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Watermelon

Citrullus lanatus · cucurbits

At a glance

Light
Full sun
Frost
Very tender
Spacing
1.2 m4 ft (estimate)
Days to maturity
80–100 (estimate)
On this page
Whole striped watermelons
Photo: MmaBaggio · CC0, via Wikimedia Commons.

When do I plant this? › Plan this in your garden ›

The numbers

Sowing depth
2.5 cm1 in
Spacing in row
1.2 m4 ft (estimate)
Mature height
30 cm12 in (estimate)
Mature spread
2–4 m7–13 ft (estimate)
Soil pH (in water)
5.5–6.8 (estimate)
Days to maturity
80–100 (estimate)
Light
Full sun
Feeding
Heavy feeder
Root depth
Medium
Frost tolerance
Very tender
Lifespan
Annual
Habit
Vine
Value to pollinators
Moderate

USDA PLANTS profile

Numbers we’re less sure of

Many of our estimates come from an extension page we’ve read that gets close without pinning the number down. Others are still our own best guess, and on some the sources disagree. Treat them all as a starting point.

Rules that apply to watermelon

Do not plant cucurbits in ground that held cucurbits within 2-3 years. Promising

Do not plant cucurbits in ground that held cucurbits within 2-3 years.

Promising

If you skip this, you lose real yield. The planner warns you.

How it works: Melittia cucurbitae overwinters as a pupa in the soil where its host grew and emerges the next summer; Anasa tristis overwinters as an adult in sheltered sites (plant debris, under boards or rocks) and flies to cucurbits in spring. A host-free break cuts local carryover, but both are strong fliers that re-invade from a distance, so rotation is only partial and works best paired with fall sanitation (destroy spent vines).

Evidence: checked against 4 sources in the research-based literature.

The 4 sources

extension.umn.edu

Squash vine borers UMN Extension
… squash vine borers spend the winter in the soil near their host plants ... Practice rotation ... planting cucurbits in different areas of your garden if possible, or alternate seasons

ohioline.osu.edu

Squash Vine Borer Ohioline (Ohio State Univ.)
Crop rotation away from previously infested fields helps reduce local populations, as overwintering pupae remain in the soil. However ... fields often need to be rotated more than 5 miles away as SVB can fly into fields from long distances.

extension.umn.edu

Squash bugs UMN Extension
Squash bugs can live through the winter as adults in sheltered places, such as under plant debris, around buildings, or under rocks. When adults come out in the spring, they fly to growing cucurbit plants.

vegetables.cornell.edu

Do Rotations Matter within Disease Management Programs? Cornell Vegetables
… 2+ years; avoid other cucurbits
Remedy

Plant cucurbits in different ground, or wait 3 years. Destroy the spent vines in autumn and clear debris and boards nearby. The pupae overwinter in the soil where the crop grew, the adults in the shelter around it. Rotation is only partial; both pests fly in from a distance.

Read the full rule › · open in the planner ›

Don't sow or set out tender crops before your last frost date Well established

Don't sow or set out tender crops before your last frost date

Well established

If you skip this, the planting fails. The planner won’t allow it.

How it works: Ice nucleation in leaf tissue.

Evidence: checked against 2 sources in the research-based literature.

The 2 sources

extension.colostate.edu

Vegetable Planting Guide Colorado State Univ. Extension, GardenNotes #720
From seed: around the date of the average last spring frost

extension.umn.edu

Growing tomatillos and ground cherries Univ. of Minnesota Extension
Transplant to the garden after all danger of frost has passed and the soil has warmed.
Remedy

Sow or set out after the last frost date, or start indoors and transplant once it has passed.

Read the full rule › · open in the planner ›

Don't plant a crop that can't mature before your frost-free season ends Well established

Don't plant a crop that can't mature before your frost-free season ends

Well established

If you skip this, the planting fails. The planner won’t allow it.

How it works: The season's accumulated growing degree days (a running total of its warmth) against the total the crop needs to mature, or the crop's days to maturity against the number of frost-free days.

Evidence: checked against 3 sources in the research-based literature.

The 3 sources

montana.edu

Selecting and Growing Cold-hardy Vegetables in Montana MSU Extension, LILA Fall 2023
Once you know the average dates of the last frost in spring and the first frost in fall, count the number of days between. If the “days to maturity” figure for a desired vegetable is a larger number of days and the “frost tolerance” column indicates “none,” the sad truth is that particular vegetable probably won’t grow to maturity.

planttalk.colostate.edu

Growing Warm Season Vegetables Colorado State Univ. Extension, PlantTalk 1809
Check the seed packet for the number of days until maturity so that there will be enough time for plants to grow before the first killing frost.

extension.colostate.edu

Vegetable Gardening in the Mountains Colorado State Univ. Extension
… high elevation areas don’t accumulate enough “growing degree units” (GDUs, also called growing degree days and heat units) to support some of the most coveted warm season vegetables
Remedy

Start it indoors and transplant it, choose a variety with fewer days to maturity, or skip this crop at this site.

