Figuring Out When to Plant Crops

This thread is a spinoff discussion that began in another.

How do you know when to plant your crops when you are either unable or unwilling to follow the conventional planting guidelines?

Brought up so far are eco signs (other common plants sprouting, blooming, etc., or other natural and regular phenomena, occurring at the time you should plant such-and-such crop), taking soil temperature readings (which for newbies, requires sifting through a lot of conflicting information, and for others, may not be useful due to extreme soil temperature swings daily), and good ol’ trial-and-error (which uses up a lot of seeds). Anyone want to expand on these methods, or bring up new ones?

Personally, knowing when to plant crops has been especially relevant because I’m trying to direct sow crops that are bred and expected to be started indoors as transplants (tomatoes, peppers), and my area (central inland FL) doesn’t play nice with national planting instructions. Specifically, there is an important difference between conditions right for germination, and conditions right for growing, which is glossed over or seemingly forgotten in mainstream planting advice.

For instance, I found out that many “cool season” crops actually love germinating at the 70-86 degree range (charts from Oregon State University and University of Florida). Do they grow well at those temps after germination? Dunno, haven’t tried yet. Most of the internet would tell you no. But it sure makes things confusing for newbies like myself.

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My neighbor just bought great seeds from a recommended bio company and complained to me they had failed. When i asked where her garden is she just pointed at a mish mash of blackberries. She had chucked thèm in and expected thèm to grow. She said she failed because of what the government is spraying.
I told her they apparently forgot to spray mine.

I’d be happy to just chuck seeds down, but it took time for me to get there. Most plants i have to use plastic pots for starters. I might just be a shitty grower, but that’s how it is.

1 get something going using boring conventional methods and save seeds from the best plants
2 seed exessively next season pushing limits.( you got tons of seeds now!)
3 scout for volunteers in your beds and definitely take care using their seeds next season, mixed in or outdoors.
4 let some selfseed next next season.

Yup three years minimal.
Plant breeding takes time.


Absolutely it does take time, lots of time. For a beginner I think the most that can be done in just three years is discovering those crops and varieties that do at least well enough to produce your own seeds. You can get clues about that by looking around your neighborhood and seeing what other people are growing. If farmers markets are available, first confirm that the produce was truly locally grown, and you will know it is a viable crop. Also, a lot of seed can be harvested from the produce you might buy there. Tomatoes, squash, melons and other things for examples will have lots of seeds you can save, and you’ll know they have at least one year of adaptation to your climate. When the crops that do grow well, and that you like, have been identified you can study seed seller’s webs sites and catalogues and for information on specific varieties and purchase those that sound like what you are looking for. *Just keep in mind that variety descriptions are just marketing and often a bit glorified and exaggerated, still some useful information can be found, for example, when adding something specific to my collections I like to compare days to maturity between offerings and tend to purchase those with the shorter DTM, within the species. Joining seed trades such as the one here can help get a jump start on collecting diversity at minimal cost, just the shipping.

Trial and error and the experience that comes with it is in my opinion the only way to learn how to garden. And yes, it will use up a lot of seeds, and time, instant gratification is extremely rare. If I start with a new species and it fails to produce the abundance of seed, I need to go on with selection and breeding with in just a couple of years, I drop it and move on to something else.

I’ve been gardening for nearly sixty years, in different micro-climates but of the same regional climate, the work of selection, breeding, improving and learning never ends.


