Hi there!
The lower leaves of my tomato plants are turning purple, start to curl and dry up. On the stems I see little black spots...Is this potassium or phospor deficiency? I use compost mixed with a small amount of horse manure and wood ashes, so I don't see how there could be a deficiency. My other plants (Melons, Peppers, Eggplants and Ocra's) don't have these problems and are growing really well... They are also given enough water.
i would actually stop using the wood ash, personally. It may be good for some plants, but it does raise the soil PH to a level most plants cant stand if too much is applied, or if it is applied too often. You can keep using the horse manure, but the wood ash for soil is like sugar is to us--best used sparingly.
And actually, once your soil becomes too alkaline from all the wood ashes, you are actually doing the opposite to the soil of what you think you may be doing, because a high PH level will actually lock out phosphorus and potassium, and also manganese from the plants, and they wont be able to take it in.
I would do a soil test before adding anything else in, you would want your soil PH to be somewhere within 6 - 7 for most plants.
Yes purple leaves usually mean phosphorus deficiency. I understand that wood ash isn't a good idea for plants that prefer more acid soil, which tomato do, maybe check your soil pH and lower it with peat moss.
This message was edited May 30, 2015 9:23 PM
Thank you for your replies!
As the tomatoe plants are already in the ground, is there anything I can do now to lower the ph? It's difficult to add peat moss without damaging the roots... Or could I give my plants phospurus in any other way, by using a fertilizer with P and ammonium sulphate for instance?
This message was edited May 31, 2015 4:54 AM
This message was edited May 31, 2015 5:54 AM
I would test the soil first to make sure that's the problem. Purple leaves can also mean they were exposed to cold temps. You can add P by using a fertilizer with a high middle #. I have very alkaline soil and water ( on a well) but I've never had a problem growing anything except certain plants like Blueberries and Azaelas (sp?) that require an acidic soil.
If you are adding the wood ash as a source of phosphorus in very small doses, OK.
If you are adding it to keep the pH up a bit in the compost pile which is very high in organic matter, OK.
In either of these uses a little bit goes a LONG way.
How to lower the pH in soil where something is already growing:
Mulch with lots of very fine organic matter such as peat moss. It will work its way down through the soil over time, and each time you water it will release organic acids that will get watered into the root zone.
Next season, add a lot more organic matter, (compost, manure, other) to the soil.
Kvan, in your first post you mentioned black spots on the stems. From my experience that is due to fungus or bacteria....are there more spots or are they bigger? I could very well be wrong but it is a thought.
Yes there are really tiny black spots on those tomato plants that have the most purple, curled leaves. They don't get bigger, but they multiply. It starts from the bottom and goes up at the same pace the leaves curl/get purple (from bottom to top). I don't find anything on the internet that explains this... I assume it's a different symptom of phosphorus deficiency?
Anyway, I tested the soil with some ph strips. The ph is 7 (or slightly more), the rainwater I use has a ph of 5.
I mixed some peat moss in the top layer of each pot (I use 10 liter pots to grow my tomatoes in) and I added a bit of fertilizer to my water.
I really hope the plants will get better...
This message was edited Jun 1, 2015 11:11 AM
pH of the soil pretty close to neutral is good. Maximum availability of most nutrients is when the soil is not too far from neutral.
Rain water with a pH of 5 is not a big problem.
Pure water falling through the air picks up carbon dioxide. This reacts with the water and forms an acid. (Carbonic acid) With no other minerals in the water the CO2 dictates the pH. It takes very little CO2 to make the pH of pure water (rain water) drop way into the acidic range.
If you do not want the pH to be so low then add a very small amount of potassium bicarbonate. Start with 1 teaspoon per 50 gallons and stir it around to be sure it is well distributed. Then test the pH. If it takes another teaspoon or so per 50 gallons to stabilize the pH closer to neutral this is not a lot. Potassium bicarbonate is a source of potassium (though at this low dosage it almost doesn't count as a source of K) and bicarbonate ions. The bicarbonate interacts with the acid formed when the CO2 entered the rain water, neutralizing it. Beneficial microorganisms in the soil can use the bicarbonates, so it is just fine to add them to the water, then the soil in this small amount.
It seems the fertilizer does its job...the purple color is fading away:-). It's very strange, the tomatoes that I planted outside didn't get any wood ashes and are getting the same problem. So the problem lies with the compost...
I buy this compost from the local waste manegement company, it's made from all garden waste from citizens in the neighborhood.
If it's just low in Phosphorus that can be added, as you now know. What are the temps in your area?
Past month temperatures were rather low, 13C° on average. In my greenhouse it was mostly 20C° during the day. How does temperature affect phosphorus withdrawal?
Tomatoes are warm weather plants, if the temps are too low it can inhibit the plant's ability to uptake P. From what I've read the lowest temp for tomato plants is about 50* F. If your temps have been consistently lower then that, your soil may have enough P but the plants just can't use it. This is more common in young plants and will pass when the temps warm up. How talk are your plants?
My plants are 1m in height now...So I guess it will get better when they grow a little more.
Your plants arent seedlings then. Lol It wouldn't hurt to add a fertilizer with high P but I think when the temps warm up that will help too.
One more question. Are your plants blooming or setting fruit?
Compost is not fertilizer.
Fertilizer is not compost.
When the soil needs to have organic matter added you buy lots of compost and use it generously. It improves the soil structure, chemistry and microorganism population.
When the soil needs the specific elements that plants need to grow you buy fertilizer and add it in small amounts, carefully planned to meet the needs of the plants you are growing, in the soil you have.
These are 2 separate concepts that have gotten muddled by the concepts of 'organic' and 'natural' and so on.
When you are growing a crop whether it is vegetables or lawn grasses you are growing plants in a way that is not natural. You are growing them in an intense planting layout, and are expecting extraordinary growth. More than what happens in nature.
You need to treat the soil accordingly:
Add compost to make it loose, open, easy for roots to grow through. Compost will also improve the soil in many other ways, such as lowering the pH, but it simply does not have all the elements plants need in the ratios they need, available at the rate they need.
Add fertilizer to supply the nutrients the plants need. There are organic fertilizers, if that is the way you want to go, but blood meal, bone meal, cottonseed meal, greensand, and many other materials are added in small amounts, and do not affect the soil chemistry like compost does.
Fertilizer is the source of nitrogen, phosphorus, potassium and all the secondary and micro nutrients plants need. While these may be present in compost, they are locked up in a way that plants cannot get them.
