When To Plant Tomatoes In Colorado (& Dates For Different Areas)

chenell
By: Chenell - Lead Writer and Gardening Advocate
Published:

It’s hard to beat the flavor of a sun-ripened tomato from your own garden. But if you plant your tomatoes too early, they won’t survive those unexpected early Spring frosts. So when is the best time to plant tomatoes in Colorado?

Air and soil temperature are the name of the game when it comes to growing tomatoes. For tomatoes to grow properly, the soil temperature should reach at least 55 degrees Fahrenheit, but preferably 60 degrees during the day.

You want to be aware of when the last average spring frost happens in your area – this is also called a Hardiness zone. Hardiness zones are essentially a measure of when your growing season starts and ends based on the local climate in your specific location.

While the season for planting tomatoes typically starts around May, this will vary depending on your hardiness zone. Because CO is a decent-sized state, ranking 8th overall, there are 5 “zones” within it.

indeterminate tomato varieties

When to Plant Tomatoes in Colorado

The best time to plant tomatoes in Colorado is after the last frost has passed, which should be around May.

Here is a breakdown of some of the bigger regions in Colorado and when to start planting tomatoes based on which area you might live in or closest to.

RegionLast Frost DateStart Seeds IndoorsState
LancasterApr 27Mar 16PA
Bucks CountyApr 19Mar 08PA
Central PAMay 10Mar 29PA
Western PAApr 30Mar 19PA
Philadelphia AreaApr 04Feb 21PA
Huntsville/North AlabamaMar 31Feb 17AL
Birmingham/North CentralMar 31Feb 17AL
Tuscaloosa/West CentralMar 25Feb 11AL
Montgomery/East CentralMar 20Feb 06AL
Mobile/Beaches/SouthwestMar 09Jan 26AL
Dothan/SoutheastMar 10Jan 27AL
AnchorageMay 04Mar 23AK
JuneauMay 09Mar 28AK
FairbanksMay 21Apr 09AK
WasillaMay 23Apr 11AK
KetchikanApr 13Mar 02AK
KodiakJun 02Apr 21AK
SitkaMay 09Mar 28AK
FlagstaffJun 10Apr 29AZ
KingmanApr 10Feb 27AZ
Phoenix/Tempe/MesaFeb 24Jan 13AZ
TucsonFeb 06Dec 26AZ
YumaJan 31Dec 20AZ
WinslowApr 29Mar 18AZ
WillcoxApr 16Mar 05AZ
BentonvilleApr 19Mar 08AR
JonesboroApr 07Feb 24AR
HelenaMar 23Feb 09AR
Little Rock/StuttgartApr 01Feb 18AR
ArkadelphiaApr 01Feb 18AR
TexarkanaMar 24Feb 10AR
El DoradoMar 31Feb 17AR
Van BurenApr 03Feb 20AR
Crescent CityMar 25Feb 11CA
AlturasJun 12May 01CA
ReddingFeb 28Jan 17CA
SacramentoFeb 17Jan 06CA
Oakland/San FranciscoJan 23Dec 12CA
Los Angeles/Anaheimn/a#VALUE!CA
