E-Mail Ques. Mother Plant -- Blue vs.Red Light T5HO

Howdy Doc;
I just got a new tent from HTGSupply.com. 48x24-48. I'm using a T-5 light. I have 2 blue & red blubs. It worked great before I got the tent. Now should I use 4 blue/WHITE in the tent…? I am going to use this as a mother’s tent for clones. Thanks for your time.
p.s. The last Q worked out well..

--You should use all blue/white, since that light will promote vegetative growth. I don't think the mixture of red and blue will be BAD for the mother or clones, but blue light does promote vegetative growth, and short internode lengths. So, my advice is use the blue bulbs over the red.

If you are looking to make a lot of clones you could keep one or two mothers in a tent and set up a clone shelf like I will describe in Aug 2009.

Good Growing
Dr. E. R. Myers


E-mail Ques. Determining seed sex

Doctor Myers,
My question is when is a seeds sex determined? Is it genetically predetermined when
the seed is created, or do environmental factors play a part? Thank you
and htg supply for some really interesting and well written articles
and hopefully the answer to my question-

A. This is a great question but there is no one definitive scientific answer (good question!). Your question of course suggests you are growing a dioecious plant species, one that has separate male and female plants. Most plants have both male and female flowers on the same plant. Many plants seem to have a predetermined sex at fertilization, (This means seed sex is determined at germination for many plants) but this is not always the case. Most scientists think that having separate male and female plants has evolved several times in flowering plants. This means there may be differences in how sex is determined in a seed.
To give you more of a helpful answer, there is some specific research on the subject of sex determination. It was found that the amount of fertilizing pollen can influence the sex ratio (number of males vs. females) in dioecious plants. It was found an increase in pollen amount leads to decrease in number of male plants in the progeny. This relationship was confirmed on three plant species from three families – Rumex acetosa (Polygonaceae), Melandrium album (Cariophyllaceae), and Humulus japonicus (Cannabinaceae). If you are interested in female plants, you should then use a lot of pollen when breeding. This idea of more females occurring when there is a lot of pollen during fertilization is logical evolutionarily too. If there is a lot of pollen it means there is a lot of males in the population. Therefore, it would be better to have female offspring since having a male offspring would mean it had to compete with a lot of other males. Plants that had this genetic trait (making females when there is a lot of pollen produced by males) would be successful since all their daughters would be pollinated and would pass on their genes, the mechanism of natural selection.
Other factors like temperature, light and water may have an effect on the number of males and females that come from a group seeds, however this is going to be different from one species to the next. The truth is there is a lot to learn in this area of plant growing and your question is right on the edge of scientific unerstanding. Thanks for your question!

Good Growing,
Dr. E. R Myers


Some things to add to any grow medium - tricks of the trade

As a soil grower, one of my favorite mixes is three parts top soil 1 part vermiculate 1 part perlite 1 part sand. It is what I use in my greenhouse. I have been adding part coir to the mix starting last semester which will cause the soil to hold more water. Basically, you can adjust your soil to your plants or your watering habits -- adding more sand and perlite will increase drainage while coir vermiculite and soil will increase some water retention. You could also try adding screened compost to any mix (Compost article) this will improve water retention and aeration as well as supply most nutrients including micro nutrients. Experimentation will lead you to find the best medium for your plant and your growing environment, one size does not fit all. I used to like to sit in front of my plants each day for awhile, and I would water them a bit each day. For this I made a mixture with a lot of drainage. Now, I am busy and I don’t even look at the plants each day sometimes, so I have more vermiculite and coir so that I know the plants won’t dry out.
One thing you could try no matter what you grow is adding Epsom salts, one tea spoon per gallon which will supply Mg and sulfur. Also, know that if you use time release fertilizers they are usually meant for outside use and their breakdown (release) is based on temperature. In other words, indoor growers will have higher temperatures and faster breakdown. First, know this means you will get a higher amount of fertilizer and second, the fertilizers will not last as long. If you want the fertilizer to be in the medium for 6 months, you should get 9 month release. Since the release is quicker, be conservative in how much time release fertilizer you use.
I hope this month’s articles on mediums help you to build a better medium for your plants. As always, I encourage you to experiment and find the right type of growth medium. Please feel free to write with questions or comments to askthedoctor@htgsupply.com, I would enjoy hearing some of the combinations of growth mediums you have used, which are the best and worst etc.

