Sowing success a matter of temperature

In an annual ritual of spring, gardeners emerge from their houses in mid-March, blinking in the thin sunlight as they peer around the landscape, assessing what needs pruning, cleaning, or mending.  All it takes to get our sap rising is for the month to turn to March, and we shrug off our winter lethargy in favor of planting the garden.

 That harbinger of spring acts like a jolt of electricity on our minds, sending a surge of energy urging us to get our hands in the soil and sow seeds.  But if you’re too quick to cave in to eagerness, you might find that your good intentions are not appreciated by the seeds you lovingly pop into the ground.  They’re not impressed by the calendar; they could care less about leprechaun and daylight savings.

 What the seeds want is warmth.  To ensure seeds sprout instead of sulk, gardeners need to plan on two things: frost date and soil temperatures.  Average date of last frost is what most rely upon to plan their plantings; it’s calculated from 30 to 40 years of data.  In Boulder the probability of frost is 50-50 on May 3, in Loveland May 4, and Longmont May 5. 

 Because it’s still possible to get frost after these dates, many gardeners prefer to use the 10-percent probability of frost date as their benchmark, which in Boulder is May 13, Loveland May 16, and Longmont May 17.  You still need to plan for protection from the odd cold snap, but the likelihood of frost is much less when waiting until mid-month.

 Yet there is a second temperature factor that Colorado gardeners shouldn’t ignore: soil.  Chilly soils will limit germination of seeds, and if the ground is both wet and cold, seeds will rot instead of sprouting. 

 Early spring vegetables vary in required soil temperatures.  Spinach and lettuce are the most tolerant, needing soil to be 35-degrees to germinate and 45-degrees or warmer to grow well.  Peas, chard, onions, mache, and parsley can grow in soils at 40-degrees, but do best in soils of 50-degrees or warmer.  Soil temperatures of 60 degrees or warmer are perfect for fava beans, beets, carrots, and leeks, while scallions, Asian greens, kale and kohlrabi like is slightly warmer, at 65-degrees.

  Can these plants germinate in slightly cooler soils?  Yes, but for them to grow rapidly and thrive – key to sweet flavor and tenderness – gardeners should pay close attention to bringing soil temperatures up.

 To do this, plastic mulches or water-filled walls are helpful.  If you’re choosing to go with warming by plastic, clear plastic works better than black at warming soil, bringing the temperature up 10 to 15 degrees in a few days. Make sure you weight down all edges of the plastic to keep it from blowing in the wind, and lay it out so that it touches the soil a week ahead of planting to give your seeds a warm start. 

 Punch holes into the plastic to sow seed if you plan on leaving the plastic in place over the season.  If you are removing the plastic once temperatures are stable, laying the sheets down in strips that can be folded back for planting space is a good way to leave the plastic between rows for a few weeks.  If using water-filled walls, place them out one week before planting to help warm the soil.

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No peas for St. Patrick

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The answer is no.

This pains me, because that answer flies in the face of years of tradition.  But despite the calendar and my family’s full-throated observance of St. Patrick’s Day, I did not plant peas in the garden.

The reason for this is simple:  I’ve become suspicious that the cold shoulder the soil gives those seeds slows their germination.  This delays the peas’ entrance into the world, dashing my hopes to get the season rolling.

Though they’re a cool season crop, perfect for spring and fall gardens, peas are a bit of an anomaly.  The plant likes it chilly, but the seed prefers it warm, with best germination at 50 to 75 degree soil temperatures.  True, they’ll sprout if the soil is as cool as 40-degrees, but at those temperatures, peas take their time.

My soil is registering a flat 50-degrees on the thermometer I shoved into the raised bed, which is why I vowed to wait an extra seven to ten days; to give the soil time to warm before sowing. 

What it boils down to is an experiment between my desire to plant and my resolve to wait.  At this point, it’s a toss-up as to whether I can fight the urge; like a dieter determined to keep their mind off of food, I’m distracting myself with odd jobs, writing, and reruns of Glee.

If you held onto tradition and planted peas, give them some water and patience.  If they seem a bit slow to start, don’t give up on them.  We’ll compare notes in a month or so, to see whose plants are further along.

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Sowing Onions

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Today’s post can be heard on the public radio show Crop to Cuisine, hosted by Dov Hirsch.

As you’re planting your spring kitchen garden, leave room for one of cooking’s basics that’s delicious enough to bring tears to your eyes.  Growing onions in Colorado is easy, and if you want to add this allium to your vegetable plot, the time to get planting is now.

Seeds, seedlings and sets are available to the home gardener, so here’s a quick primer on the difference: seeds are directly sown into the garden from mid-March through the end of April and are very successful in Colorado.  Sow them shallowly, about three-eighths of an inch deep. 

Seedlings are started plants, grown this season and not yet mature enough to begin forming bulbs.  Locally, onion seedlings are readily available in small clumps that you tease apart upon planting.  Plant them one inch deep and slightly later than seeds, so any time in April will do.   

Sets are onion bulbs that are about one inch in diameter and planted as you would a tulip or daffodil.  Both seeds and seedlings can be used for green onions, often called scallion-stage, or for sizing up into storage bulbs.  But if you use sets, keep in mind that they’re best if you want bulb onions. 

