Quote:
Originally Posted by bower
Some of my plants with purplish underside of leaves (and very purple stems) also had yellowish blotches on the older leaves. A feed of fish emulsion/molasses and a couple of days above 70 F, and those leaves are now all green - but there are still purple traces on the undersides. Mind you it is still around 40 F in the greenhouse every night, and we had one day that didn't crack 50 F when the greenhouse was snowcovered and dark... tough times, but they do seem to be hanging in there.
Since some of these plants already have 3 sets of true leaves, I've been wondering whether there is any reason to keep em in their pots any longer, instead of planting them into the big containers which will be their final home, in the same greenhouse. Any advice on that?
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This is a very old thread, but I was reading it and thought people might benefit from some information. Purple color to the leaves is almost always a phosphorus deficiency. This can be caused by a few factors. If you don't fertilize your plants properly, and many who area all organic can't as the sources of fertilizer and not 100% available to the plant right away.
Nitrogen is required by all plants, almost exclusively, when they are young. It modulates the uptake of almost all of the other nutrients. You could be feeding your plants a high phosphorus fertilizer and the purple won't be corrected on new leaves if there is not enough Nitrogen.
Purple color to the leaves usually won't go away as phosphorus is not normally transported into older leaves, only new growth. There must be a sufficient amount of phosphorus available as the plant grows in the plug tray or container. If you correct the fertility and new leaves are green and don't exhibit purplish tint then the problem is corrected.
We usually feed at 100 ppm Nitrogen and Potassium until the plants have their first true leaves. Then we do one feed per week of a fertilizer that has phosphorus at a rate of 30ppm. This phosphorus amount is continued until they are transplanted into the field 8-10 weeks later. Nitrogen and Potassium are upped to 150ppm per week once the plants are 6 weeks old.
Our fertilizer sources are:
Nitrogen: Calcium Nitrate, Potassium Nitrate
Phosphorus: 20-10-20 (Plant Marvel Complete or Millers Complete)
Potassium: Potassium Nitrate
We try to avoid Amonia and Urea Nitrogen sources as they cause a lot of stretch in tomatoes at early stages. It is hard enough to keep them short when in high density plug trays.
Knowing how much fertilizer to add to get to a particular PPM is easy math:
Desired PPM
--------------
% Nutrient x 75
This will give you the amount to add per US gallon of water. If mixing small amounts it is easier to use a 4 or five gallon bucket and a kitchen or postal scale for weights.
If you look at a fertilizer label you will see 20-10-20 or similar numbers. They are listed in order Nitrogen - Phosphorus - Potassium. Nitrogen is always 100 available. Phosphorus is not in a 100% plant usable form in the bag. You must divide the number by 2.3 to get the right amount. Potassium is also not 100% available, you must divide by 1.25. Always start with the nutrient that not available in other fertilizers. Usually this means phosphorus, then potassium and finally nitrogen.
Example:
Requirement: Fertilize tomatoes with 100 ppm of Nitrogen and Potassium, no Phosphorus. Your fertilizers are Calcium Nitrate (15.5-0-0 18% calcium) and Potassium Nitrate (13.75-0-48).
Calculations:
Potassium needed: 100ppm
48/1.25 = 38.5%
available potassium in Potassium Nitrate (13.75-0-48).
100
--------------- = .034 oz / gallon of water.
38.5 x 75
Nitrogen contributed by potassium nitrate would be:
13.75 x 75 x .034 = 35ppm
Nitrogen Needed: 100ppm
15.5% available nitrogen in Calcium Nitrate (15.5-0-0 18% Calcium)
100ppm - 35ppm = 65ppm (35ppm from Potassium Nitrate above)
65
------------ = .056 oz / gallon of water
15.5 x 75
Solution:
Add the following amounts per US gallon of water:
.034 oz Potassium Nitrate
.056 oz Calcium Nitrate
Using a 4 or five gallon bucket is highly suggested as the amount of fertilizer will be increased and easier to weigh.
Read some of the university trials and greenhouse grower information sheets. Almost all nutrient sources are listed in PPM of nutrient at a specific grow stage.
Organic inputs usually don't have a fixed amount of any particular nutrient so it is hard to know how much to add to your grow mix or soil. Some that do work are Fish Emulsion and Chilean Nitrate. I will warn you that fish emulsion STINKS. You will smell like a swabbie if you use it in your greenhouse routinely.
If you are fertilizing a LOT of plants a small chemical injector can be really handy. These devices suck a concentrated solution from a bucket and mix with water at a predetermined rate. I have a chemilizer that has a 1:100 dilution ratio. Meaning I mix the fertilizer concentrate 100 times stronger. Use the same calculations as about and then multiply by 100 to know how much to put in a bucket. The injector will draw a small amount out and mix with water as it flows through to get the desired rate.
This all seems like a lot, but I promise you it is easy. I made a simple sheet with my crops that lists growth stage (1-4) and fertilizer needs. I don't need to do any math and just mix up what I need, turn on the hose and water with the correct amount of fertilizer.
P.S.
Growth Stages are usually:
1: Radical emerges
2: Cotyledons emerge
3. Second Set of True leaves appear
4. Final stage until transplant/pot up.
Growth stages will vary with crop and as you gain experience, you will be able to make up your own sheets with your preferred inputs.
My hints:
- Fertilize with EVERY watering at a lower rate. If the weather turns cold and cloudy and you can't water for 3-5 days you want your plants to have enough nutrition to make it through v.s. needed to water to apply nutrients.
- Never use fertilizers with high amounts of Ammonical or Urea Nitrogen (Miracle Grow, Schultz's veggies, etc.). These are cheap sources of nitrogen and cause stretch in young plants and can burn at higher rates.
- ALWAYS do a quick sprinkle with clear water after fertilizing before the fertilizer solution has a chance to dry on the leaves. Some fertilizers, especially complete fertilizers, can burn foliage if left to dry on the leaves.
- Never use potting soil from the garden center to start seeds or young plants. These usually have polymers or large amounts of vermiculite in them to help retain water. This results in damping off from staying too wet or algae starts growing on the top of the cells. Use Professional Growing Mixes from Fafard, Premier Horticulture, SunGro, Berger, etc. These can usually be purchased at a local greenhouse or a greenhouse supply company (BFG, Carlin Sales, Nolt's Produce Supplies, etc.)
- DO NOT over water. Wait until the top of growing media is showing signs of drying out. Then water until it runs out the bottom of the tray. Spot check by lifting up a tray after you water so you know how heavy a flat is when it is properly wet. You will then be able to do a lift test to determine how dry or wet your flats are. This is very useful in the event you do have algae grow on the top of the media (Algae makes it look wet even when the grow media underneath is bone dry).