Hydroponics mediums
Pottings soil
Starter plugs

Good Growing,
Dr. E.R. Myers



Vermiculite -- Vermiculite is essentially heated (about 1100° C), popped mica chips. It has a high cation exchange capacity (i.e., can remove positively charged ions from the soil and slowly release them) and contains magnesium and potassium. It is available in variable sizes, the larger sizes are better for larger containers. Vermiculite can absorb over 15 times its weight in water and provides plenty of air spaces so it increases water retention and to a point aeration. I say to a point because it can hold too much water, you should not use fine grade vermiculite in containers larger than one gallon or it will get too soggy. Adding sand or gravel with the vermiculite will improve drainage. Vermiculite breaks down into smaller pieces over time. You can use 100% pure fine grade vermiculite for small containers/seedlings. One hundred percent vermiculite can be used for seed germination, rooting cuttings, outdoor transplanting as well as bulb and tuber storage. Vermiculite is even used to incubate turtle eggs at the Darwin research center in the Galapagos islands.
Vermiculite is a finite resource. Horticulture grade vermiculite is mined largely in Georgia and is near neutral in pH. You should know that building or insulation grade vermiculite is alkaline, coarser and often treated with chemicals; it should not be used to grow plants. You should avoid breathing the dust from vermiculite. Keep it wet when working with it just like perlite above

Good Growing
Dr. E. R. Myers

Click here if you wish to purchase Vermiculite from HTGSupply.com



Perlite – Perlite is not a trade name but a generic term for naturally occurring expanded puffed volcanic glass. Perlite is a finite resource. It is crushed, heated and expanded lava (actually volcanic sand) that has no mineral nutrients or buffering capacity. It is made like popcorn, moisture trapped in the lava particles causes them to rupture when heated to above 755 °C. Perlite is less collapsible than vermiculite (see next post) and has a neutral pH (approximately 7.0). It is lightweight with a rough surface where it traps molecules of water. It does not absorb water which means it greatly improves drainage but provides minimal water retention. Perlite comes in grades (sizes) with the more course grades being better for larger containers. Perlite is very dusty when dry, and the dust is harmful to your lungs. Always wet perlite before using it, I use a water bottle mister/sprayer to moisten the inside of a bag or if I am making up a big batch of grow medium I put the hose and nozzle right in the big bag and soak it. It is especially good for starting cuttings, sometimes mixed with vermiculite or sand. I have read studies that show good growth with perlite hydroponic systems. Other benefits of horticultural perlite are that it is sterile and weed-free. Indoor growers know its light weight makes it ideal for use as an additive in any container growing. If you use a lot of perlite in with your soil your containers won’t be as heavy. Use too much perlite and they may tip over easy.

