Heirloom Tomatoes Not Ripening

Advice from the Help Desk of the UC Master Gardener Program of Contra Costa County

Client's Request: I purchased a Yellow Rainbow Beefsteak Tomato Plant at your annual sale in Walnut Creek this year. The plant has grown quite big and has about four tomatoes on the plant. They have stayed about the same size for about two weeks now and are not turning yellow — they are green. I have used organic tomato fertilizer, but it has not helped. Any suggestions?

MGCC Help Desk Response: Thank you for contacting our UC Master Gardener Program Help Desk about the slow production rate of your Yellow Rainbow Beefsteak Tomato plant. First off, thanks for supporting our Program by purchasing tomato plants at our annual plant sale; it's a primary source of the income that funds our Help Desk and other public outreach programs.

It's hard to know why your tomato has been so slow to produce ripe tomatoes. However, Yellow Rainbow Beefsteak tomatoes are one of the slower tomatoes to start producing—some websites call them “fall producers”. The typical time for the plants to start producing is about 90 days from the time the seedlings go into the ground, so it does seem that your plant is a bit late. One possibility is that the soil where it is planted had excessive nitrogen fertilizer. When there is excess nitrogen, tomato plants often produce abundant foliage but set very few tomatoes. Next year, you might want to do a soil test before you plant your tomatoes. You can purchase an inexpensive home soils test kit at a nursery or big box store. The kit typically allows you to test levels of three principal nutrients—nitrogen, phosphorous and potassium (N, P, K). N is used by plants to produce green foliage; P helps with fruit production and K helps with roots and the overall well-being of the plant. Then use fertilizers only as needed to address any nutrient deficits.

You indicated that you used an organic tomato fertilizer. That likely included some amount of all three nutrients (and possibly other micro-nutrients such as calcium). If the plant was already growing well, it probably didn't need more nitrogen. Applying a fertilizer that added only phosphorous might have done the job. Also, you didn't say when you applied the fertilizer, but we are guessing you might have added it to help spur fruit production. If you applied it before the four tomatoes set, the fact that you now have those tomatoes on the plant may be a sign that the fertilizer application did help. As for the slow growth of the size of the tomatoes and their being slow to ripen, I think you just need to be patient. If is not uncommon for heirloom tomatoes to take several weeks to mature. I waited about six weeks after fruit set for tomatoes on one of my plants this year to finally grow to an appropriate size and ripen.

Tomatoes don't need to have insect pollinators to set fruit. Rather, the flowers are typically pollinated by wind action. If you have flowers on your plant that have not yet set fruit, try to duplicate the wind effect by gently shaking the plants once or twice a day, preferably mid-morning. Also, it may be helpful for you to know that tomatoes usually don't set fruit when daytime temperatures are more than 85 to 90 degrees. It's been somewhat cooler throughout our county in recent days (but not the last several days when this was edited and updated for posting) and hopefully, you may have had some additional fruit set then. But it's about to get hotter again for the next several days (or more likely cool again thank goodness). By early week when this blog is posted, it's supposed to be cooler again. Hopefully, at that time some additional tomatoes will set, particularly if you remember to shake the plant occasionally.

One final thought, keep track of how well all of your tomato plants produce and how much you enjoy their flavor. I typically try to plant at least one variety that has been a reliable producer in prior years to make it more likely that I'll get a steady supply of tomatoes. I re-plant slow producing varieties again only if I really thought their taste was outstanding and worth the wait and low production rate.

Hope you soon have some tasty tomatoes to harvest.

Help Desk of the UC Master Gardener Program of Contra Costa County (tkl)

Notes: Contra Costa MG's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at ht tp://ccmg.edu/HortCoCo/ You can also subscribe to the Blog.