E-mail - Yellow/Dry Leaves with Spots

Dr. Myers

I have a problem, my plants have leaves that are yellowing from the bottom with tiny spots; the lowest leaves have started to dry up and brown. Can you help?

Hello,  Thanks for your question.  Yellow leaves can be due to a lot of things, but the fact that you told me you have little spots (speckling) leads me to think you have an infestation of some sort. Also, the brown and dry leaves are often a symptom of an infestation. The pests are sucking the juice out of the plant leaves. When it gets bad enough your leaves can brown and dry out. The little dots you see are where individual insects have sucked a meal of plant juice.
You should look and see if there is any webbing between the leaves, if so you have spider mites. Look closely, if you have a magnifying lens you can look for small crawly things. You could also have aphids. I have written about both on the blog, please click on the linked words and read my suggestions about how to deal with this problem. There are a lot of products sold by HTGSupply.com, but none are an easy solution. Oftentimes I suggest finishing up your plants then cleaning the room with a 10% bleach or hydrogen peroxide solution. If your grow area is open to the outside, you may want to change this or you may have a recurring problem every time you grow.

Good Growing,
Dr. E. R. Myers


E- mail - Brown or Scorched Leaf Tips

Hey Doc,
My plants have begun to have brown leaf tips, do you know what causes this or more importantly how to stop it. Will this get worse and how will it affect yield? Thanks.

Thanks for your question, it is one a lot of growers might have.  Low humidity is usually the first cause of brown leaf tips when growing indoors under a HPS or MH. You can mist your plants each day, but that might risk fungal infestation if you are growing plants that are susceptible to fungus. If you are going to mist your plants do so at the beginning of the lights on cycle. You could also have the plants sit in a tray with some stones in it and keep water in the tray. You don’t want your pots to sit in standing water, so the stones keep the pot up out of the water and the water then evaporates and increases the humidity. If this is the cause, it is not a big problem and if it does not get worse I would say you don’t really need to do anything. This should not affect your yield.
My next thought would be how you water the plants. Poor root health from overwatering or excessive soil dryness (especially between watering) can cause a plant to have brown root tips. My next suggestion would be to look at your water and how you apply your fertilizer. Some specific nutrient toxicities (such as fluoride, copper or boron can show up as brown leaf tips. If your water has fluoride in it you may want to buy water or get a water filter from HTGSupply.com. Keep in mind You do not need to buy or filter ALL your water, most substances have a threshold where they become toxic. In other words if you use less water with fluoride etc. you should notice the new leaf tips are not brown. I am not sure if the leaf tips that have the brown tips will recover (turn green again) so what you want to look for to see if you have fixed your problem is that new leaves do not have brown tips.
Last, if you are using a pesticide that can also cause brown leaf tips. Let me know if you have any other questions.
Good Growing
Dr. E.R. Myers


Plant Measurements to Compare Plant Growth

I have written posts about how to test plant growth scientifically.  I am finishing up my next post comparing a group of plants that had AUROA’s ROOTS beneficial microorganisms added to a second group that had everything the same accept no added beneficial organisms. Below is a list of potential ways you can compare plants growth.
You can compare seed germination by simply comparing the percentage of seeds that germinate in each group
You can compare the number of days from planting to emergence when plants develop cotyledons (the first leaves you see after germination).
I compared plant height by measuring the plants every 2-4 days. You measure from the medium the plants are growing in to the top of the plant stem.
You can also compare the number and size of leaves. Leaf size is a good indicator of plant health. You should also include observations about the leaf tips (brown or yellow). You could place the leaves over graph paper and trace them You can then determine and compare the surface area of the leaves. If you use the same type of paper, you can cut out the leaves and weigh them to compare the estimated mass of the leaves.
Plant color is another good indicator of plant health and you could compare this. You should not try to compare shades of green but rather note if there are specific color differences like yellow or brown spots or tips.
If you are growing plants that flower there are two easy ways to compare flowering on plants. First, you can compare the time to flowering. You can do this by comparing how long from the initial planting until the plants begin to flower. If you adjust the light cycle to induce flowering, you can compare the first flowering from when you change the light cycle.
The second way to compare flowering is to record the number of flowers. You can count every flower if weigh all the flowers
Good Growing
Dr. E.R. Myers


Speed up flowering - Revisited.

I have written about speeding up germination and about speeding up vegetative growth And speeding up flowering and I want to add to how to speed up flowering thanks to a scientific experiment (LINK) done by my friend. Basically, the cooler you have the night temperatures the faster the flowering response will be.
My friend just had a second child, and his grow closet is now his youngest kids closet. He moved his grow lights into his garage. The garage is attached to the house, but is not heated and it is only about 10 degrees above outside temperatures, and it is on the south side of the home so it gets very hot on sunny days. He can no longer grow over the winter months, or in the middle of summer. He started the seeds inside his house under a fluorescent light then after a few weeks he put the plants in the garage under an HPS. One thing he did was he switched his light and dark cycle, so that the lights are on (and making heat) at night when it is cooler outside/in the garage. He is growing in a grow tent to prevent light from affecting flowering. This also helps insulate the plants from the more extreme temperatures in the garage.
He keeps good notes on flowering time and he has data showing that since his plants are growing in the garage flowering occurs 4 days earlier with colder night temperatures. When the lights are off he frequently has temperatures in the 40’s and even in the upper 30’s one time. This would kill basil and some other sensitive herbs, but will cause most plants to have a faster flowering response. Especially plants that flower in the fall/ with 12 hours of darkness. These plants will ‘think’ fall is coming so they better get flowering and reproduce.
I don’t recommend growing in an unheated garage to speed up flowering, but you could consider keeping the vent fan running even during the dark cycle when you begin flowering to lower the night temperatures as much as possible. Even if you can’t get the temperatures into the 40’s the greater the difference between the high of the day and the night temperature the faster you will see a flower response.
Good Growing
Dr. E.R. Myers