Solutions to tomatoes not ripening?

We moved to northern Idaho (Zone 6a) four years ago and have been building garden beds from scratch. One odd behavior I’ve seen here is that my tomatoes will form fruits, grow to the appropriate size, then not finish ripening, sometimes sitting on the plants for over a month.

This last year I harvested over 100 lbs of tomatoes, most of them green. They ripened nicely in the garage but the flavor wasn’t great. They were bland. I planted several of my own seeds with known good flavor as well as some new varieties that do well in short-season areas. The plants themselves were healthy looking and so were the fruits. They just didn’t finish developing flavor and color.

Our summers are hot and dry even though the season is short (85-90 days or so). I’m currently looking into any nutrient deficiencies and/or heat-related issues that may be stressing the plants so that they don’t finish the job.

Has anyone else heard of this? Any suggestions are welcome.

Tomatoes normally take 6-9vk to ripen from flower and at full size around 3-4vk. From my experience it doesn’t depend much about temperature. Within same variety time has been around 10 day range between hotter and cooler year. It only slows down when days stay around +15C extended periods. Last year I noticed first time that one variety had a pause of 10-15 days between flowering and start of fruit development, but otherwise fruit ripened normally. That I think was due to extreme drought because it only happened in corner that drought was worst in. Your description sounds like they had not started to form early enough and therefore weren’t at technical ripeness (that is green fruit that ripens without any help from the plant). When they achieve technical ripeness they ripen just as well as vine ripened, although temperature difference might mean that you should wait week or two after the colour has changed as it might take more time than outdoors. I grow probably in a cooler climate than you and it needs to be really cool to slow down if varieties are atleast a bit used to cooler climates. Mostly delays come from transplant shock and/or hot/dry weather after planting. It also helps if transplants have been grown as close to their final conditions as possible. So good sunny place and exposore to some cool conditions helps getting them ready.

I grow in Zone 6a just a little further east in Western Montana.

Nitrogen matters. Too much delays fruit set. Though there the complaint is usually that the plant keeps growing and growing without setting fruit. I’ve talked to some folks who have overdone it with cheap/free/homemade horse manure and have that problem. If your garden soil is too rich put the tomatoes in pots with storebought potting soil for a year and raise sweet corn in the garden to deplete it a little.

Light matters, I grew Joseph Lofthouse’s R18 in 2021 with no problem out on my garden land but in 2022 I put it in a backyard garden bed and it barely made it to flowering by the time frost came. Other varieties were fine- but that backyard bed is too shaded by a maple tree we planted 15 years ago or so for R18- also I may have crowded it too much as it was a clump of R18. Also the maple has invaded the bed with its roots. Does your garden have enough light?

Varieties matter because of days to maturity from transplant often abbreviated DTM. What varieties are you using?

University of Idaho bred some Idaho specific varieties. Snake River Seeds carries them as does Glenn Drowns of Sandhill because he grew up in Northern Idaho.

Around here some varieties like Glacier and Stupice have been grown as standards for a long time. Triple Divide Seeds is a good source of varieties that do well in Western Montana.

The absolute earliest tomato I have found is Sweet Cherriette a small cherry tomato 35 DTM from transplant at eight weeks old.

Some other really early strains I’ve tried include: 42 Days, Forest Fire, Jagodka, and Anmore Dewdrop.

Early Determinates like Silvery Fir Tree bear their fruit in a single crop and thus don’t leave you with boxes of green tomatoes at the end of the season.

Though for me anything 75 DTM or less works pretty well. I tend to get about 100 frost free days and sometimes as many as 130 frost free days though.

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Thank you for the list of tomatoes. I always like to try new varieties, especially regional ones.

Excess nitrogen shouldn’t be an issue. The garden beds are made from logs, wood chips and soil from the property. The soil has no detectable nitrogen, phosphorus or potassium. I do amend for phosphorus but I’m trying to build up the life in the soil so I’m not adding a lot of amendments other than compost and kelp. The sun is good - to the point where we will have to put up shade cloth if we get another summer like two years ago.

The varieties I planted are:
Black Krim/cherry tomato cross: my seeds collected over 20 years, apx. 70 DTM
Early season mix from Montana Survival seed: 50-70 DTM. These produced huge amounts of tomatoes.
Floridade: Heat tolerant, 74 DTM
Green zebra: My seeds, 75 DTM.
New Yorker: Cold tolerant, 63 DTM.
Ropreco: My seeds, 65 DTM.

The thing that’s got me stumped is that the flavor was so bland in all of the varieties this year except for the black krim and it wasn’t as good as usual. The early season mix from Montana Survival seed grew well, produced early and prolifically, then just sat there. The Ropreco tends to not wait more than two weeks to start turning red once it’s at full size, but here it’s 4-6 weeks, then I have to harvest them because of frost. So it’s the combination of slow ripening and poor flavor that has me looking for nutrient deficiencies or microclimate issues. We do tend to get cold nights even when daytime is hot. That’s why I tried both a cold and heat tolerant variety. I’ve read that if tomatoes are stressed they will not put their energy into completing the ripening process.

