📌 Quick Summary: Fixing Purple Tomato Leaves
- 💜 The Purple Warning: If your newly transplanted tomato seedlings start turning purple or dark blue on the leaves and stems, it is almost always Phosphorus Lockout caused by cold soil.
- 🥶 How it Works: The soil probably has plenty of Phosphorus in it, but tomato roots physically cannot absorb it when the soil temperature drops below 55°F (13°C).
- 🩹 The Temporary Fix: Adding granular fertilizer to the dirt won’t help if the roots are freezing! You must apply a liquid Phosphorus fertilizer as a foliar spray directly to the leaves, and cover the plants with a frost blanket to trap heat.
- 🧶 Trellis Timing: Never tie your tomatoes permanently to their tall vertical strings immediately after spring transplanting. Tie them to short stakes first so you can still throw protective frost blankets over them if a cold snap hits!
If you don’t mind me chiming in! 🙋♀️This exact picture happens when the soil is too cold. The root system stops working entirely and is likely starting to die off. This causes a massive imbalance of all nutrients inside the plant.
We are expecting warmer weather in the next few days. Once it warms up, you can rehabilitate them, but you must only feed them with chelated fertilizers applied as a **foliar spray** (directly on the leaves).
Galina, you also need to cover them with spunbond (frost blankets) for the next 1-2 weeks. What is that sprinkled on top of the root zone in the picture? And are you using a space heater to warm the air?
Raduga (Galina) wrote:
Galina ,you also need to cover them from the sun with spunbond…
Galya, what sun?! It’s completely overcast and freezing. The soil seems okay, but it’s probably very cold. Should I dig them up and put them back into pots? I noticed the exact same symptoms on the seedlings that are still sitting unplanted in their cups in my other greenhouse.
Ludmila, I can only measure the soil temperature with my hand. The air temperature in the greenhouse is 50°F (10°C). I bought a cheap soil thermometer, but it doesn’t work. I try to turn on the space heater at night.
Right now it is 35°F (+2°C) and raining outside, and 50°F (+10°C) inside the greenhouse. I just went out and took pictures of the other bushes.
gala7496 (Galina) wrote:
Galya, what sun?!
Galochka, please don’t get offended or upset! 🌻
We are practically neighbors—you are in the Priozersky district and I’m in the Vyborgsky district, roughly the same distance from the city. I know exactly what the weather is doing right now!
When I said to cover them from the sun, I meant the sun that will eventually peek through the clouds when this storm passes.
I’m actually right on the border of those two districts! Now I guess all we can do is hope for future sunshine.Though Bill Gates is currently trying to implement a global initiative to block out the sun for 3 years by spraying special powders into the atmosphere. Maybe he’s already rolling out his idea over us! We have absolutely zero sun, it is overcast and colder than I’ve ever seen it.
Galina, I only chimed in because I’ve stepped on this exact same rake before! 😂When the soil is freezing cold, the plant first fails to absorb Phosphorus (which causes the purple colors). But eventually, it leads to a complete breakdown in the uptake of all other elements. The leaves will start developing yellow spots and will begin to die off completely.
But honestly, this is just standard St. Petersburg weather. It’s not a rare occurrence at all. The real question is: what do we do about it right now? It would be really good to know your exact soil temperature. Do you have any kind of outdoor or pool thermometer you could stick in the dirt?
Raduga (Galina) wrote:
The real question is: what do we do about it right now?
At the very least, I would untie them from their tall vertical strings, tie them to short wooden stakes instead, put up wire hoops (preferably double hoops, with one set higher than the other), and cover them with heavy frost blanket (spunbond/agribon).
I never tie my tomatoes permanently to their final trellis strings in May. I almost always end up needing to cover them with blankets again!
Raduga (Galina) wrote:
It would be really good to know your exact soil temperature.
Why? They are already planted. What difference does the temperature make now?
natko (Natalia) wrote:
Why? They are already planted.
Well, Galina was asking earlier if she should physically dig them back up and put them back in pots! That’s why I asked. 🤷♀️
Covering them doesn’t really help much. My seedlings sat out on the balcony for over a month, surviving temperatures around 39-42°F (+4-6°C) without any extra attention. I planted them in the greenhouse three days ago, and I can already see Phosphorus deficiency showing up!In just 3 days! The row covers don’t help at all because the soil temperature underneath them is basically exactly the same as the rest of the greenhouse, maybe just 1 degree warmer.
gala7496 (Galina) wrote:
…cold weather, like never before.
I am always surprised when people say “like never before.” It is literally like this every single year at this time! I had a hailstorm completely destroy my greenhouse right at the beginning of May a few years ago.
For a variety of reasons, I’ve started moving out to the summer house at the end of May for the past two years. Obviously, my onions suffer from the late planting, but for every other plant, it is absolutely wonderful. There is zero transplant stress. No burnt or purple leaves. I plant them directly into warm, comfortable soil.
Galya, is it possible this is a reaction to that Trichoderma you mentioned earlier? My plants look slightly different when they suffer from cold. Or maybe it’s just the color distortion in the photo.
Tatunya (Tanya) wrote:
The row covers don’t help at all…
They help me tremendously. I planted mine in the greenhouse on April 17th, with zero supplemental heating. The only one turning blue is ‘Sgt. Pepper’s’, which is exactly what that variety is supposed to do. The rest of my seedlings are sitting in my other greenhouse under heavy frost blankets. They are totally green and problem-free.
My neighbor’s seedlings, which she was supposed to pick up two weeks ago, are just sitting totally uncovered in crates in the middle of my greenhouse, and even they are growing fine!
natko (Natalia) wrote:
I never tie my tomatoes permanently to their final trellis strings in May.
I’ll post a picture tomorrow to show you exactly how I set mine up, maybe some of you will want to adopt my method. I completely agree: I only hang the main vertical trellis strings once I am 100% sure the threat of returning frost has passed!
Edit (Next day):
Here is the photo. A promise is a promise!
👨🔬 Editor’s Botanical Note: Phosphorus Lockout
If you plant tomatoes early in the spring and the leaves suddenly turn purple, do not panic and do not dump granular fertilizer into the soil! This is called Phosphorus Lockout.
Tomato roots are physically unable to absorb Phosphorus when the soil temperature drops below 55°F (13°C). The Phosphorus is sitting right there in the dirt, but the freezing roots can’t eat it. If you add more fertilizer to the soil, you risk burning the roots with salt buildup when the weather finally warms up.
The Fix: Raduga (Galina) gives the perfect professional advice here. You must apply a liquid Phosphorus fertilizer as a Foliar Spray. By spraying a diluted, water-soluble fertilizer (or compost tea) directly onto the leaves, the plant absorbs the nutrients through its stomata, completely bypassing the freezing root system until the soil warms up!
