Hi Karen! Thanks for your question.

Yellowing leaves can be caused by several things – either they are not receiving enough water, or receiving too much water, or not receiving enough sunlight.

Another common problem when dealing with seedlings is not hardening them off. When starting seeds indoors, the seedlings get used to the light they are receiving inside (whether it’s from a window or artificial lighting). Once they are taken outdoors, they aren’t used to the powerful sun and it may burn them if left out too long. You can get them ready for their permanent home outdoors by slowly hardening them off. This means you set them outdoors a little at a time, increasing the amount of exposure slowly.

At first, you set them out for an hour a day over the course of a week. The next week you set them out for two hours. You continually increase the amount of time they are out until they are outside for the entire day. This gives the seedling time to adjust to the harsh sun and wind.

If hardening off isn’t the case, then I would make sure they are getting enough light (if artificial light is used they need about 12-14 hours of light). Also check how much you are watering them. Do not allow the soil in the pots to dry out. You don’t want it soggy, but consistently moist.

If that doesn’t help then I would give the seedlings a feeding of diluted fish emulsion once a day for several days. This will give them a helpful shot of nutrients.

I hope this helps, Karen, and please come back if you have any other questions.

I started all my tomatoes from seed this year, they got their 3rd set of leaves so I transfered them out of the jiffy seed starter tray into small pots, the ones you can just plant into the ground when you put your tomatoes outside for the summer, they are turning yellow, whats up?

Hi Mr Blain,

Yellowing leaves can be due to a number of different situations. It can be caused by over watering or under watering. A quick and easy way to check your watering levels is by checking the moisture in the soil. The easiest way is to stick your finger in the soil about an inch or two deep. If the soil feels dry to the touch water the plants. If the soil feels moist wait until the next day and check it again. Water the plants once the soil feels dry again. This is a very scientific approach, but it is a good cursory check.

Not enough nitrogen in the soil can also cause yellowing leaves. Even when purchasing commercial soils it is still a good idea to check the nutrient availability of that soil to make sure it offers what the plants need. If there are low amounts of nitrogen in the soil it is good to add a little, but do not go overboard with nitrogen as too much can cause other problems.

Also check for pests like aphids, leaf hoppers, or spider mites as they can cause yellowing in some cases.

As for curling leaves, this can be quite common during hot, dry conditions but does not affect the growth and production of the plant in most cases.

I hope this helps to answer your questions!

Hi Mr Riddle
This is the first time we have had a glass house. We have used tomato soil which came in bags so it should have the correct amount of goodies. However, some of the plants leaves have curled under and one plant is going quite yellow all over. Hmmm. We have drippers which come on twice a day but maybe they aren’t getting enough water? Or maybe the yellow one isn’t? It has been very hot over the last week so perhaps the curly ones may be a little stressed? Our courgettes are producing manificently and all our seedlings are doing fine. Any help would be great. Many thanks
Glenys

Hi Tony – Do you mean measuring the nitrogen in your soil? If so, you will need to purchase a soil test kit. They are pretty inexpensive and you can find that at Lowe’s or Home Depot. It will give you a good idea of the nitrogen content of your soil.

If you are talking about the nitrogen in fertilizers, then you will want to check the N-P-K- numbers on the fertilizer container. All fertilizers must have the N-P-K numbers labeled on the container somewhere. The N-P-K is a series of three numbers that tell you what percentage of each nutrient the fertilizer contains. For instance, if the fertilizer has 3-4-5 on the bag then it has 3% nitrogen(N), 4% phosphorus(P), and 5% potassium(K).

3-4-5 is a good nutrient rating for tomatoes. You don’t want to use a high percentage of nitrogen with tomatoes because it could cause nice, lush plants but little fruit. You just want to give it enough for healthy foliage. A low number of N, like 3, is a good level to use.

I hope this answers your question.

i’m new to growing so how do you measure for nitrogen and how is it purshased?

Hi Joyce – If the leaves on the bottom branches of the plant are curling it is probably just a sign of stress. Most of the time this is not detrimental to the production of the plants. It doesn’t look all that great, but the plant should still produce just fine.

If the curled leaves have purple coloration in the veins of the leaf, it could be a sign of curly top virus. More than likely, your are just stress.

You may want to feed your plants once or twice a week with fish emulsion. Mix two capfuls of fish emulsion to every one gallon of water, and feed the plants with the mixture. This will supply some very good nutrients to the plant which should perk them up. If the yellowing is bad, give the plants some every day for 10 – 14 days.

Hi Mr Riddle this is my first year growing tomatoes, they are in pots on my balcony, the leaves are curling under and yellowing I don’t know how to treat this problem. I do water every 2 to 3 days. there are tomatoes growing on one however it looks really bad.

Hello

Epsom salt is magnesium sulfate and supplies magnesium, phosphate and some other traces of calcium, among other elements. It can help with blossom end rot and other conditions. Epsom salt should be used only if needed because it can cause high concentrations of magnesium in the soil if used too much.

What is the purpose of using epson salts in gardens? I remember using it years ago for yellowing leaves but what does it supply to the plant? Is it nitrogen, iron, neither?

container gardener