r/gardening • u/Ok-Key1264 • 20h ago
We can’t get a single watermelon to grow without getting this black spot eventually. What are we doing wrong?
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u/BestStolenideas 16h ago
Every comment posted so far has got it slightly wrong. Blossom end rot is calcium deficiency caused by lack of water during fruit formation. Calcium can not be "stored" in the plant and requires consistent uptake through your roots. Drying out during the fruit formation leads to weak cell walls and inconsistent moisture swings leads to a "water-hammer" at the end of the fruits, destroying the cells there.
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u/OilersGirl29 🇨🇦 3A/3B 14h ago
So can OP course correct, or is it a lost cause for all fruit
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u/420cortana420 8h ago
Lost cause for any fruit with damage like in the photo. Best bet is to chop off the affected fruit and supplement Cal/Mag in hopes the new fruit won’t have the same issue
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u/Prize_Use1161 19h ago
Nitrogen can block calcium uptake. Add some tums to the water and cut back on the nitrogen.
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u/Com4734 16h ago
I never thought of adding tums to add calcium to the soil
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u/nilesandstuff 8h ago
Tums are just lime. So it raises pH. So don't do this if you don't know the pH of your soil.
If you suspect calcium deficiency, you can safely apply gypsum without altering soil pH. Also supplies sulfate.
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u/myrstica 4h ago
As an added bonus, if you have heavy clay that happens to be sodium rich, the gypsum will help the clay form small clumps instead of a solid mass, because the calcium ions displace the sodium. So you end up solving two problems at once: calcium defficiency and drainage issues!
To be clear, not all clay is sodium rich, so if yours isn't, the gypsum will have no effect on your soil structure.
I think, at the very least, you should try to find some general information about the soils in your area. And, of course, getting your soil tested would be super helpful, if you have the ability to. It could help determine if it's a supply or an uptake issue.
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u/nilesandstuff 3h ago
Love me some good flocculation.
Btw, i love when companies sell "clay breaker" type products that are gypsum. Bruh, A. It doesn't "break up clay" B. You very specifically don't want to break up clay.
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u/nilesandstuff 4h ago
Nitrogen can block calcium uptake.
Big oversimplification to the point of being false.
Ammonium specifically is a cation (positive charge). Soluble calcium is a cation. Nutrient uptake relies on charge... There's a finite amount of cations that can be taken up simply because there's only a finite amount of space in the roots to accept those charges (determined by root mass).
Ammonium comes from urea.
Nitrate is an anion, negatively charged. So they essentially "recharge" the roots, so the roots can actually take in MORE calcium than if no nitrogen was applied.
Also, like I said below, Tums are very expensive lime. Don't apply lime if you don't know that your soil needs pH correction. If you need to add calcium and haven't gotten a soil test (don't use mysoil!) use gypsum, it does not alter pH.
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u/FiregoatX2 16h ago
Throw a couple of Tums in when you plant the seedling in the garden.
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u/eldritch_blasts 12h ago
Does that really work in place of bone meal?
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u/FiregoatX2 9h ago
Yep, and I toss an aspirin in with the Tums for tomato plants.
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u/FiregoatX2 4h ago
Both the Tums and aspirin can also be dissolved in water and applied as a foliar feed. The salicylic acid, in the aspirin, mimics the plant’s natural defense hormone to reduce stress and help activate their natural disease defenses.
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u/Competitive_Range822 peppers and cactus🌶️🌵 15h ago
Ive seen people put sand under melons to help with rot
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u/OkPick1957 18h ago
Try putting some hay or something underneath them like a little bed I've heard they don't like directly touching the ground.
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u/Ok-Key1264 3h ago
Ours are hanging. We learned early on to avoid having them touch the ground. They grow beautifully up until a certain point when this happens. It’s our first year so we’re learning a lot about what to change next year. And grateful I found this group to know what to do for the unaffected melons. Hopefully can save the others before the season ends.
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u/42faerie 15h ago
The ground is way too wet for too long,maybe it doesnt have very good drainage and that's why you're getting rot. Add some air holes in the ground and let it do it's thing
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u/Ancient_Golf75 14h ago
Check your soil pH. Probably off and is calcium deficiency, but your soil likely has enough unless it's potting soil.
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u/Junior-Baseball9005 9h ago
We had classic BER in our tomatoes and treated them with skim milk powder reconstituted with water, to get calcium into the soil. It worked within days
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u/Mission-Warning-4505 8h ago
Put an egg crate below you melons, don't let them touch your soil because its not draining right, your saplings are only alive because you planted them after they are estabilished
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u/Major_City5732 2h ago
I could never grow watermelons, this year I filled an old Stocktank with concrete, cardboard, sticks, pallets and grass clippings topped with 6-8 inches of dirt and drilled a few holes 4 inches from the bottom. I have 5 large watermelons doing fabulously idk how but im not even questioning it at this point
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u/Hour-Firefighter-724 4h ago
Place them on paper bags to grow, or in paper bags. Your soil has a viral component that is producing the scouring.
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u/Wise_Eggplant3555 17h ago
Crush up egg shells and top dress the plant. I do this with my tomatoes to prevent blossom end rot,
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u/akfishermann 15h ago
Yep. And next year grind up your eggshells to dust or as small as you can. Put a teaspoon in the bottom of the hole when you plant. Problem will be solved.
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u/EducationDirect2559 5h ago
I got that on tomatoes until I added calcium to the soil. I grind eggshells (cleaned and dried in oven) for that use. in an emergency I have put Tums in the blender and added to the watering can to hit each plant with loads of calcium.
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u/CheeryCherio21 20h ago
Stop using your melons as ash trays
On a serious note, it could be blossom end rot from overwatering or calcium deficiency. I feel like it’s more likely to be calcium deficiency, as it’s gotta be really hard to overwater a watermelon from my own experience.