For me in far north it’s quite easy. Our summer comes fast and even if it’s not ideal weather, atleast frost becomes as rare as it ever will very fast. Start for warm weather crops is within 2 week period every year and possible delays are within forecast range almost always. Even week too early is way too early. Cool weather crops are couple weeks before that, but those can take even worse weather. For warm loving plants I monitor ground temperature (if necessary). Target is that ground temperature is +15C (59F) at 20cm depth and stays there, but can’t be that picky here. Will take slightly lower temps too if year is far enough and weather reasonable. Measuring ground temperature deep gives you better indication where it’s going to be in long term. Since you probabably don’t have such obvious season change you might need to play it a bit more save with ground temperatures and don’t expect good times to last. Also it’s good to be aware where are your frost pockets and make high beds that can reduce frost to some degree

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Awesome. We seem to have a very long period (or maybe that’s just subjective, I didn’t time it) here where the weather swings up and down between extremes, getting to 80’s then dropping to below freezing. I’ll know to watch it for next year, but I lost a whole lot of plants this year due to it. Live and learn.

Yes! This is my question, because it’s my first year doing all this and I don’t have an experiential reference for what soil temperature will look like during summer. Right now soil temp hits 79F (26C) mid-afternoon but is lower the rest of the day and drops to about 65F (18C) (have only been able to take one reliable reading so far) during the night. Some material online says plants require that nighttime drop; many don’t mention it at all; I assume indoor transplants stick to a steady constant temp of 80F or something. So by “stays there,” are you including nighttime temps, or do you mean mostly daytime temps?

I operate under the assumption that climate change is going to be messing with our tried-and-true weather patterns from here on out, getting progressively worse as the years go by. I also assume that I’ll eventually be able to landrace crops that can handle new weather incrementally and I won’t have to pay such focused attention on details like soil temp. It’s just this first year or two, and getting down the techniques and background knowledge. I don’t like to just follow directions; I like to know why they’re important directions to follow in the first place, lol.

@Logan_zzz333 You should get little less swings if you go deeper. 20cm is quite deep undergroung even though it feels so short in everyday live. It’s possible that there day swings affect deeper, but it should still be less than closer to surface. Mininum is what you are looking for anyway. That tells what kinda heat stores you got there. Here you might get well over +20C (68F)surface, but +10C (50F) at 20cm which tell that even the surface will be closer to that during night. Also cooler period will be more severe. If ground is warmer deep down it takes quite alot to cool down. +15 (59F) is kinda general minimum recommened for most warm loving plants, but it’s not really ideal in long term. +18C (65F) is ideal minimum for atleast tomatoes and peppers (maybe not including chinense peppers). So small differences in ground temperatures make big difference. Haven’t made measurments later in the year that often, but my estimation is that peppers here really get going once it hits that +18C. Tomatoes don’t need as much, but even they don’t grow fast if it’s just that +15C. Under that it very fast turns into struggle for survival. Air temps they take till freezing as long as ground is warm enough. I’m not aware that plants need temperature drop during night. Think mostly they will do with what they got. Something like rocoto peppers almost require swings to produce, but that’s because they originate in the highlands.

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Interesting… Won’t checking so far down be away from where the seed itself is trying to germinate though?

It’s more to get general idea of long term conditions. Daily surface temperatures are so dependant on daily conditions and it really doesn’t matter as much if it’s +20C or +25C in surface. They germinate faster, but there is no danger. Temperature deeper tells how low surface is likely to go during night as there is more constant temperature that starts warming surface once it’s below temperature deeper down. Because there is so much heat stored in the ground it takes so much more energy to cool down the whole soil layer and that’s why at some point surface doesn’t cool down as fast as in early evening. You can go meters down and the temperature doesn’t change that fast. You said you had lows of +18C, I would guess you will have similar temperatures if you go down futher whether it’s day or night. You can also take morning readings, but that is more affected by how cold/warm previous night was and next morning it might be colder than that. I do take readings closer to surface also to get idea how much help there is during day. Still it doesn’t help if surface is warm during day, but night is cool enough to possibly cause damage.

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Thank you :slight_smile: That’s making a lot of sense now.

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Just took a reading around 8 in the morning, about 6.5in (17cm) down, and got 61F (+16C). We’ve had cold, windy, rainy weather the past few days. Also, I found this website (Florida Automated Weather Network by UFL) that shows underground sensor readings for the Florida state, you can narrow it by your specific area, and it shows a history of readings too. I’d imagine there are resources like this for places everywhere, for those interested but don’t want to or can’t take their own readings.