Read the full rule › · open in the planner ›

Blossom-end rot comes from uneven watering, which stops calcium reaching the fruit. It is usually not caused by too little calcium in the soil. Well established

Blossom-end rot comes from uneven watering, which stops calcium reaching the fruit. It is usually not caused by too little calcium in the soil.

Well established

If you skip this, it still grows, just less well. The planner suggests it.

How it works: Calcium reaches the fruit in the water the roots draw up, carried by the xylem along with that stream. When the supply of water is interrupted the supply of calcium is interrupted with it, and the enlarging fruit runs short at its tip, even where soil calcium is adequate.

Evidence: checked against 3 sources in the research-based literature.

The 3 sources

yardandgarden.extension.iastate.edu

Blossom End Rot Iowa State Univ. Extension, Yard & Garden
This is a problem born of calcium deficiency, most often the result of erratic watering.

extension.umd.edu

Blossom End Rot on Vegetables Univ. of Maryland Extension
Mix in 1/4 cup of gypsum (calcium sulfate) with the soil from each planting hole

hgic.clemson.edu

Gardening Myths: Fix Blossom End Rot with Calcium Sprays Clemson HGIC
Calcium is taken up from the soil through the plants

Plus one working note on how the sources were read.

Remedy

Keep the soil evenly moist, without letting it dry out and then soaking it, and mulch to hold that moisture steady. We are not naming a calcium amendment or a rate, because the sources disagree on whether adding calcium helps at all, and any amendment number would need a soil test first.

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Pests of one plant family spread more easily through a solid block of it A good hunch

Pests of one plant family spread more easily through a solid block of it

A good hunch

If you skip this, it still grows, just less well. The planner suggests it.

How it works: Resource concentration. A specialist locates and holds its host more efficiently at higher host density and continuity, so an unbroken run of one family across adjacent beds is an easier target than the same family separated by a non-host (associational resistance).

Evidence: checked against 2 sources in the research-based literature.

The 2 sources

Organization of a plant-arthropod association in simple and diverse habitats: the fauna of collards (Brassica oleracea) Root 1973
… the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments.

Flea beetle movement in a broccoli monoculture and diculture Elmstrom, Andow & Barclay 1988
… strong, direct support for the hypothesis that host plants are harder to find and easier to lose in vegetationally diverse habitats than in monocultures.
Remedy

Where one family fills adjacent beds in a single season, breaking the run with a non-host family between them lengthens the distance the specialist must travel to the next host. The app discloses this and never docks a score. A continuous single-family block can be the right call anyway (a wind-pollinated crop like corn sets better massed), so the app names the trade-off and leaves the choice to the gardener.

Read the full rule › · open in the planner ›

Cold-hardy annuals can be sown or transplanted before the last spring frost (hardy crops about three weeks before, half-hardy about two weeks before). Tender crops wait for the frost itself. Promising

Cold-hardy annuals can be sown or transplanted before the last spring frost (hardy crops about three weeks before, half-hardy about two weeks before). Tender crops wait for the frost itself.

Promising

If you skip this, it still grows, just less well. The planner suggests it.

How it works: Cold hardiness. Hardy crops tolerate hard frost and half-hardy crops tolerate light frost, so they can occupy the ground weeks before frost-tender crops are allowed in. The offset is measured from the last spring frost.

Evidence: checked against 2 sources in the research-based literature.

The 2 sources

extension.illinois.edu

Time Your Vegetable Plantings by Cold Hardiness University of Illinois Extension
… withstand freezing temperatures and hard frosts without injury

extension.colostate.edu

Vegetable Planting Guide Colorado State Univ. Extension, GardenNotes #720
As early as 2-4 weeks before the date of the average last spring frost

Plus 2 working notes on how the sources were read.

Read the full rule › · open in the planner ›

White powdery spots on squash, cucumber, melon or pumpkin leaves are powdery mildew, a fungus that spreads on the wind and strikes the older leaves first. It weakens the plant and the fruit ripens early. Promising

White powdery spots on squash, cucumber, melon or pumpkin leaves are powdery mildew, a fungus that spreads on the wind and strikes the older leaves first. It weakens the plant and the fruit ripens early.

Promising

If you skip this, it still grows, just less well. The planner suggests it.

How it works: The fungus (mainly Podosphaera xanthii) grows on the leaf surface; the spores formed in each spot are carried by the wind to other leaves, and under favorable conditions it spreads until it covers most of the foliage. A plant that loses most of its leaf area to it is weakened, and its fruit ripens prematurely. It takes hold most readily on densely planted vines, plants crowded by weeds, plants in shade and over-fertilized plants.