 Look for long-day varieties that form bulbs once we have 14 or more hours of sunlight daily; in our area, onions will begin producing pungent, sweet bulbs beginning in July.  

 Onions prefer fertile, well-draining soil liberally amended with organic material.  Spread compost one to one-and-a-half inches deep across the bed, then till it in, working it eight inches into the soil. 

 If you’ve sown seeds, thin them once the seedlings have five leaves.  For best bulb production, thin to three inches apart.  Pulled seedlings are delicious as fresh or grilled; eat them as you would a scallion.  As your onions grow, each leaf they put on represents a ring in the bulb itself, and size matters: larger leaves mean bigger rings.

Water them frequently, never allowing their shallow roots to dry, which can cause bulbs to be stunted and tough.  Onions are nitrogen-greedy during the first part of the season, so fertilize until mid-July, then put them on a diet – onions don’t need much nitrogen past that point. 

As onions bulb, they often push themselves out of the soil; this is normal and your plant will be fine.  Avoid giving in to the urge to “hill-up” your onions; hiding the beautiful bulb will work against the plant’s desire to plump it and you won’t get good production.  As the plant prepares to bulb (the neck will feel a little soft), if your soil is hard from the summer sun, gently loosen it to let the plant expand.

Keep weeds to a minimum, since they rapidly crowd out the less-vigorous onion.  Careful, shallow hoeing around the plants is a must to avoid damaging the developing bulb, so if you’re a bit of a brute with the hoe, mulch is a good option for your onions.

Thrips are common insects in our area, rasping off the surface of the onion leaf, leaving a tell-tale trail of silver.  They hide out on weeds, so weed suppression is key to control.

You can tell if your onion is mature by its floppy tops, which start laying over in mid-August.  Hold off on watering at this point and when most of the tops have fallen, gently lift the onions from the ground. Let them rest on top of the ground for up to two days, trying to keep them oriented the same way they grew in the ground to prevent sunburn.

After two or three days, take the onions into a warm, dry location to cure for several weeks until the necks are completely dry.  Trim the tops, then store the bulbs in a mesh bag out of sunlight in a cool location.

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Plant your inner chef

Today’s post can be heard on the public radio show Crop to Cuisine, hosted by Dov Hirsch.

Obsession is such an ugly word for what can be the most rewarding experience to give your stomach.  Sure, a few hours spent planning, a month or more spent purchasing and utter devotion to soil and sowing may seem an addiction, but for kitchen gardeners, the rewards are worth the time.

 It’s not about putting food on the table; it’s about putting in endless combinations of tastes and dishes.  Getting months of harvest to come together in a culinary crescendo takes exquisite timing and if you want to foray into gastronomic gardening, the time to get started is now.

 Unsure how to begin?  Here’s a guide to planting your inner chef this month:

Beginning in mid March, direct sow seeds straight into the garden.  Creamy-crunchy lettuces, sweet spinaches, beets and carrots in purples, golds, and oranges pack your spring garden with flavor if sown directly into the prepared bed. Turn an inch of compost into the soil, break up the clumps and smooth the bed.  Small seeds like shallow sowing; sprinkle them out and cover with a dusting of soil.

Try slow bolting Ben Shemen lettuce, developed to take the heat in Israel, stays sweet in Colorado’s blast oven summer.  Two-toned Purple Dragon carrots and golden beets are pure table chic.    

Pre-sprouting peas at warmer indoor temperatures gets them started for growing in cool weather.  To jump start peas, place them between damp paper towels in a warm place, and check them several times per day to keep the towels damp and to look for germination.  Once they’ve sprouted, pop them into the garden, two-inches deep and three-inches apart.

Choose taller varieties to trellis if you have little space– they give you more peas than compact varieties.  Change up your ideas on peas by planting both Sno peas – that you eat pod and all – and shelling peas, for perfect round balls of flavor.  

Perennial rhubarb will produce succulent stalks year after year once established.  But be patient and don’t cut the leaves the first year they’re planted.  Put rhubarb in a sunny spot where it can stay; this plant can easily live up to 30 years.  Space them 34-inches apart, deep enough to have the top of the crown two-inches below the soil. 

Start seedlings indoors.  Warm season plants such as tomatoes, peppers, eggplant, or cucumbers give earlier production if started indoors six to eight weeks before planting.  Cole crops like cabbage, cauliflower or broccoli are sweeter started early because they are planted in time to take advantage of our cooler, moister spring.

Keep these tips in mind when starting your seeds:

 – Choose an out of the way, sunny location to place your tray over flooring that can get wet or dirty.

–  Moisten light, sterile seed starting mix before you fill small pots or cells.  Get the mix damp but not soggy.

–  Sow seeds and cover with slightly damp mix, then place a plastic tent or dome over the tray to raise humidity until germination.

–  Once your seeds are up and growing, remove the humidity tent, but do so gently over a few days – a blast of cold air can shock seedlings if the tent is taken off too quickly.

– Keep lights within three inches of the seedlings as they grow, but don’t let the plants touch the light.  Raise the lights as the seedlings grow to keep them above the plant.

–  Feed with half-strength fertilizer after they get their second set of true leaves.

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