San Diego#N/A#N/ACA
NeedlesJan 16Dec 05CA
San BernardinoFeb 10Dec 30CA
Santa BarbaraJan 27Dec 16CA
DenverMay 12Mar 31CO
PuebloMay 04Mar 23CO
Grand JunctionApr 20Mar 09CO
DurangoMay 29Apr 17CO
LamarMay 05Mar 24CO
Steamboat SpringsJun 14May 03CO
DanburyApr 26Mar 15CT
Bridgeport/New HavenApr 09Feb 26CT
HartfordApr 23Mar 12CT
NorwichApr 21Mar 10CT
RockvilleApr 23Mar 12CT
NorwalkApr 23Mar 12CT
DoverApr 09Feb 26DE
WilmingtonApr 13Mar 02DE
NewarkApr 14Mar 03DE
Rehoboth/BeachesApr 02Feb 19DE
Georgetown/SeafordApr 09Feb 26DE
Fort Lauderdale/Miamin/a#VALUE!FL
JacksonvilleFeb 14Jan 03FL
OrlandoJan 30Dec 19FL
Tampa/Clearwater/Ft MyersFeb 09Dec 29FL
St. PetersburgJan 28Dec 17FL
TallahasseeMar 19Feb 05FL
Florida Keysn/a#VALUE!FL
DaltonApr 09Feb 26GA
AtlantaApr 01Feb 18GA
AugustaMar 06Jan 23GA
MaconMar 29Feb 15GA
SavannahMar 12Jan 29GA
BrunswickFeb 22Jan 11GA
AlbanyMar 19Feb 05GA
AthensMar 31Feb 17GA
Hilon/a#VALUE!HI
Honolulun/a#VALUE!HI
Mauin/a#VALUE!HI
Waipahun/a#VALUE!HI
Pearl Cityn/a#VALUE!HI
Kailuan/a#VALUE!HI
BoiseApr 30Mar 19ID
Twin FallsMay 15Apr 03ID
SandpointMay 15Apr 03ID
Challis#N/A#N/AID
DuboisMay 27Apr 15ID
PocatellaMay 25Apr 13ID
SpringfieldApr 20Mar 09IL
ChicagoApr 17Mar 06IL
PeoriaApr 29Mar 18IL
MurphysboroApr 16Mar 05IL
Mount VernonApr 17Mar 06IL
CharlestonApr 22Mar 11IL
EvansvilleApr 02Feb 19IN
BloomingtonApr 22Mar 11IN
IndianapolisApr 27Mar 16IN
Fort WayneMay 03Mar 22IN
South Bend/GoshenApr 30Mar 19IN
Terre HauteApr 22Mar 11IN
ClintonApr 29Mar 18IA
Cedar RapidsMay 03Mar 22IA
Council BluffsApr 23Mar 12IA
Des Moines/NewtonApr 24Mar 13IA
WaterlooMay 02Mar 21IA
WaukonMay 07Mar 26IA
Sioux CityMay 04Mar 23IA
Fort ScottApr 12Mar 01KS
TopekaApr 21Mar 10KS
GoodlandMay 08Mar 27KS
ColbyMay 08Mar 27KS
Ulysses/Garden CityMay 02Mar 21KS
SalinaApr 23Mar 12KS
WichitaApr 16Mar 05KS
IndependenceApr 12Mar 01KS
Lexington/FrankfortApr 20Mar 09KY
LouisvilleApr 20Mar 09KY
PaducahApr 11Feb 28KY
Bowling GreenApr 11Feb 28KY
CorbinApr 22Mar 11KY
Hazard/PikevilleApr 23Mar 12KY
HendersonApr 16Mar 05KY
ManchesterMay 05Mar 24KY
MurrayApr 11Feb 28KY
ShreveportMar 07Jan 24LA
AlexandriaMar 06Jan 23LA
BastropMar 24Feb 10LA
Lake CharlesFeb 26Jan 15LA
Grand Isle/Port SulphurFeb 24Jan 13LA
SlidellMar 05Jan 22LA
New OrleansFeb 23Jan 12LA
Baton Rouge/LafayetteMar 10Jan 27LA
Presque IsleMay 22Apr 10ME
EastportMay 03Mar 22ME
BrunswickMay 06Mar 25ME
GreenvilleMay 13Apr 01ME
BangorMay 09Mar 28ME
AugustaMay 23Apr 11ME
Bar HarborMay 01Mar 20ME
BaltimoreApr 06Feb 23MD
BowieApr 29Mar 18MD