Evidence: checked against 1 source in the research-based literature.

The source

extension.umn.edu

Powdery mildew of cucurbits UMN Extension
White powdery spots can form on both upper and lower leaf surfaces, and quickly expand into large blotches.
Remedy

Grow varieties with complete or partial resistance, and give the vines air. Space them properly at planting, stake where you can, and keep weeds down. Where powdery mildew has cost a crop before and the variety is susceptible, a fungicide may be needed. Start at the first spots.

Read the full rule › · open in the planner ›

Very tender crops go out about two weeks after the average last spring frost: tomato, pepper, eggplant, lima beans, melons, watermelon, pumpkin and winter squash. Tender crops go in at the frost itself. Promising

Very tender crops go out about two weeks after the average last spring frost: tomato, pepper, eggplant, lima beans, melons, watermelon, pumpkin and winter squash. Tender crops go in at the frost itself.

Promising

If you skip this, it still grows, just less well. The planner suggests it.

How it works: Chilling. A very tender crop is hurt by cool weather as well as by frost: it needs daytime temperatures above 60 °F, and a week of days below 55 °F can stunt it. Setting it out about two weeks after the average last frost gives the days time to warm.

Evidence: checked against 2 sources in the research-based literature.

The 2 sources

extension.colostate.edu

Vegetable Planting Guide Colorado State Univ. Extension, GardenNotes #720
Typically 2+ weeks after the average last spring frost date

extension.illinois.edu

Time Your Vegetable Plantings by Cold Hardiness University of Illinois Extension
Warm-loving vegetables are intolerant of frost and cold and are typically planted between May 10 and June 1.

Read the full rule › · open in the planner ›

Frost can form on a night the forecast low is a few degrees above freezing. Promising

Frost can form on a night the forecast low is a few degrees above freezing.

Promising

If you skip this, the planting fails. The planner warns you.

How it works: On a clear, still night leaves lose heat to the open sky, so a leaf can fall to freezing and ice can form in it while the thermometer, a couple of meters up, still reads a few degrees above.

Evidence: checked against 7 sources in the research-based literature.

The 7 sources

www.weather.gov

Frost and Freeze Information NWS Tallahassee
Issued up to 24 hours when temperature is forecast to be between 32° and 36° on nights with calm winds

www.weather.gov

Freeze Watches and Warnings National Weather Service
… temperatures below 28°F for an extended period of time can kill most types of commercial crops and residential plants.

ipm.ucanr.edu

Freezing and Frost UC Statewide IPM Program
Frost occurs when air is warmer than 32°F but plant tissues drop to 32°F or below because plants radiate (lose) heat into the atmosphere, especially during cool, clear nights.

yardandgarden.extension.iastate.edu

Fall Planting of Vegetables Iowa State University Yard and Garden, Aaron Steil and Kim Hilgers
Tender crops will be damaged or destroyed by a light frost

extension.sdstate.edu

Fall Frost Tolerance of Common Vegetables SDSU Extension, Rhoda Burrows
Crops from more-temperate regions can withstand light freezes (28 to 32 degrees Fahrenheit):

extension.umn.edu

A Minnesota guide to garden timing UMN Extension, Robin Trott
A light frost (32°F) can damage tender plants, while a hard frost (28°F or colder) will kill most warm-season crops.

extension.colostate.edu

Frost Protection and Extending the Growing Season CSU Extension GardenNotes #722, Whiting, O'Meara and Wilson
Radiation frosts occur on calm clear nights that lack cloud cover to hold in heat.
Remedy

The evening before, cover the crops at risk with a sheet or frost cloth, never plastic, reaching the ground and loose at the bottom so the soil's warmth can rise under it, and take it off in the morning. A cover helps least in a long, hard freeze.

Read the full rule › · open in the planner ›

Where frost is rare, sow so the crop grows through months that suit it. A good hunch

Where frost is rare, sow so the crop grows through months that suit it.

A good hunch

If you skip this, you lose real yield. The planner suggests it.

How it works: A crop grows and makes its harvest within a band of warmth: in months colder than its band it grows too slowly to finish, and in months hotter than it a cool-season crop bolts and turns bitter while a warm-season crop drops its flowers.

Evidence: checked against 9 sources in the research-based literature.