I’m nearly a thousand miles north of central Florida. Right now, I have radishes, carrots, onions, peas, lettuce, potatoes and a few other things already direct seeded outside and growing well. I did use a plastic cover over the onions and carrots, but that was mostly to protect them from being washed out in case of a downpour. Volunteer tomatoes are up, but not out of danger of a later freeze, all those other things I expect will be fine. I have a brassica landrace project planted last fall that is doing very well, having survived -14 F, -25C a couple of days before Christmas.

I’ve never measured the actual soil temperature. I plant things like those above when it starts staying above freezing for days at a time. Now it’s getting into the high 70s to low 80s and mostly above 50 at night. Things that fifty years ago I would not have planted until mid-May will be going in the ground very soon. In recent years I’ve seen days in the 80s still be punctuated by below freezing temperatures, but I have plenty of seed to start over if necessary.

It is a new climate with new challenges, that’s for sure. I’ve gotten used to spring coming warmer and faster and to it intermittently going back as cold or colder than it ever did but one morning last week, it was 74 degrees at dawn. That’s the most extreme morning temperature at this time of year I think I’ve ever seen. I worry that it isn’t a good sign.

The minus 14 F before Christmas wasn’t the coldest I’ve ever seen but it was almost 60 the evening before. If it dropped 70 degrees over a couple of days, I wouldn’t think anything of it but 70 degrees in ten hours sort of freaked me out.


That looks like a good tool. I always enjoy good data. It makes vizualizing what’s happening a lot easier. Would be interesting to know the depth of that measurment. It does look like it’s fairly deep since fluctuation isn’t that severe. The last few days really makes my point. Even with cold weather it goes down slowly. I would guess that at the end of that period surface temperature is fairly close to what it is deeper down whereas during warmer days it is closer to air temperature highs. We do get that kinda swings usually few times during summer so even warm loving crops should be fine for you this time of the year. Weak will die and strong will survive. Same swing month earlier with lower heat storage might be pushing the limit since saving warm periods might not be as warm or long and cool periods might come one after another. It’s all about learning realities of your climate.

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Here last frosts used to be on May 14th, and starting from May 15th everybody planted out tomatoes and other warm loving crops. It no longer works however, because after a heat wave in the second part of May, we started to have quite severe night frost somewhere between 28th May and 6th June. If you are not covering your seedlings planted just after May 15th, your game might be lost. Both long term data, phenology and measuring soil temperatures are getting less reliable with the changng weather patterns, being more extreme every year. So planting out crops has become more like a lottery on one hand, on the other hand it has given us a lesson to divide the work and to plant at 2-3 different dates, and always keep a backup of seedlings. Pretty much the same applies to direct sowing but this is more important with crops grown from seedlings.


In case this helps, I planted cold weather crops – brassicas, peas, and fava beans – outside in early January and February.

Most of the peas and fava beans lived, but didn’t sprout until early March. Some of them sprouted in January, which was awesome, but then they stayed tiny little sprouts that didn’t get any taller until March. (They did live through all the massive quantities of snow, though!)

Most of the brassicas sprouted in late January, but died after being buried under six inches of snow for two weeks. I had to replant brassicas three times, and they’re still just small seedlings.

Overall, I don’t feel like planting them in January gave me that much of a head start. Maybe it will someday – I would love to select for crops that can grow through the winter and not just stall and survive – but for right now, I suspect that planting before February won’t make any difference for me.

The one exception is the ones I sowed under a mini greenhouse in January – they’ve grown a bit more than the ones I just left out to the elements! It’s not much – maybe two months’ worth of growth in winter equaled a week’s worth of growth in summer – but a week’s head start is a week’s head start, and I’ll take it.