CumberlandApr 22Mar 11MD
FrederickApr 07Feb 24MD
SalisburyApr 09Feb 26MD
AnnapolisMar 31Feb 17MD
HagerstownApr 17Mar 06MD
BarnstableMay 01Mar 20MA
New BedfordMay 05Mar 24MA
SpringfieldMay 09Mar 28MA
BostonApr 08Feb 25MA
GardnerMay 08Mar 27MA
GreenfieldMay 06Mar 25MA
PittsfieldMay 13Apr 01MA
Ann Arbor/DetroitMay 11Mar 30MI
FlintMay 13Apr 01MI
CheboyganMay 18Apr 06MI
MarquetteMay 15Apr 03MI
KalamazooMay 04Mar 23MI
Grand RapidsMay 14Apr 02MI
LansingMay 07Mar 26MI
Saint PaulApr 30Mar 19MN
Hallock/WarrenMay 15Apr 03MN
Grand FallsMay 29Apr 17MN
Grand MaraisMay 27Apr 15MN
MarshallMay 10Mar 29MN
DuluthMay 22Apr 10MN
PlymouthMay 04Mar 23MN
TupeloMar 29Feb 15MS
MeridianMar 23Feb 09MS
JacksonMar 13Jan 30MS
HattiesburgMar 15Feb 01MS
BiloxiFeb 26Jan 15MS
VicksburgMar 05Jan 22MS
GreenvilleMar 21Feb 07MS
Kansas CityApr 13Mar 02MO
KirksvilleApr 28Mar 17MO
Jefferson CityApr 16Mar 05MO
St. LouisApr 12Mar 01MO
Poplar/BluffApr 05Feb 22MO
SpringfieldApr 16Mar 05MO
KalispellJun 07Apr 26MT
GlasgowMay 08Mar 27MT
BillingsMay 15Apr 03MT
BozemanJun 03Apr 22MT
HelenaMay 15Apr 03MT
Yellowstone/Miles Cityyear-round risk#VALUE!MT
LincolnApr 30Mar 19NE
North PlatteMay 08Mar 27NE
NorfolkMay 06Mar 25NE
Chadron/NorthwestMay 21Apr 09NE
McCookMay 07Mar 26NE
ElyJun 19May 08NV
Las VegasFeb 11Dec 31NV
Carson City/RenoMay 14Apr 02NV
ElkoJun 03Apr 22NV
WinnemuccaLoading...Loading...NV
AustinMay 30Apr 18NV
Nashua/Manchester/ConcordMay 03Mar 22NH
KeeneMay 19Apr 07NH
ConwayMay 13Apr 01NH
BerlinMay 20Apr 08NH
Idlewild/ColebrookJun 04Apr 23NH
Toms River/Long BranchApr 30Mar 19NJ
Atlantic CityApr 24Mar 13NJ
TrentonApr 25Mar 14NJ
Edison/Elizabeth/NewarkApr 21Mar 10NJ
VinelandMay 01Mar 20NJ
Sussex/FranklinMay 08Mar 27NJ
FarmingtonMay 08Mar 27NM
GallupMay 17Apr 05NM
Las CrucesMar 20Feb 06NM
AlbuquerqueApr 15Mar 04NM
Santa FeMay 20Apr 08NM
CarlsbadMar 27Feb 13NM
RoswellApr 04Feb 21NM
Lake PlacidJun 01Apr 20NY
WatertownMay 08Mar 27NY
AlbanyMay 02Mar 21NY
New York CityApr 03Feb 20NY
IthacaMay 18Apr 06NY
RochesterApr 30Mar 19NY
BuffaloMay 07Mar 26NY
JamestownMay 15Apr 03NY
SyracuseMay 05Mar 24NY
BooneMay 10Mar 29NC
AshevilleApr 26Mar 15NC
CharlotteApr 06Feb 23NC
Greensboro/Raleigh/Chapel HillApr 03Feb 20NC
Greenville/Elizabeth CityApr 02Feb 19NC
FayettevilleApr 05Feb 22NC
WilmingtonMar 26Feb 12NC
Bismarck/South CentralMay 14Apr 02ND
Bowman/SouthwestMay 21Apr 09ND
Fargo/SoutheastMay 15Apr 03ND
Grand Forks/NortheastMay 16Apr 04ND
Minot/North CentralMay 15Apr 03ND
McClusky/CentralMay 13Apr 01ND
