If charts and graphs don’t get your blood pumping, you might want to skip this post. Gardening is about to get very geeky.
So, I found this very locally specific vegetable planting guide put out by the Wyatt-Quarles Seed Company in Garner, NC. This information, of course, is only handy if you happen to live in the North Carolina piedmont. Since, I do happen to live in the North Carolina piedmont, I have been a little bit obsessed. The planting dates suggested are waaay earlier than the dates I calculated off my seed packages based on the last average frost date.
Our last average frost in Durham isn’t until mid April, putting the generally recommended outdoor planting date for even the coolest weather crops well into March. But the WQ planting guide recommends planting crops like spinach and carrots and cabbage as early as February 1st.
So, being the dork that I am, I looked into this discrepancy and discovered the world of soil temperature. Obviously, low air temperatures dictate which tender green things are able to survive the early spring, but lots of cool season crops can handle some light freezing. It’s actually soil temperature that dictates which seeds can germinate.
It’s really easy to find information on optimal seed germination temperatures because it is an extremely straightforward experiment. How long does it take seeds to germinate at 40 F, at 50 F, at 60 F, etc. How many seeds ultimately germinate at each temperature. The intersection of maximum percent germination and fastest germination is the optimal germination temperature.
But, the optimal germination temperature for many seeds is crazy high. If we waited for soil temperatures to reach 80 or 9o degrees before planting, nothing would ever mature before the fall. Luckily, I found this handy chart on the Natural Gardener.
It outlines the practical soil temperatures for planing seeds. The temperatures at which a reasonable number of seeds will germinate at a reasonable speed and still leave you time to actually grow vegetables.
I kind of want to get a thermometer for my dirt now. Luckily, there are also some really cool soil temperature maps avaliable online. Here is today’s:
We are in the dark green belt that represents 50-55 F. Meaning that soil temperature wise it is practical to plant everything from beets to tomatoes on the chart above. Of course tomatoes are delicate little things that collapse at the first sign of frost, so I won’t be planting tomatoes until at least April.
But, I planted peas last weekend, and I planted broccoli (Packman seedlings from Lowes), onions (“yellow” sets from Lowes) and carrots seeds (organic Scarlet Nantes from Burpee). I also replanted the lacinato kale and two strawberry plants that over wintered from last year’s garden. They were all temporarily relocated to my kitchen floor while I picked up last year’s bags and tilled the topsoil into the new in-ground bed. David is very happy with their new location.
I’m also holing back some garden space and seeds/sets to plant a bit later as an experiment.