The right grafting temperature depends on what you are holding, which crop you are propagating and where the temperature is measured. Cold storage for dormant scions is not the same task as warming a graft union. Use the chart below to identify the task before selecting a protocol.
There is no verified universal apple–pear–peach–citrus optimum or healing countdown on this page. Instead, we distinguish named published examples from the numbers you enter into the calculator.
Grafting temperature reference: which temperature are you measuring?
| Task | Measure | Do not infer | Next step |
|---|---|---|---|
| Dormant scion storage | The temperature beside the bag, including cold spots and day/night changes. | A refrigerator dial is not a tissue-temperature measurement. | Follow the cold, nonfreezing scion-storage protocol. |
| Bench graft holding | Conditions at the union, packing moisture, root condition and bud movement. | One thermostat setting does not establish an optimum for every fruit tree. | Choose a propagation protocol that names your crop and method. |
| Localized hot-callusing | The intended union zone and adjacent material; check whether heat is spreading where it should not. | A seedling mat automatically reproduces a specialized hot-callusing apparatus. | Use the design and limits of the crop-specific system. |
| Outdoor graft aftercare | Actual sun exposure, drying, wrap condition, shoot growth and support. | Warm weather or a calendar date proves the union is mechanically sound. | Inspect without flexing or unwrapping a vulnerable join. |
What published protocols can tell us
Penn State’s bench-grafting guidance is a useful starting point for dormant fruit-tree material and the sequence of preparation. Oregon State’s EM 9075 discusses hazelnut propagation, including specialized hot-callusing. Its crop-specific technique should not be relabelled a universal apple, peach, citrus or walnut protocol.
For a protocol you intend to follow, record its author, crop, method, target measurement location, temperature range, packing conditions and inspection advice. If one of those details is missing, ask before applying heat to valuable material. A citation to a textbook catalog is not verification of a numerical cell in a table.
Two published numbers with different jobs
| Published example | What the number refers to | What it does not establish |
|---|---|---|
| 34–38°F (about 1–3°C) | Mississippi State’s refrigerated storage of dormant scionwood before use. | A heating target for a newly assembled graft. |
| Above 70°F (about 21°C) | Oregon State’s discussion of reliable callusing around a hazelnut graft union. | A universal fruit-tree optimum, upper limit or reason to warm the whole scion. |
Sources: Mississippi State P3402, storage section and OSU EM 9075, hazelnut grafting. OSU describes localized union heating while other parts remain dormant. Use the full crop-specific instructions, not this abbreviated table, to set up propagation equipment.
Check your reading against your protocol
Enter the temperature at the union and the lower and upper targets from your chosen protocol. The calculator converts Fahrenheit to Celsius and flags whether the reading is below, within or above that entered band. The initial band is only an editable example.
Graft Union Temperature Check
Record a union-temperature reading in Fahrenheit and Celsius, and check it against the target band in your propagation protocol.
Enter your details
Enter the target band from your crop-specific protocol. The starting values below are an example, not a universal optimum.
Formula, assumptions, worked example and sources
How this tool works
The comparison subtracts your supplied protocol limits from the measured union temperature. It does not calculate a healing date. Crop, method, moisture, material condition, root activity and bud movement affect the outcome.
Measure at the union with a suitable sensor. The crop selection labels the record; it does not silently select an unverified universal temperature optimum.
Open the full tool, reference notes and questions →
Why there is no “days until healed” result
Visible callus, a sprouting bud and a strong functional union are different observations. A scion can begin growth using stored reserves. Repeatedly disturbing the join to check it may damage it. Keep an observation log and use the crop-specific aftercare guidance rather than a universal timer.
Print an aftercare log or use the heat-mat and thermostat buying checklist. Neither resource replaces electrical product instructions or local horticultural advice.