Spring into Planting: Veggies to Grow Now!

By Bryan Fischer, Curator of Plant Collections | The Gardens on Spring Creek

This time of year, many gardeners are antsy to get their hands dirty. Still, soil and air temperatures remain too cool for many crops to go in the ground. Gardeners should plan to hold their warm-season transplants indoors until at least mid-May, or better yet, when soil temperatures reach 50 F. Cool-season crops, on the other hand, can be direct-sown and transplanted now (mid-April), as they grow best in spring and again in fall. Such crops include brassicas (cabbage, broccoli, kale, mustard greens, arugula, radish, and others), onions and leeks, peas, carrots, and beets (plus Swiss chard, which is actually the same plant bred for leaf rather than root development). Hardy herb transplants can also be planted at this time if they are properly hardened off first. These would include parsley, chives, lavender, thyme, and others, but hold the basil, rosemary, and cilantro until temperatures are truly warm. Basil should not be exposed to temperatures below 50 F, either air or soil. 

As for our hardier vegetable crops, prepare a bed by lightly turning the soil, if needed. Add compost or other organic matter like dried leaves into the bed at this time. Alfalfa meal or pellets, which are slow-release sources of microbial food and nitrogen — the most commonly limiting nutrient in our region’s soils – can be an excellent addition. Pellets are a particularly cost-effective fertility amendment for those gardening on a larger scale. Simply wet them with a sprinkler to break them apart before tilling them in. 

For direct-sown crops, make a seed bed by preparing a planting bed for transplants. Then, take a grass rake and break up any chunks of soil, making the surface smooth. At this point, you can sow seeds twice as deep as the seed is wide. You will likely need to water daily if the weather is sunny or windy, though less so if days are cool. Direct-sowing works well for crops with tap roots and those with brittle stems, like carrots, radishes, peas, beets, and chard, as well as many hardy herbs. Seeds will be slow to germinate due to cool soil temperatures, but this method is preferable to transplanting for these crops that transplant poorly. It’s also less work than starting seeds indoors. Despite their slow starts, some of these crops are quite quick to mature; radishes can go from seed to harvest in just over a month, making them great first vegetables for kids who want to garden.  

Brassicas are often best transplanted in spring; while they grow best cool, they germinate most successfully with warmth. I germinate mine with a seedling heat mat equipped with a thermostat and probe and remove them from the heat mat immediately after germination. If you don’t have these tools, you can germinate cool season seeds in a sunny window just fine — they just germinate more slowly. Germinating without a heat mat is far preferable to germinating and trying to grow them on a heat mat, which will result in “leggy,” floppy plants prone to breaking. If you go the heat mat route, remove seedling pots as soon as they have germinated. Plants can be hardened off once they have two or more sets of true leaves (the two leaves that appear at germination don’t count) by setting them in a cold frame for a week or two (adding some water jugs will insulate the frame significantly), or by moving them outside into a spot with afternoon shade. In the case of outdoor hardening, set the seedlings out for just a couple of hours the first day, adding a couple hours each day until they can make it a whole day outside in morning sun and afternoon shade—they are then ready for transplant. The appeal of the one-and-done cold frame tactic becomes more apparent when you consider the difference in time and hands-on labor needed to harden plants off in such a manner. 

Similar tactics can be employed with hardy herbs and onions if you want to grow them from seed. Be sure to sow these transplanted crops indoors during March to be on track for spring. If you miss this window, or don’t want to fuss with seedlings, you can also buy these starts at the nursery; just be sure to ask if they are hardened or not so you know where to put them when they get home. 

Whether transplants or direct-sown seeds, spring crops benefit from a bit of protection during extreme weather events that seem to be intangible parts of a Colorado spring. If particularly chilly temperatures are forecasted, I’ll cover my young plants with a layer of frost blanket, available at the nursery. It will last a decade if stored properly. And remember, hold off on any tomatoes, peppers, corn, beans, melons, or the like until at least mid-May when temperatures are more appropriate for their growth. Regardless of why you may choose to grow your own vegetables, you’ll find that it is a rewarding process, and that taste and texture from storebought produce just doesn’t compare.