ClevelandApr 14Mar 03OH
AkronMay 06Mar 25OH
ColumbusApr 30Mar 19OH
CincinnatiApr 24Mar 13OH
AthensMay 01Mar 20OH
LimaApr 28Mar 17OH
ToledoApr 27Mar 16OH
Boise CityMay 01Mar 20OK
BeaverApr 28Mar 17OK
Oklahoma City/Shawnee/ChickashaApr 08Feb 25OK
Lawton/AltusApr 07Feb 24OK
TulsaApr 08Feb 25OK
Bartlesville/MiamiApr 19Mar 08OK
PoteauApr 03Feb 20OK
AstoriaApr 03Feb 20OR
PortlandApr 11Feb 28OR
SalemApr 13Mar 02OR
LakeviewJun 12May 01OR
EugeneApr 25Mar 14OR
John Day/Baker CityJun 04Apr 23OR
MedfordApr 18Mar 07OR
PendletonApr 30Mar 19OR
BendJun 14May 03OR
ProvidenceApr 28Mar 17RI
HartfordApr 23Mar 12RI
Stamford/BridgeportApr 18Mar 07RI
Willimantic/RockvilleMay 03Mar 22RI
WoonsocketApr 28Mar 17RI
Charleston AreaFeb 17Jan 06SC
ColumbiaMar 29Feb 15SC
SpartanburgApr 14Mar 03SC
Myrtle BeachMar 20Feb 06SC
FlorenceMar 27Feb 13SC
AberdeenApr 17Mar 06SD
BrookingsMay 11Mar 30SD
Rapid CityMay 09Mar 28SD
Sioux FallsMay 06Mar 25SD
WatertownMay 12Mar 31SD
ChattanoogaMar 31Feb 17TN
KnoxvilleApr 19Mar 08TN
KingsportApr 16Mar 05TN
CookevilleApr 20Mar 09TN
NashvilleApr 10Feb 27TN
MemphisMar 24Feb 10TN
JacksonApr 09Feb 26TN
ArlingtonMar 16Feb 02TX
AustinMar 18Feb 04TX
Corpus ChristiJan 28Dec 17TX
DallasMar 18Feb 04TX
El PasoMar 07Jan 24TX
Fort WorthMar 18Feb 04TX
HoustonFeb 18Jan 07TX
PlanoMar 14Jan 31TX
San AntonioMar 02Jan 19TX
MonticelloMay 24Apr 12UT
MoabApr 18Mar 07UT
Salt Lake City/OgdenApr 07Feb 24UT
Saint GeorgeMar 25Feb 11UT
DuchesneMay 13Apr 01UT
Fillmore/RichfieldMay 08Mar 27UT
Montpelier/BarreMay 12Mar 31VT
NewportMay 20Apr 08VT
GuildhallMay 24Apr 12VT
BurlingtonMay 08Mar 27VT
WoodstockMay 19Apr 07VT
BrattleboroMay 19Apr 07VT
Washington/DCMar 30Feb 16VA
RichmondApr 09Feb 26VA
Norfolk/Suffolk/Virginia BeachMar 30Feb 16VA
DanvilleApr 15Mar 04VA
RoanokeApr 09Feb 26VA
CharlottesvilleApr 07Feb 24VA
BlacksburgMay 01Mar 20VA
Bellingham/Mt. VernonApr 08Feb 25WA
OlympiaMay 05Mar 24WA
Forks/Port AngelesApr 29Mar 18WA
Walla WallaApr 05Feb 22WA
SpokaneMay 01Mar 20WA
WenatcheeApr 10Feb 27WA
Morgantown/ClarksburgMay 02Mar 21WV
MartinsburgApr 23Mar 12WV
CharlestonApr 23Mar 12WV
BeckleyMay 14Apr 02WV
ParkersburgApr 20Mar 09WV
WheelingApr 26Mar 15WV
Milwaukee/KenoshaApr 25Mar 14WI
MadisonMay 07Mar 26WI
Green BayMay 13Apr 01WI
Sheboygan/ManitowocMay 01Mar 20WI
Wausau/Stevens PointMay 12Mar 31WI
Eau ClaireApr 30Mar 19WI
HaywardMay 29Apr 17WI
CheyenneMay 20Apr 08WY
LaramieJun 10Apr 29WY
GilletteMay 21Apr 09WY
Rock SpringsMay 31Apr 19WY
CasperMay 16Apr 04WY
RawlinsJun 07Apr 26WY

