Get Cool with Warm Soil

The vegetable cool-crop planting season is just around the corner.  Technically the dates are either two or four weeks from the last frost date (middle of May or so).  Hardy vegetables like peas, lettuce, spinach, arugula, onions and cole crops can be seeded or transplanted April 15 to May 15.  Semi-hardy veggies like beets, potatoes, carrots and Swiss chard can be planted from May 1 to May 15. But there’s no need to worry about following those time lines if you warm the soil now and use tunnels or cloches over the seed bed or transplants to keep them from continuous frosty nights below 40 degrees. 

I covered one of my raised beds today with black plastic and will keep it covered for 10 to 14 days.  If we get a long warm spell then I’ll take the soil temperature and if it’s 40 to 45 degrees, I’ll be seeding lettuce before noon that day!  Before putting down the plastic I started out by removing the heavy layer of chopped up leaves (read my mulch blogs from January about winter mulch).  I simply moved the leaves next door to my garlic planted raised beds.  They seemed happy to have the extra layer of protection and garlic doesn’t skip a beat with more mulch, those sturdy bulbs are pushing top growth already and they emerge right through anything.   
 

Black Plastic to Warm Raised Beds

After moving the mulch I made sure the ground was moist before covering with the plastic.  With recent storms, the beds were fine, if they had been dry, watering first helps create some humidity and heat below the plastic. I’ll keep you posted on my soil warming temperatures and seed planting. Below is a seeding and transplanting chart I put together for vegetable classes I teach in the Denver area. Everything is all relative to weather conditions so make sure your plan includes covering new seedlings or transplants. 

Vegetable Planting Calendar for the Colorado Front Range Add at least 2 weeks for higher altitudes For early planting (using Tunnels, Cloches, Cold Frames), move up all dates accordingly

 

CROP COOL SEASON	DAYS TO MATURITY	START SEEDS INDOORS	PLANT SEEDS IN THE GROUND	PLANT TRANSPLANTS OUTSIDE	FALL SEED
Arugula	30		April 15-June 1		Mid-Aug
Asparagus	Perennial			Plant root crowns April 15 to May 15
Beets	60-65		May 1-May 15		Mid-July
Broccoli	70	March 1-Mar15		April 1-May 15	Mid-July
Brussels Sprouts	80-95	March 1-Mar15		April 1-May 15	Mid-July
Cabbage	60-70	March 1-Mar15		April 1-May 15	Mid-July
Carrots	65-70		May 1-May 15		Mid-July
Cauliflower	50-55	March 1-Mar15		April 1-May 15	Mid-July
Cilantro	55-65	March 1-Mar30	May 1- May 15	May 1 -  May 15	Mid-July
Chard-Swiss	50		April 15-June 15		Mid-July
Celery	85-110			Fall planted best	Mid-July
Chives Onion	Perennial			May 15-June 15
Chives Garlic	Perennial			May 15-June 15
Garlic				Use Planting Bulbs	Mid-Sept Mid-Oct
Horseradish	Perennial			May 15-June 15
Kale, Collards, Mustard Greens	50-55		April15-May15		Mid-August
Kohlrabi	55		April 15-May15		Mid- August
Lettuce Leaf	40-45		April 15-May15		Mid-Aug
Lettuce Head	70-80		April 15-May15
Onion Bulb	100		April 15-May15
Onion Bunching	60-80		April 15-May15		Mid-July
Parsley	75	March 1-Mar30	May 1-May 15	May 1 – May 15	Mid-July
Parsnips	85-120		April 15-May15
Peas	50-65		April 15-May15		Mid-July
Potato Tubers	80-120		April15-May15
Radishes	20-30		April 15-May15		Mid -Aug
Rhubarb	Perennial			May 1 –June 15
Rutabaga	90-95		Early August		Early Aug
Spinach	30-50		April 15-May15		Mid-Aug
Turnip	40-75		April 15-May15		Mid-Aug

Vegetable Planting Calendar for the Colorado Front Range Add at least 2 weeks for higher altitudes For early planting (using Tunnels, Cloches, Cold Frames), move up all dates accordingly

CROP WARM SEASON	DAYS TO MATURITY	START SEEDS INDOORS	PLANT SEEDS IN THE GROUND	PLANT TRANSPLANTS OUTSIDE	FALL SEED
Basil	60-85	April 15-May 15	June 1-July 15	June 1 – July 15	July 1
Beans, Bush	45-50		May20-July  1		July 1
Beans, Pole	60-65		May 20-June 15
Corn, Sweet	65-80		May 20-June 15
Cucumber Slicing	48-72		May 20-June 15
Cucumber Pickling	58-58		May 20-July 1
Eggplant	60-80	March 15- April 10		May 20-June 10
Cantaloupe	85-120	April 15-May1	May 20-June 10	May 20-June 10
Okra	55-65	April 15-20	June 1-June 20	June 1-June 20
New  Zealand Spinach	50-60		May 20-June 20
Pepper	70-80	March 1- April 10		May 20-June 10
Pumpkin	95-110	April 15-May 1	May 20-June 5	May 20-June 5
Squash Summer	55-65	April 15-May 1	May 20-June 10	May 20-June 10
Squash Winter	55-105	April 15-May 1	May 20-June 10	May 20-June 10
Tomato	60-85	March 15- April 10		May 20-June 10
Tomatillos	75-100	March 15- April 10		May 20-June 10
Watermelon	75-100	April 5-15		May 20-June 10