can try mixing soil, compost, sand, and organic fertilizer. But getting the exact balance of nutrients 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 beds and borders but is formulated specifically for containers. Mixing with native soil is recommended when transplanting.
Is John Innes acidic or alkaline?
Standard John Innes is slightly alkaline, around pH 7.0-7.5. Acid lovers need the special John Innes Ericaceous mix.
Give Your Plants a Nutrition Boost
If you want to get the most out of growing plants in containers, John Innes No. 3 is a great option. This time-tested compost blend provides steady, slow-release nutrition tailored to the needs of mature potted plants. With proper care and handling, John Innes No. 3 will keep shrubs, trees, and other container plantings thriving season after season.
How does John Innes differ from other composts?
John Innes composts weigh much more than other types of potting compost as the key ingredient is loam, or soil, along with peat or peat substitute, sand, and fertilizer. Loam used in compost is usually made of a mix of sand, silt, and clay, and is sterilised to kill weed seeds, pests, and diseases.
The advantage of loam is that it provides a steady supply of nutrients and water, is free draining, with good structure and aeration. This good absorption and release of water and nutrients is sometimes referred to as having a high level of “buffering”.
These qualities make John Innes composts ideal for long-lived plants kept in containers for more than one growing season. Also, young plants growing in loam-based compost often adapt more readily to garden conditions, when planted into the ground.
Are John Innes composts peat free?[image id=”150377″ size=”landscape_thumbnail” align=”none”] Using peat-free John Innes compost to fill a pot
The traditional recipe for John Innes composts uses peat, although there are now some that are made using peat substitutes.