When to Plant Vegetable Crops

Bryan Fischer, Horticulturist, Gardens on Spring Creek

An experienced gardener knows that timing one’s vegetable crop to its climate is one of the biggest make-or-break challenges of a growing season. These concerns are especially pronounced in our high-elevation region, where late-spring frosts can quickly turn to June heatwaves. 

If planted too early, cool soils and cold air temperatures often stunt plant growth, slowing down the crop or killing it – the opposite of what one would intend by trying to get a head start on the season.  On the contrary, planting too late forces transplants or seedlings to establish themselves as summer heat begins to set in, resulting in poor establishment and suboptimal crop quality – think woody root crops, fewer, smaller tomatoes and bitter greens. 

Thus, the key to planting your vegetable garden is to aim for the sweet spot that sits between temperatures that are likely too cool or too hot for sensitive, young plants.  While this is always a gamble, a generalized “crop timing scheme” like the one found below, can be a great starting resource to inform planting decisions. I’ve noted crops that perform best when direct sown (seeds planted right in the ground) and those that should be transplanted from seedling for our region. 

Crops that are best direct sown often have brittle stems or roots that resent disturbance during the transplanting process (like cucumber). Crops that are best transplanted require a longer growth period from seed to maturity. These crops (like tomato) are more productive in the Colorado garden with a head start on the season provided by transplanting. 

Crop Planting by Month for Fort Collins and Surrounding Communities: 

Average frost-free growing season: 151 days (May 4 – Oct. 2) *

*Keep in mind that these are average dates, meaning that Fort Collins receives a frost after May 4 in 50% of years. Fort Collins only receives a frost after May 16 in 10% of years. 

March:  Start allium crops (onion, leek) indoors – this can also be done in late February, also.  Start peppers, eggplant indoors.  Start brassica crops indoors (broccoli, cabbage, cauliflower, kale, etc.).  Start tomatoes indoors (second half of month).

Second Half of April:  Direct sow peas, arugula, lettuce and hardy root crops like carrots, parsnips, radish and beets.  Transplant your onion and leek sets as well as your brassica crops (broccoli, cauliflower, cabbage, kale, etc.)

First Half of May:  Complete the planting of any April crops.  Direct sow lettuce and other miscellaneous greens.

Second Half of May:  Once nights are consistently 50 degrees or higher (often last week or so), transplant nightshade crops: tomato, pepper / chili, eggplant.  Direct sow cucurbit crops: cucumber, summer and winter squash + zucchini, melon.  Direct sow beans, corn and potatoes.

Do not be tempted to rush these crops into the ground before night temperatures rise; cool soil and air temperatures will stunt their growth, offsetting the perceived time advantage.

June:  Complete the planting of any crops held for warmer temperatures that didn’t make it in the ground in late May.  Late in the month, start brassica crops indoors (broccoli, cabbage, cauliflower, kohlrabi, kale).  They can also be sown directly, but careful watering is crucial – consider covering with floating row cover to shade and reduce water losses from hot sun.

July / First Half of August:  Transplant brassicas late in month if started indoors.  Direct sow hardy root crops like carrots, parsnips, radish and beets.  

September:  Direct sow radish, arugula and lettuce.

October:  Sow spinach for early spring harvest and plant garlic cloves for harvest next year.  Both crops should be covered with leaves (can secure these with bird netting / landscape pins) or frost cloth.