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Vacation Watering Calculator
Will your plants survive the trip? Size a reservoir, mulch credit and ollas against days away.
Vacation Watering Calculator
Chlorova · updated for 2026
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Click “Calculate” to see your results.
Daily-per-plant figures are warm-season averages; a heat wave, a windy spot or a south-facing balcony can double a thirsty plant's need, while a cool damp week halves it. Treat a zero or negative surplus as a real warning — the tool sizes survival on average weather, and the trip you actually take may not be average.
The vacation watering calculator answers the question that spoils half the pre-trip packing: will the garden survive while you are gone? It weighs what your plants drink each day — scaled down by mulch and shade — against what you can leave them: a reservoir, buried olla pots, a drip timer on the house line. The heart of it is the verdict line: days the supply lasts versus days you are away. A comfortable surplus means pack and go; a shortfall is your signal to add storage, split a zone onto a timer, or finally recruit the neighbor.
How to Use the Vacation Watering Calculator
- Pick the thirstiest crop you cannot afford to lose — it sets the daily draw.
- Enter how many plants you are leaving and the number of days you will be away.
- Add the reservoir litres you can stage — bins, barrels or jugs on a manifold.
- Set the mulch-and-shade saving; a bare hot bed is 0%, a well-mulched one near 40%.
- Count any olla pots or self-watering cones already buried in the beds.
- Read the surplus: days of supply beyond your trip is your whole safety margin.
- If the surplus is thin, add shade and storage or put one zone on a timer.
The Survival-Margin Formula, Explained
Daily need is plants × per-plant litres × the mulch factor, where the factor is one minus the percentage saved. Multiply by days away for the total the trip demands. Your supply is the staged reservoir plus each olla's roughly ten litres of slow seep. The decisive figure is days-of-supply — total supply divided by daily draw — and its margin over your trip length is the verdict: positive and the beds ride out the absence, negative and something browns before you are home.
Why plan around the worst crop: a bed waters to its thirstiest plant, not its average. Six hungry tomatoes sharing a line with a dozen lettuce heads will drink the reservoir dry and leave the greens parched too, so sizing to the dominant crop and then mulching hard is the honest way to build margin. The olla credit is deliberately modest — a buried clay pot meters water by soil tension, sparing a plant or two for days, but it is insurance on top of a reservoir, not a replacement for one.
Worked Example: A Week Away from Twelve Tomatoes
- Twelve tomatoes drink about 2 L each per day in summer heat.
- You laid a thick mulch and a little shade cloth, so enter a 30% saving.
- Daily draw: 12 × 2 × 0.70 = 16.8 L/day.
- For a 7-day trip that is a demand of about 118 L.
- You stage two 30-litre bins (60 L) and bury two ollas (≈ 20 L): 80 L supply.
- Days of supply: 80 ÷ 16.8 = 4.8 — a 2.2-day shortfall, and the verdict is not good.
- Fixes the tool points to: halve the draw with more shade, add a third reservoir, or put one zone on a battery timer.
- Bump to 100 L of supply and days-of-supply clears 7 — now the margin says travel.
Daily Water per Plant
Warm-season per-plant draw that the calculator scales from. Cool, humid or overcast weeks run lower; heat waves and exposed containers run markedly higher, so bias the number up for a balcony.
| Crop | L / plant / day | Notes |
|---|---|---|
| Tomato / cucumber | 1.5–2.5 | Heavy fruit load drinks most |
| Pepper / squash | 1–2 | Peppers wilt dramatically when dry |
| Mixed vegetable bed | 0.8–1.2 | A safe planning average |
| Lettuce / greens | 0.3–0.6 | Shallow roots, quick to bolt dry |
| Established herbs | 0.2–0.4 | The survivors of a short absence |
Key Terms
- Reservoir
- Stored water — bins, barrels or jugs linked to a manifold — that feeds the beds without a hose or tap.
- Olla
- An unglazed clay pot buried and filled; it sweats water into the soil only as roots and dryness pull it.
- Mulch credit
- The percentage of daily draw saved by surface mulch and shade that cuts evaporation.
- Days of supply
- How many days your stored water covers the daily draw — the number the trip length is tested against.