The 9 sources

oc4h.ucanr.edu

Vegetable Characteristics UC Cooperative Extension Placer/Nevada Counties, publication 31-043C
Optimum Temperatures for Different Vegetables

www.ucanr.edu

Hold the Tomatoes! UC Master Gardeners of Monterey, San Benito and Santa Cruz Counties, Jazmin Lopez
Average monthly temperatures for cool-season crops during their growing period: 60-65F. This includes, carrots, parsnips, spinach, lettuce, broccoli, and garlic to name a few.

www.fao.org

Technical manual on small-scale processing of fruits and vegetables FAO
Group D: These vegetables thrive in areas where the mean monthly temperatures range between 15 and 18°C. They are intolerant to temperatures between 21 and 24°C, and tolerate weak frosts. This group includes spinach, lettuce, broccoli, beetroot, Brussels sprout, cabbage, radish, rhubarb and watercress.

content.ces.ncsu.edu

16. Vegetable Gardening NC State Extension, Extension Gardener Handbook
Summer. As temperatures rise, cool-season crops bolt and become bitter.

extension.umd.edu

Poor Blossom and Fruit Set of Vegetables University of Maryland Extension
Night temperatures below 60° F. and above 75° F. or day temperatures above 95° F. can cause pepper flowers and small fruits to drop.

daf.nt.gov

Lettuce Northern Territory Government, Agnote B1
In the Top End climate lettuce plantings are restricted to the cooler months from April till July. Hot weather makes the plants to bolt, as they do not form a head but flower instead.

daf.nt.gov

Cabbages Northern Territory Government, Agnote B3
Cabbages are a cool climate crop and their planting in the Top End is restricted from the end of March through to July.

daf.nt.gov

Onions Northern Territory Government, Agnote B9
Onions can be grown only in the cooler months in the Top End, which limits planting from the end of March to the end of May.

edis.ifas.ufl.edu

Florida Vegetable Gardening Guide UF/IFAS EDIS SP103/VH021, Park-Brown, Saracino, Williams and Treadwell
Leaf types grow well in Florida; grow crisphead type only in coolest months.
Remedy

Sow in the months the app names. Outside them, grow a crop whose months they are, or a variety bred for the heat or the cool.

Read the full rule › · open in the planner ›

Where frost sets the season, a crop still needs enough warm months to reach harvest. A good hunch

Where frost sets the season, a crop still needs enough warm months to reach harvest.

A good hunch

If you skip this, you lose real yield. The planner suggests it.

How it works: A crop grows at the pace its days to maturity assume only in months at least as warm as the low end of its band, and in cooler months it grows too slowly to finish, so a frost-free season of cool months can end before the crop is ready.

Evidence: not yet confirmed. It is cited to 8 sources, which a person has yet to read.

What this rests on - 8 pointers

oc4h.ucanr.edu

Vegetable Characteristics UC Cooperative Extension Placer/Nevada Counties, publication 31-043C
Optimum Temperatures for Different Vegetables

www.ucanr.edu

Hold the Tomatoes! UC Master Gardeners of Monterey, San Benito and Santa Cruz Counties, Jazmin Lopez
Average monthly temperatures for warm season crops during their growing period: 65-80F. This includes melons, corn, eggplant, peppers, squash, and tomatoes.

extension.colostate.edu Not yet read by a person

Vegetable Gardening in the Mountains Colorado State University Extension
Of the warm season vegetables, bush beans and summer squash are the most likely to succeed.

extension.umn.edu Not yet read by a person

Growing eggplant in home gardens University of Minnesota Extension
Eggplant needs warm conditions, and will not thrive during a cool season. There are varieties available that thrive in Minnesota’s short summer season.

extension.umn.edu Not yet read by a person

Growing peppers University of Minnesota Extension
In general, smaller-fruited peppers are more tolerant of both cool and hot temperatures

extension.oregonstate.edu Not yet read by a person

Growing vegetables in the Pacific Northwest coastal region Oregon State University Extension, EM 9695
Cold rain, wind, and cool nights can keep coastal soils cold well into summer.

extension.oregonstate.edu Not yet read by a person

Coastal gardening: How to succeed in wind and microclimates Oregon State University Extension
There are some things you can’t do very well on the coast, like tomatoes,

solutions.tennessee.edu

Fall Vegetable Gardens University of Tennessee Agricultural Extension Service, SP291G
Most seed packets and variety descriptions in catalogs estimate the days from planting to maturity. Add about 10 days to this estimate because of the cooler, shorter days in the fall.

Plus one working note on how the sources were read.

Remedy

Grow it under cover, in a greenhouse, tunnel or cloche; start it early indoors and choose its quickest variety; or grow a crop whose months these are.

Read the full rule › · open in the planner ›

Another 132 rules depend on your own garden, like crop rotation, frost dates, sun, spacing and soil. See them all.

Plant teams that place it

When do I plant watermelon? ›

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Milpa Gardens. “Watermelon (Citrullus lanatus).” https://milpa.garden/plants/citrullus-lanatus/

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