Gymgirl: I love the temperature guide you posted. There are the Big Numbers at the top of each group. Then posted are the min. & max. numbers. What does the Big Number at the top mean. I don't quiet understand reading the guide.
Here's the reply from the lady who made these charts. The question was, "Is this AIR temperature or soil/ground temperature??"
Katherine: The charts are based on AIR temperature. I use these guides for two basic purposes. Starting indoors and direct sowing in the garden:
If I'm starting seeds indoors, the cool temps in the ‘seed starter’ chart are mainly to help me know when I can start hardening things off and get them out of this tiny room. It also lets me know which plants can withstand what (air) temps, and how soon I can get them into a cold frame.
I check the historic weather data in the Farmers Almanac for temperature in my area, then count back the number of weeks indicated on the seed packet. I know it's not exact science, but it's a good estimate.
If I'm direct sowing in the garden, I look at the germination chart to estimate when, by (air) temperature, I can start sowing, and how long it will take before I see anything popping up. Even in the garden, I’ll build a hoop house over my raised beds. If the cold doesn't creep back in, rain and animals will still mess it all up.
I'm in a strange climate (Chicago Zone 5 – COLD and WINDY). Hot/cold until mid-May. Last spring's early heatwave followed by another colds nap did a number on so many things. Plus, much of our stuff is in pots, so we don’t have the advantage of much ground heat. Thank God PVC, Plastic Sheeting, and White Sheets (resale shop) are so cheap.
We're constantly running around building shelter for the little guys. Cold snaps, 100 mph winds, drought, 100 degree temps for weeks. and that was all just LAST YEAR. I'm still always in awe at how much these plants can withstand."
I'm gonna give this a stab, to see if I can get this for you. Let's look at an example:
On the Germination Chart, if it is 32° outside, and you sow lettuce seeds, it will take 49 days for your lettuce to peep. However, if is is 77° outside, and you sow seeds, it will take only TWO days for your lettuce to peep!
On the Seed Starter Chart (let's use the blue box): 35° is the minimum safe AIR temperature that those veggies listed can withstand outdoors. (This is how our lady would know when to put her seedlings outside in her cold frame). In that same blue box, lettuce will germinate in 3 days with 75° air temperature, and 85° is the maximum air temperature at which you should attempt to germinate the seeds.
I think this is how it goes...LOL!
Oh, and I believe that it doesn't matter that she grows in Zone 5 (Chicago), because her research for these charts was done based on the relationship between the seeds and the optimum/minimum air temperatures.
I allways thought that days-to-germinate or days-to-emerge depended only on soil temperature, not air temperature.
And soil temperature depends on dozens of things that vary from place to place: heaviness and wetness of soil, shade, southern exposure/northern exposure, lattitude / sun angle cloudiness etc etc .
For example, poorly drained very heavy clay soil that was partly shaded on a north slope and far north lattitude would stay cold (soil temperature) for a long time after daily air temperatures warmed up.
But a raised bed with sandy soil in full sun, south slope and southern lattidue would warm up as fast as median daily air temperatures or faster.
I wonder whether her charts are valid only for her region, or give relative guidance for other regions.
One can read the guide from Spring at 42 degrees to summer at l05. But also from Summer l05 degrees to winter at 42 degrees. So if one seeds radish at 95 in the summer, temperatures will go cooler to winter so they will grow in the cool fall. Thats the way I read the chart.
Otherwise I just follow the recommended planting time chart for my area, works just fine for me. One extra step is to SOAK the seed BEFORE planting in soil or starting indoors; this method promotes faster, more even germination since the first step is for the seed to absorb water. Some additional steps are required for hard coat seeds and those with germination inhibitors.
Does this chart say if it is soil or air temp? I know there is a link above that is soil temps also. I printed it out the first time LisaP posted it and have been using it ever since. As of right now my soil is at the perfect temp to plant lettuce. I had older squash seeds they took forever to germinate, I thought it was due to their age, but they germinated in 3 days in the GH.