Posts Tagged germination temperatures
It’s all about temperature
Posted by piedmontgardener in Favorite Plants, Greenhouse growing, Native Wildlife, piedmont gardening on March 19, 2014
Some decades back, I remember an experienced gardener telling me that it’s time to plant corn when emerging oak leaves are the size of squirrels’ ears. Being of a more scientific bent, I did a bit of research and discovered that corn likes a minimum soil temperature of 50 degrees Fahrenheit. I’ve since found that corn germinates better for me when the soil is closer to 60 degrees.
But there’s truth to that old gardener’s advice. Over the years, I have observed that my soil temperatures reach 55-60 degrees just about the time the leaves of my tall oaks reach the size of squirrels’ ears. It varies a bit, depending on which species of oak and whether the oak is growing anywhere near the garden plot, but, in truth, oak leaf size and soil temperatures do seem to reliably correlate, proving once again that a gardener always fares better when she pays attention to the environmental cues surrounding her.
Especially in late winter/early spring (I can’t tell them apart this year), soil temperatures are critical to the success of my spring vegetable garden. Spring vegetables have a lot going against them in my region most years. Winters are often very wet, making for soils too wet to work. Or, like this year, repeated blasts of icy precipitation keep the soil not only too wet, but also too cold for planting. The sun is supposed to return with warmer temperatures just in time for tomorrow’s vernal equinox, and I know I speak for all frustrated southeastern gardeners when I say, Hallelujah!
But that’s the other tricky part of southeastern springs. Most years, they don’t last very long, instead morphing into summer by late April. Spring vegetables dislike summer heat as much as they are averse to freezing rain. It’s a flat-out gamble whether I reap much edible at all most years. But to be without the crisp freshness of just-picked greens or carrots, or the earthy sweetness of a red beet or onion — that’s too cruel a fate for my winter-worn green-craving palate to contemplate. And so I gamble/plant.
My lettuce and spinach seedlings in the greenhouse were mostly large enough for transplanting a week ago, but another round of freezing rain forced yet another delay. I am determined to plant them out in the next few days. I’ll pray that the row cover I enclose the transplants in will protect them from any last-minute jokes from wintry weather. Here’s what they looked like last Friday:
The local agricultural college near me publishes all kinds of useful information about gardening, including this handy chart of vegetable varieties and the minimum soil temperatures required for germination. From it, I see that lettuce and spinach seeds need 45 degrees. If you look at the top photo in this post, you’ll see that the soil temperature in my future lettuce bed was hovering at around 50 degrees last Friday. The ice storm of yesterday may have dropped it a bit, but for transplants, I’m not worried. In a couple of weeks, I’ll direct-sow additional seeds into this bed for what I hope will be a more prolonged harvest — if summer temperatures delay their arrival long enough.
This year, I’m growing a few varieties that I’ve had success with before, and a few new ones. I’m always looking for more heat-resistant varieties of greens. Here’s what I’m trying this year, all from Johnny’s Selected Seeds:
- Red Cross — A heat-tolerant butter head lettuce that produced spectacularly for me last year. It was also delicious and really handled the heat well. As the name hints, its leaves are a beautiful red, which I love.
- Buttercrunch — Really tasty and sweet, and reasonably slow to bolt. Leaves have enough body to work well as lettuce wraps, but are tender and sweet enough to eat by themselves. Yes, I’ve grown it before.
- Annapolis — This is new for me this year. I couldn’t resist the description of what is supposed to be their darkest red romaine lettuce. Who doesn’t love romaine lettuce?
- Coastal Star — Another romaine, one I’ve grown several times now because it is reliable and wonderful. Sweet, dark green leaves that stand up to warming springs better than I could have ever hoped. I love this lettuce!
- Corvair — Spinach comes in two forms. Some are smooth-leaved, and Corvair is one of those. This is a new variety for me. It is purported to be a slow-bolter and resistant to mildews. Less wrinkled spinach leaves means less washing required, so I’m giving this one a try.
- Tyee — This is a savoy spinach — the wrinkled-leaf kind. I’ve grown it for years because it is tasty and vigorous. Its rapid leaf production compensates for its tendency to bolt when temperatures begin to warm.
- Arugula — The standard salad arugula. I’ve grown all sorts of mesclun greens in past years, including this arugula. They all bolt at the first hint of 80 degrees. Despite my fondness for these tangy greens in my spring salads, I confined myself to just this type this year. I’ve composted way too many bolted mesclun greens in past seasons. This year, the arugula will have to suffice to provide that contrasting zing to the sweetness of the lettuces and spinaches in my salads.
Earlier this week, my onion plants arrived. The Yellow Granex plants will get tucked in at the same time I transplant the greens. Again, I would have popped them in before now, but all was ice again just yesterday.
According to that chart link above, carrots only need 40 degrees to germinate, while beets need 50 degrees. I’ve found that when I plant carrots when my soil is 40 degrees, they sit and wait until the soil is warm enough for the beets to germinate. I’ll use my handy dandy soil thermometer to check their future beds this weekend. If I’m at 50 degrees or better, I’ll try to get those seeds in the ground too. This year, I’m trying:
- Romance — This is a new carrot variety for me, advertised as delicious, high-yielding, and uniform. I couldn’t resist.
- Nelson — This consistently sweet early carrot (Romance should mature later) is a reliable old friend in my garden.
- Red Ace — I’ve tried other beet varieties, but this is the one we love. Always productive, magnificently sweet and tender. We love these beets!
That’s it for the spring garden. If I see any healthy broccoli plants at the local agricultural supply store, I may grab a few, per Wonder Spouse’s request. I rarely have great success with spring broccoli — that summer heat problem again. But it will be easy to add a few beneath the tented lettuce bed, where cabbage moths can’t reach them to deposit eggs.
I’ve also given up on spring peas. They are so very heat sensitive, and our winters are so up and down that I rarely get a crop worth my effort. If we have a craving for spring peas, we can always grab a few at the local farmers’ market.
The greenhouse is getting full of seedlings. All my tomatoes and peppers are well up, but still small, of course.
I’ll tell you about them another time. I’ve got lots of flower seedlings growing too. Some kinds take almost two months to reach transplanting size, so I must start them early.
Wonder Spouse will be creating his potato bags this weekend. He would have planted them sooner, but that pesky ice slowed him too.
Every year, my blog view count increases as people search on things like, “When can I plant spring vegetables?” You will find charts of average last frost and freeze dates, but I consider those rough ballpark estimates. Every yard is different, thanks to variations in microclimate. The best way to know when to plant your spring vegetables is to pay attention to what your garden area looks like during late frosts. Is it snowy white? Then you’re in a cold spot. Err on the later side of the planting range.
To be much more confident, invest in a soil thermometer and use it. They are not expensive. Mine even comes with its own little case with a clip for attaching it securely to a pocket.
I know that the wildlife in my yard is even more ready for spring than I am. Two days ago, as a cold rain began morphing into freezing rain, a frustrated Red-shouldered hawk actually parked itself on top of my bird feeder for about ten minutes. It looked so hungry and frustrated that if I had had something to feed it, I would have tried.
We’ll make it, friends. Spring is tantalizingly close now!