When to plant watermelons in Riverside: 2 April – 9 September

In Riverside, watermelon: sow for seedlings from 12 February to 12 August; plant into a greenhouse from 12 March to 9 September; plant out into open ground from 2 April to 9 September.

Watermelon in Riverside: soil, season and weather

In Riverside the soil, not frost, sets the date: the last frost is over around 12 January, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 2 April, 80 days later.

Last spring frost	12 January
Top 7 cm of soil at 18 °C	2 April, 80 days after the last frost
Into an unheated greenhouse	12 March – 9 September; March outside: 9 °C at night, 21.5 °C by day; card 18–35 °C
First autumn frost	19 December, 261 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	31 May – 7 November
Days left for picking	202
Daylight	11:35 on 5 March, 12:34 on 2 April
Watering outdoors when fruiting (card)	every 5 days; the driest month, June, has 0 rainy days

The same dates in Riverside hold for Cucumber, Bell Pepper, Eggplant, Zucchini and Pumpkin.

Watermelon in Riverside: care after planting

Planted on 2 April: in the first weeks water every 5 days.

Feeding, by the card’s schedule from that day:

2 April — feed: balanced (NPK)

Pests and diseases of watermelon to watch for:

Dates count from the first planting day of the window above; a later planting moves them by as many days.

Weather in Riverside during the watermelon season

Days average above the watermelon card's 18–35 °C in July (35.1 °C) and August (35.7 °C). Nights average below 18 °C in April–June and September–December (7.8–17.9 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
April	25.8	11.3	19	3	13:01
May	27.2	13	9	3	13:55
June	31.9	15.4	1	0	14:24
July	35.1	18.1	2	0	14:13
August	35.7	18.9	6	1	13:27
September	33.6	17.9	14	2	12:25
October	29.8	14.6	13	3	11:22
November	24.8	10.5	35	3	10:25
December	20.3	7.8	69	5	9:55

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Riverside, Phoenix is 38 days earlier and Santa Barbara 42 days later.

City	Distance	Date	Difference
Bakersfield	217 km	2 April – 4 September	same day
Santa Barbara	218 km	14 May – 5 September	42 days later
Ensenada	243 km	29 March – 4 September	4 days earlier
Las Vegas	321 km	1 April – 2 September	1 day earlier
Fresno	378 km	10 April – 26 August	8 days later
Phoenix	496 km	23 February – 19 September	38 days earlier

Where to buy watermelon plants and seeds near Riverside

Buy plants ready to set out from 2 April to 9 September (from 12 March to 9 September for an unheated greenhouse); seed for raising your own is sown from 12 February to 12 August. Within 15 km of Riverside OpenStreetMap lists 4 garden centres, 30 plant nurseries, 7 markets and 10 farm shops (collected 28 October 2026).

Saet Byul Asian Market — market
6 km
Super Seafood Market — market
9 km
Corona Family Farm Stand — farm shop
3 km · facebook.com
Gless Ranch Fresh Citrus — farm shop
6 km · glessranch.com

Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.

Questions