So I probably planted too early, but I’m not sure if that would be true in a normal year. January may have been right for the fava beans and peas in a normal year. They did (almost) all survive!

The brassicas may prefer to be planted a month after the peas and fava beans. I don’t think anything lived unless it was sowed in late February to mid March.

I will say that this year was unusual. We usually get our last snows in March, and they’re light. This year, it snowed heavily all through March, and we had a huge blizzard on April 4th. Now it’s an early, blazingly hot summer. Joy.

I suspect in a normal year, sowing in January would have given me a much more significant head start, because there would have been far less snow covering the winter crops and blocking sunlight.

Now, for the opposite – when is too late?

Well, last year, my first time trying cool weather crops, March was much too late to plant brassicas, because it was already too hot and dry for them to germinate. So I’m starting to think early to mid February is the best time for me to plant cool weather crops here. Sometime in that range when there’s not snow on the ground, and there’ll be a stretch of warm-ish weather for several days straight.

Meanwhile, with warm weather crops, “too early” is probably before May 15th if you want to grow divas that can’t handle a few very light frosts that may or may not happen after April 15th (our average last frost date). I want to select for warm weather crops that can deal with a light frost or two. That’s a month of valuable growing time, the only time of year with warm temperatures and abundant water left in the soil, so I want to use it. So I plan to plant them then, whether or not I “should.” Most of my neighbors wait until after May 15th.

With warm weather crops, “too late” is probably late August / early September. Our average first frost is October 15th. Last year, I planted several cucurbits in early August, and they just barely grew me mature fruit that I harvested just before our first frost on October 15th.

With overwintering cold weather crops, I’m starting to suspect “too late” is around mid September. They need to have time to get big enough to survive. Or so I suspect, based on the brassicas that I planted in early October all surviving frosts until December, but not growing at all, and then dying when gigantic piles of snow started flumping on them. They may have done better if I had put an unheated greenhouse on top of them, though. I suspect it wasn’t the cold, but rather the weight of the snow and the way it blocked sunlight, that kept killing my brassica seedlings.

As for eco-signs that may be helpful as reference to people in other places:

My daffodils have been flowering for about a week and a half. My echinecea seeds sprouted a month ago.
The peach trees in our neighborhood are starting to show little flower buds that haven’t opened up yet.

As for invasive weeds, the Siberian elms are starting to bud, the dandelions aren’t flowering yet, and the stars of Bethlehem are three times as tall as the grass, with no flowers yet. No signs of bindweed or purslane yet.

Hopefully those are all helpful references.

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@UnicornEmily It seems possible that it was the snow that killed your brassicas and not cold per se. They seem so weak for first weeks that they would be easily crushed. Maybe try sowing in autumn to have them a pit more mature. If your cold weather comes with protective layer of snow they should be able to take more than they normally can take.

That’s what I’m thinking, that it was probably the weight of the snow (maybe combined with no access to sunlight) that killed them. My brassicas with a plastic tupperware over top of them did great, and I think I sowed them at around the same time. Maybe it was having a degree or two of extra warmth that did it, but I highly doubt it. Those brassica stems sure look tiny and fragile, whereas peas and fava beans have much sturdier stems. I’m thinking that may make them better able to bear being buried in heavy snow.

(Sigh.) As for snow cover . . .

See, that’s the thing about my winters . . . there’s plenty of snow, but it often melts completely. This can be nice because it gets kinda warm in the daytime (maybe 40-50 degrees), and I suspect that will be really nice for winter crops that are adapted to it. There’s definitely no reliable snowcover for protection of perennials, though.