- Surplus
- Days of supply minus days away; the safety margin that decides whether the plan holds.
What This Means Before You Leave
- Water deeply the day you leave, not the morning of: a slow soak banks moisture below the surface, so plants start the trip with a soil reservoir, not just the litres you staged.
- Mulch and shade return more per dollar than any gadget — straw plus a little shade cloth can halve the draw on all but the thirstiest crops, buying days of margin cheaply.
- Group pots by thirst before you stage anything; clustering the hungry tomatoes lets one reservoir and one line serve them, while the herbs at the far end simply ride out the week.
- The gap this tool flags most is balconies and containers, where there is no soil to bank water and a hot afternoon empties a pot in a day — those need a timer, not a jug.
- A battery tap timer running ten minutes at dawn is the most reliable fix when the math comes up short, refilling the daily draw automatically through a hot day the reservoir cannot.
Common Mistakes & Fixes
- Sizing the reservoir for the average plant while the thirstiest crop silently drains it dry and dies first.
- Leaving for a heat-wave forecast with a plan that only just balances, and forgetting the margin is for exactly the days the average does not hold.
- Relying on buried ollas alone for a full week of tomatoes — the seep is gentle but far too slow to carry heavy drinkers unaided.
- Skipping the mulch step, so every litre staged is evaporating from bare soil instead of reaching roots.
- Set-and-forget jugs tipped on their side or manifolds with a pinched line that quietly stop flow days before you get home to notice.
When to Use This (and When Not To)
Use it for any absence longer than a couple of days during the growing season — the window where a missed watering is not recoverable — to decide how much water to stage and whether a timer is warranted. It sizes survivability, not a full irrigation design; for permanent zones use the drip planner, and for daily seasonal depth use the watering-needs tool. A dormant winter garden, a rain-fed outdoor bed, or houseplants that tolerate drought need none of this. And if the surplus is thin, the answer is a neighbor, not a bigger jug.
Vacation Watering Calculator: Frequently Asked Questions
How long can garden plants go without water?
It runs crop by crop and weather by weather. Established herbs and deep-rooted perennials shrug off a week, but fruiting tomatoes in summer heat wilt in two or three days and lettuce bolts in one. That is why the tool sizes the plan off the thirstiest plant rather than the toughest, and adds a bad-weather margin.
Do olla pots really work for vacation watering?
Yes, as partial help. A buried unglazed olla releases water only as the surrounding soil dries, keeping a small root zone steadily moist with almost no evaporation loss. The calculator counts each at a modest ten litres, because no single clay pot can carry a bed of heavy drinkers for long.
Does mulch actually reduce how much I water?
Substantially. A few inches of straw or leaves blocks surface evaporation and cools the soil, so more of each litre reaches roots instead of cooking off. A well-mulched, lightly shaded bed can cut the daily draw by a third to a half, which is exactly the percentage saving this calculator lets you enter before sizing a reservoir.
Should I use a hose timer or a reservoir for a week away?
Judge it by the margin this tool returns. If stored water plus mulch clears your days-away with surplus to spare, a reservoir is simpler and fail-safe. When the math falls short or the forecast is hot, a battery tap timer on a dawn cycle refills the daily draw and is the more reliable choice.
Can I just water heavily right before I leave?
Do it, but treat it as the first step, not the whole plan. A deep soak the day you go banks moisture in the soil and buys a day or two, but it does not stretch a full week for thirsty crops. Feed that head-start in as extra supply or mulch rather than skipping the reservoir entirely.
What if the calculator shows a shortfall?
You have three cheap levers, in order of reliability: add shade and mulch to cut the draw, add reservoir litres to raise supply, or move a stubborn zone onto a tap timer. When all three still leave you short, the honest answer is a neighbor with a key and a watering can.
Sources & Further Reading
- Watering and Maintaining the Home Garden During Absences — University of Minnesota Extension
- Olla Irrigation and Subsurface Watering for Home Growers — New Mexico State University Extension
- Mulch, Evaporation and Irrigation Scheduling in the Garden — Iowa State University Extension and Outreach
Chlorova Gardening Team
Builds, checks and documents every tool we publish
Chlorova editorial review
Checked against extension-service publications
Formula verified against published references · Updated