Now, of course, these dates are estimates. Some years Mother Nature likes to give us an extra month of spring, and the next year she gives us 3 weeks less.

The Farmer’s Almanac has a great tool for checking these dates getting you down to the zip code level of accuracy. You can also use the chart below to get an estimation.

You can test the ground temperature yourself with a soil thermometer too just to make sure.

When to Start Tomato Seeds Indoors

With most tomato varieties, you can start seeds indoors around 6-8 weeks before the last frost date.

When you sow indoors, you’re giving yourself a head start on the growing season.

But you don’t need to be starting all of your tomato plants at the same time either.

Succession planting can help you make sure you always have fresh tomatoes, even enough for a fall harvest. This is a great idea if you’re growing a lot of determinate tomatoes as well.

Let’s dig deeper here (see what I did there?!). Let’s say you start two tomato plants in April, but then two in May, then you can have a successive harvest and instead of harvesting 100 tomatoes at one time, you can break it up into 50 each harvest.

tomato seedlings

When to Transplant Tomato Seedlings Outside

Whether you’re growing tomatoes from seed or bought some young plants at a garden center, you want to make sure you transplant seedlings outside properly.

Of course, the temperature outside is one of the most important things you can pay attention to. Tomatoes are considered tender vegetables (or fruits if you will), so they can’t handle too much cold weather.

How to Harden Off Tomato Plants

Before planting outdoors, you want to make sure your plants are ready for that completely new environment. Hardening off your tomato plants can help ensure they don’t die of shock within days of transplanting outside.

So how do you harden off your plants? You essentially want to slowly introduce them to the new elements before just replanting them in the ground.

Think about it. Your tomato plants have been growing in the perfect conditions – with the perfect amount of light, practically no wind, not many pests or insects, and no chance of getting sunburn (i.e. sunscald). You need to give them a bit of time to properly transition into their new environment.

This usually takes around 7-10 days to complete, and it can be a very time-consuming process. The idea is that you want to expose your plants to the outside elements a few hours a day, slowly increasing their exposure, until they are used to the outside elements.

This can be a painful process. I grow my plants in my garage grow room, and there are stairs involved. So I have to take these plants down the stairs, leave them outside for a few hours, and bring them back in, back up the stairs.

It’s not fun, but it’s a lot more fun than seeing all of your hard work die in a matter of days.

growing tomatoes in the ground

How to Plant Tomatoes Outside

Once you’ve let your plants get some exposure to the elements via hardening off, it’s time to get those babies in that beautiful Colorado soil!

It can be as simple as digging a hole, putting the plant in the ground, and covering up the roots. But one of the most important things I do is to remove most of the leaves except for the top 4-6 leaves, and then plant them in the ground.

Whatttt…?

You might have noticed those little hairs on the stem of your tomatoes. Well, those “hairs” will actually become roots if you put them in the dirt.

Removing those other leaves allows you to plant them super deep and makes the main stem of the tomato plant so much stronger.

Tomato Spacing

Tomatoes should be planted deeply and evenly spaced about 12 inches apart as they require lots of space for their roots to grow. They need at least 8 hours of sun per day. If you’re growing them in raised beds, you’ll want to leave 12-18 inches of space between plants.

When growing tomatoes in pots, just make sure your pot has a diameter of around 18-24 inches to give the roots enough space to grow.

Caring for Tomato Plants Outside

Tomatoes need full sun and well-drained soil to thrive. Water them regularly, especially during dry spells. Apply a layer of mulch around the plants to help retain moisture and suppress weeds. You can harvest your tomatoes when they are ripe (here is how to tell when a tomato is ripe), typically from late July to early October.

Watering Tomato Plants

Tomato plants need quite a bit of water. On sunny days, I usually try to water tomato plants in the morning, oftentimes every day. But when there are clouds or the temperature drops, they might not need to be watered every day.

Tomato Plants and Sunlight

For best results, tomato plants need 6-8 hours of sunlight a day. Of course, you can’t control the weather, but you can control where you plant them. Make sure you’re not planting your tomatoes behind a wall that only gets 1-2 hours of direct sunlight a day.

Before choosing a place to plant them, watch where the sun hits for a few days beforehand, making sure they will get enough light each day.

Fertilizer for Tomatoes

Most tomatoes are considered heavy feeders, meaning they eat a LOT. You usually want to fertilize your tomato plants when you first plant them, and then wait a while until later in the season. If your plants are showing signs of discolored leaves (purple or yellow), and/or curling up, it could be a fertilizer issue and they might need more phosphorus, nitrogen, and potassium.

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Fertilizer Type: Granulated
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Growing Tomatoes in Colorado

Growing tomatoes in Colorado can be so rewarding. A tomato sandwich or fresh salad with tomatoes from the garden is unbeatable! Make sure to start seeds indoors around 6 weeks before your last frost date, and transplant them outside when the soil temperature is above 50 degrees Fahrenheit. Happy planting!

chenell

AUTHOR, CHIEF GUACAMOLE CONNOISSEUR

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