Lotsa freeze-thaw cycles! How exciting! :stuck_out_tongue_winking_eye:

I think it should be fine still. I’m thinking of british isles where they grow (or survive) trough winter and there they get regularly to -5 -7 C (around 20F) without significant snow cover. Snow cover during coldest periods should make enough difference to keep temperature at that range even if it’s much colder than that. Especially when you don’t get extended cold periods that would freeze the ground deep. So ground stays warm enough to give little heat to plants during cold spells. Lack of light shouldn’t be problem as it’s cold enough that plants don’t need that much light. My experience is that brassicas take atleast month to reach size where they produce crop of leaves or are big enough to start producing other crops for non leafy brassicas. It might be quite hard for them grow big enough to start producing crops timewise if they are sown late winter/early spring before heat hits. Or they get buried by late snow storm.

Okay, cool, so it was probably just the weight of the snow. I guess I’ll have to put some bitty brassica sprouts under hoop houses when my next winter starts, to test the idea and see! :wink:

For the record, 15 to 20 degrees F is zone 8b, which is really quite warm. :wink: I’m in zone 7b, with winter lows between 5-10 degrees F. Brassicas should be okay overwintering in 7b, though, so I think you’re right that it isn’t the cold.

Some of my brussels sprouts that I planted in April 2022 (they were nice and tall when the winter hit) got completely knocked flat onto the ground and don’t seem to be growing back now that warm weather’s hit, so I’m guessing the weight of the snow was a problem for them, too.

I seem to recall Mark Reed discovered that his broccolish that did the best job overwintering were shorter and squatter in shape. I wonder if snow weight is an issue for brassicas where he lives, too. Am I remembering that correctly, @MarkReed?

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I was bringing up british isles just to compare what those plants have to tolerate. Often under thick layer of snow temperature is at 0C or just couple degrees under. Not sure how much snow is needed for every C/F of temperature difference, but it doesn’t have to much to make significant difference in any case. Remember some years having water on top of lake ice under 15-20cm snow while it was -15 -20C for weeks before it finally froze. And there is no ground heat to give warmth on ice. That was quite fluffy snow that insulates best, but still I would expect any significant layer of snow to make quite a difference. Smaller plants probably best to overwinter under snow. They don’t have to be that big once spring weather arrives to produce fast.

Yes, that is correct, but it isn’t really a new discovery. Plants closer to the ground especially if there are some dry leaves or maybe some snow providing a little insulation and protection from freeze drying winds do better than larger plants. We rarely have snow anymore and winter is generally warmer than it used to be but for the last several years they have been punctuated with brief but extremely cold periods.

I believe that cold and very cold hardy plants are at severe risk in those conditions. They tend not to really even be dormant in long periods with barely a bit of frost and then BAM, -14 F for a couple of nights and they are toast. Cold hardy plants might be perfectly happy if it gradually got cold and stayed that way, especially if there was a bit of snow, but they can’t take the extreme and rapid change. Fortunately this past year, the very cold was accompanied with two or three inches of snow, the only snow we got all season.

I am very hesitant to make statements that imply anything typical about our weather anymore because.

I agree that is absolutely the case. Based on my observations, historical norms and phenology are completely worthless now. Even more recent data, say for just the last ten years is not a reliable indication of this year. USDA growing zones, and that Koppen Zone Classification are also of little value except in the most very general way.

Exceptions and extremes govern success or failure in my garden, not norms and averages and as Wojciech said these things become more extreme every year.

I’ve never actually measured soil temperature and I’m sure my dad who was born in 1913, nor did my grandfather who was born in 1882 did either. I learned what to plant and when to plant from them in the early 1960s and back then what they taught me worked just fine but it doesn’t work anymore. Yesterday it hit 81 degrees here and will likely do so again today and it’s starting to turn dry,

Its six weeks until our “last frost” date. Maybe it’s early spring or early summer and will stay this way and just get hotter and drier. Or maybe there will be another hard freeze or a couple of feet of wet snow, or maybe a combination, I can only guess.

My approach, whether it turns out to be an actual solution or not, is to select my crops for fast maturity and save a lot of seed so that I can go ahead and plant pretty much everything asap and start over if necessary.

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