On another note, I had great success with sweet peppers and chilis, which I didn’t expect because of the short season. So the soil seems to be suitable for nightshades.

How big were your transplants? Having a pause with production in my experience tells that your transplants were too big and that one early variety made fruit to flowers it had before/at transplanting, but then transplant shock made a pause in flowering (and thus fruiting) before it had established. Later varieties that probably weren’t as far in flowering it just delayed flowering. I have had best results with small transplants, about 6-7 weeks that were still sometime from flowering. Fastest varieties would have main flowering at the end of june and later varieties early to mid july. Fastest varieties would have 80-100% ripe by end of august and later usually about 50%, but all would be at technical ripeness. If your season tends to have cooler period before frosts that might slow down some, but it’s not something that is the main reason. With right transplants, good timing and right varieties there should be plenty of time to get ripe fruit. My season is around +10C at night and little over +20Cduring day at average. Usually rarely around/over +30 and often well below +20C as day max. Recently there has been some hotter and drier years and ripening has been faster in tomatoes compared to years with long cool periods

I’ve heard of blandness being in issue for people later in the season because of cold nights. What are your average summer night temps? I think the other thing that causes blandness is sufficient water (ie soil you think is too dry soil= tastier tomatoes that ripen earlier). I think people in prime tomato climates don’t have to worry about those things :slight_smile: – the heat and sun itself cause tomatoes to taste just fine.

I have major blandness issues because of cool day temps (58F is average summer high). I try to dry farm as much as possible to improve flavor, but then my problem is that blight loves humid and cool air temps and dry soil… so kind of a problem either way until I find the blight and drought tolerant, tasty promiscuous tomatoes of my dreams.

Other thought-- I intentionally gave up soil testing when I started landrace gardening, but I’m comfortable at reading soil tests. If you go that route feel free to post it here, it might be interesting in this case. Recommend Logan Labs.

I stop watering once fruit is formed.

My tomatoes get bland at the end of the season. If the first frost in early September doesn’t kill them, the short cold days and fall rain cause everything to split too.

My mom always greatly valued indeterminates and a huge pile of green tomatoes to ripen in boxes but those box-ripened greens never taste as good.

75 DTM is early enough for me, but you have a shorter season by about 10 to 15 days as a bad year here is 100 days. Still 65 DTM should have worked. I guess you could try putting in a Sweet Cherriette 35 DTM, a 42 Days 42 DTM, a Stupice 50 DTM, and a Silvery fir tree at 60 DTM and see if days to maturity from transplant matters much.

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Thanks for all the great responses.

Plant size at transplanting: My usual (last 30+ years) is 8-16 inches or so. They are hardened for weeks outside prior to transplanting. They didn’t have a delay in blossoming. Just ripening of the full sized fruit.

Cool night time temperatures is a likely contributor.
June: high 30s - high 50s, ave. high 40F
July/Aug: mid 40s - high 50s, ave. low 50F
We start getting frost damage on sensitive plants in late August even though the air temperature is in the high 30F range. We live in a valley that’s known to be colder than the surrounding area. Lots of little microclimates in north Idaho.

Overwatering is also a likely contributor, especially for the blandness issue. Thank you for this reminder. I came from Denver and we had to water like crazy due to the heat, low humidity and intense sunlight. We’ve had high daytime temps here but not the other factors, so I’ll back off on the watering after fruit set and see if things improve.

I think your transplants are too big not to have any delay because of transplant shock. It might not look like you have had transplant shock, but if you dont have anything to compare with it’s hard to know. Short season doesn’t allow even for small delays. I use transplants that are mostly 4-6 inches and max 8 for some bigger varieties, although next season I delay sowing so that they aren’t even that big. Those night time temps are about same as here. I haven’t seen night time temps having much if any effect, but low day temps do. Not before 15C if night are around 10C. It might be that your varieties just aren’t best suited for that climate and that variety that had pause just had transplant shock, but otherwise might do fine. I have mostly selected Russian, eastern europian or otherwise short season varieties. With being selective most (from about 50 varieties) have atleast started to ripen before end of august, but quite a few early enough to have most ripe before season end. Be selective and try as many as you can.

This page has some interesting points on flavor.

And I learned a new word, ‘thigmotropy’

“Thigmatropy is the name for an effect where plants alter their growth habits as a result of being touched.”

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Darrel Jones is a very interesting tomato expert! is his website. He has done some interesting frost and cold tolerance work.


Six week old tomatoes seem just right, to me, for transplanting into the field. They are big enough to outgrow the flea beetles, and small enough to minimize transplant shock.