Fertilising guide
How to fertilise True Service Tree (Sorbus domestica)— schedule & NPK
Also called true service tree, sorb apple.
More about true service tree
About True Service Tree
Sorbus domestica · also called true service tree, sorb apple · edible
The true service tree is a long-lived, rare deciduous tree native to southern and central Europe, with ash-like pinnate leaves, creamy spring flowers and small apple- or pear-shaped 'sorb apples' to 2-3 cm. The fruit is hard and astringent until bletted, when it turns soft, sweet and richly aromatic, traditionally eaten fresh or fermented into perry-like drinks.
Growth habit: Slow-growing, long-lived deciduous tree with an upright then broadly domed crown; can live for centuries and is among the longest-lived Sorbus.
Watch for — Waterlogging intolerance: Roots rot on cold, heavy, wet soils, stunting or killing the tree. Plant only on free-draining ground or improve drainage before planting.
What fertiliser true service tree actually wants — and why
True Service Tree feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.
Balanced (even N-P-K) at planting for roots and frame, then switch to a high-potassium ("high-potash") tomato-style feed once the first flowers open — potassium is what sizes and ripens fruit, not nitrogen.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for true service tree: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed true service tree, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For true service tree:
Low feeding needs. A spring compost mulch on poorer soils helps young trees establish; mature trees seldom need feeding. Avoid heavy nitrogen, which encourages fireblight-prone soft growth. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).
The dormant-season rule matters more than the exact interval: skip feeding entirely when true service tree is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for true service tree
Follow the crop-feed label rate for true service tree — these are calibrated for hungry vegetables. Consistency through fruiting matters more than strength; erratic feeding causes problems like blossom-end rot.
Feeding always goes onto already-damp soil, never dry roots — water true service tree first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the true service tree watering schedule.
Signs you are over-feeding true service tree
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for true service tree:
- Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen).
- Lush foliage hiding the crop; soft growth prone to pests and disease.
- Salt crust on the soil and scorched leaf edges in containers.
Signs you are under-feeding true service tree
- Pale, yellowing lower leaves and stunted growth.
- Small fruit, poor set, and a quickly exhausted plant.
- Blossom-end rot and weak cropping from erratic or insufficient feeding.
If the symptoms point at watering, light or roots rather than nutrition, the full true service tree care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
In containers, fertiliser salts build up fast — water true service tree thoroughly so excess drains from the base each time, and flush pots with plain water every few weeks to prevent a damaging salt build-up.
Organic vs synthetic feeds for true service tree
Organic options
Garden compost or well-rotted manure dug in before planting, plus a liquid comfrey or seaweed feed once fruiting starts. UK: comfrey feed or organic Tomorite; US: Espoma Tomato-tone or Neptune's Harvest. Builds soil and feeds in one.
Synthetic / liquid feeds
A balanced feed at planting then a high-potash tomato feed in fruiting — UK: Growmore at planting then Tomorite (Levington) or Phostrogen; US: a balanced 10-10-10 then Miracle-Gro Tomato or a bloom booster.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising true service tree — frequently asked questions
What fertiliser does true service tree need?
Balanced (even N-P-K) at planting for roots and frame, then switch to a high-potassium ("high-potash") tomato-style feed once the first flowers open — potassium is what sizes and ripens fruit, not nitrogen. True Service Tree feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.
How often should I feed true service tree?
Low feeding needs. A spring compost mulch on poorer soils helps young trees establish; mature trees seldom need feeding. Avoid heavy nitrogen, which encourages fireblight-prone soft growth. Low feeding needs. A spring compost mulch on poorer soils helps young trees establish; mature trees seldom need feeding. Avoid heavy nitrogen, which encourages fireblight-prone soft growth. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).
What strength of feed for true service tree?
Follow the crop-feed label rate for true service tree — these are calibrated for hungry vegetables. Consistency through fruiting matters more than strength; erratic feeding causes problems like blossom-end rot.
What does over-feeding true service tree look like?
Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen). Lush foliage hiding the crop; soft growth prone to pests and disease. Salt crust on the soil and scorched leaf edges in containers. Staying on a high-nitrogen feed once true service tree starts flowering is the classic error — you get a huge leafy plant and a disappointing crop. Switch to high-potash the moment flowers appear.
Should I flush the soil of true service tree?
In containers, fertiliser salts build up fast — water true service tree thoroughly so excess drains from the base each time, and flush pots with plain water every few weeks to prevent a damaging salt build-up.
Keep reading
- True Service Tree care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water true service tree — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise tomato
- How to fertilise pepper
- How to fertilise cucumber
- All 5561 fertilising guides in the Growli library