Calculator Inputs
Example Data Table
| Scenario | Wind | Task | Plant height | Windbreak | Distance | Porosity | Gust | Expected status |
|---|---|---|---|---|---|---|---|---|
| Morning spray | 12 km/h | Spraying | 0.6 m | 1.8 m | 5 m | 40% | 15% | Often within cutoff |
| Open bed work | 22 km/h | Transplanting | 0.3 m | 0 m | 0 m | — | 20% | Often above cutoff |
| Fence shelter | 28 km/h | Row cover work | 0.4 m | 2.0 m | 3 m | 30% | 25% | Depends on reduction |
Use the calculator to compare your garden layout against these patterns.
Formula Used
- Wind at plant height (open exposure): U(z) = U(ref) × ln(z/z0) ÷ ln(zref/z0)
- Gust allowance: U(gust) = U(z) × (1 + g/100)
- Windbreak reduction factor: k = kmax × [H ÷ (x + H)] × (1 − porosity)
- Sheltered wind: U(sheltered) = U(gust) × (1 − k)
This is a practical garden model for quick comparisons. For complex terrain and tall shelterbelts, local measurements remain the most reliable reference.
How to Use This Calculator
- Enter wind speed and select your preferred unit.
- Choose the task to apply a conservative cutoff.
- Set measurement height, plant height, and roughness.
- Add gust allowance for short spikes and turbulence.
- Enter windbreak height, distance, and porosity if present.
- Calculate and review status, reduction, and recommendation.
- Download CSV or PDF for recordkeeping and comparisons.
Operational cutoffs for common garden work
Wind cutoffs reduce drift, plant damage, and uneven application. Fine droplets and lightweight covers respond to small increases in speed, especially during gusts. This calculator compares sheltered wind at canopy height to a task-based threshold, helping you decide whether to proceed or delay.
Why height matters more than you expect
Forecasts are often reported at a standard reference height, while most work happens close to the canopy. A logarithmic wind profile adjusts the measured wind down to plant height using surface roughness. Taller crops experience higher local speed than seedlings, so the same forecast can produce different outcomes.
Gust allowance as a safety margin
Average wind can look acceptable while brief gusts exceed safe limits. Adding a gust allowance scales the open wind before shelter reduction is applied. For exposed sites, 15–30% is a practical range; higher values may be appropriate near buildings, corners, or uneven ground.
Interpreting windbreak effects
Windbreak height, downwind distance, and porosity jointly control sheltered conditions. Dense barriers reduce wind strongly but can create turbulence immediately behind them, while moderately porous hedges often provide smoother protection. The reduction factor is capped to avoid unrealistic results in small gardens.
Example data for decision making
Example: input wind 18 km/h at 10 m, plant height 0.6 m, roughness 0.03 m, gust 20%, windbreak 1.8 m, distance 6 m, porosity 40%. The tool estimates sheltered canopy wind and shows if spraying remains within cutoff. Save CSV or PDF to compare morning and afternoon conditions across seasons.
FAQs
1) What does “cutoff” mean in this calculator?
It is a conservative wind limit for a selected task. If sheltered canopy wind exceeds the cutoff, the calculator suggests delaying or improving shelter to reduce drift and plant stress.
2) Which wind speed should I enter, average or gust?
Enter the average or sustained value you have. Use the gust allowance field to account for brief spikes, which helps avoid decisions based only on calm averages.
3) How do I choose surface roughness (z0)?
Use higher values for dense vegetation and obstacles, lower values for smoother ground. Typical gardens often fall around 0.02–0.10 m. If unsure, start near 0.03 m.
4) What porosity should I use for hedges or fences?
Moderately porous barriers often work well. Around 30–50% is a practical starting range. Lower porosity increases reduction, but very dense barriers may produce turbulence close behind.
5) Why is plant height included?
Wind at canopy height is what affects leaves, drift, and covers. Taller plants generally see higher wind than seedlings, so using plant height improves realism for garden decisions.
6) Does this replace field observation?
No. It supports planning and comparison. Local terrain, buildings, and thermal effects can change wind quickly. If your site is complex, confirm with a handheld reading near the canopy.
7) How do I use downloads effectively?
Run multiple scenarios, then export CSV or PDF for your records. Comparing results across times and seasons helps you identify safe windows for spraying, row-cover work, and transplanting.