Good Growing,
Dr. E. R. Myers

Click here if you wish to purchase perilite from HTGSupply.com


THREE Basic Hydroponic Mediums

Clay Pellets – This man-made product is often called grow rocks. It is made by baking clay in a kiln. Inside the clay pellets are tiny air pockets (much like lava rock) which makes this a light weight medium (some of the pellets even float). The pellets are great for ebb & flow systems or other systems that have frequent watering cycles. Clay pellets do not retain much water so they need to be watered often so that the roots of your plants do not dry out. You can also mix pellets with other growing medium(s) which will increase aeration (increase water drainage decrease water retention). Expanded clay pellets are rather expensive but are reusable, which makes them a good choice for the long term. After you harvest your crop you can wash the clay pellets to remove all the old roots and then sterilize them with a 10% bleach and water mix (one part bleach to 9 parts water). Rinse the pellets with a lot of water before you use them again, so there is no bleach residue. The grow rocks can also be sterilized by using a 10% mixture of hydrogen peroxide and water. I have read that hydrogen peroxide is a more environmentally friendly way to sterilize things compared to bleach. Clay is a finite resource, but the fact that you can recycle the pellets indefinitely makes them green, if you do in fact reuse them indefinitely.
Gravel – Gravel was traditionally used as the only medium in hydroponics because it is easy to clean, never locks up nutrients and is cheap. It is also a good additive for heavy soils because it creates spaces for air. Gravel made of limestone should not be used; it will affect the pH of the medium. I have never used silica stone which is sold by HTGSupply.com but I imagine that it is a similar product in that it is suitable as a hydroponic medium and can be used as a soil amendment to increase aeration. Gravel and stone are a finite resource, but the fact that you can reuse them indefinitely makes them environmentally friendly. You can sterilize them the same as with clay pellets.
Rockwool – Rockwool is a very popular growing medium. I have used it for many years. Rockwool was originally used as insulation and was called "Mineral Insulation". It was developed for gardening in Denmark and is used extensively around the world for "Drip-Style" hydroponic systems.
Rockwool is a finite resource. It is made from stone which has been heated then extruded into thin stands which are like glass wool. The process is very similar to making cotton candy. You can buy Rockwool in blocks of different sizes. Small blocks with a preformed hole for seeds/ cuttings and medium and large blocks to transplant into as the plant grows. It can be used in any system but as I said is often used with drip emitters. I like to grow in dirt, but I used to start plants with a flat of Rockwool and then transplant each little one inch cube into a soil container. This made starting plants easy and minimized the transplant shock. Some other reasons I liked Rockwool is that it holds an incredible amount of water which gives you a "buffer" against power outages and pump (or timer) failure. Even better it also holds air, Rockwool holds at least 18 % air at all times (unless it is sitting directly in water). This means that it is practically impossible to over-water (Note I said practically impossible). As with any medium, there are disadvantages: Rockwool should be pre-soaked for 24 hours before use while most other growing medium only need to be well watered. Rockwool has a high (basic) pH which means if your plants don’t like a high pH you have to adjust your nutrient solution. As with any particulate matter, the fibers and dust from the Rockwool are bad for your lungs. Wear a dust mask when handling to prevent problems. Rockwool is hard to dispose of, if buried it will last indefinitely but so will sand, perlite and gravel. I have transplanted plants outdoors that were started in small one inch cubes and the cubes are still there years later. However, they were incorporated into the soil ecosystem and were showing no ill effect to the transplanted plant or surrounding plants. Rockwool can not be reused as the roots grow into and through it and since it is made from rock, it is not a sustainable resource. I have not used it in over a year.

Good Growing
Dr. E.R. Myers


A Limited resource Peat Moss

Peat or sphagnum moss is harvested from bogs and peatlands of North America. These are delicate habitats that do not recover from harvest. It may have taken decades for the peat moss to form. What it is, is the partially decomposed remains of bog plants, especially sphagnum moss. The sphagnum naturally makes this medium acidic (pH 3.8 - 4.5). It takes many years for sphagnum to grow a few centimeters, so it is an unsustainable resource. If you are concerned about how you use resources on our planet, you may want to steer clear of peat moss. I no longer use and don’t recommend others to use peat moss. That being said it is possible to use peat moss alone like coir as your sole growing medium, but like coir I used it with another growing medium, such as perlite, top soil etc.
Sphagnum moss like all mediums comes with its own pro’s and con’s. Sphagnum deteriorates quickly meaning that you may need to buy it often. Another problem is that if you use a recovery type hydroponic system, the small bits and pieces can clog up your hydroponic system, inhibiting the flow. As I mentioned, peat moss is very acidic so you will have to adjust your system to get your pH into the optimal range. A benefit is that if you supplement your growth medium with less than 20% sphagnum moss you can minimize all the disadvantages and still enjoy the benefits of sphagnum holding onto nutrients to prevent burn and releasing the nutrients over time helping to reduce toxic buildups. But I would use coir instead.

Good Growing,
Dr. E.R.Myers


The renewable organic amendment Coco Coir

When coconut’s are harvested the juice inside is coconut ‘milk’ and the stuff you eat is the white inside. The ‘waste product’ brown husks today are used to create Coir brick "peat" as a bi-product. It's mostly organic matter so it is a good additive, As with any organic matter it will aerating clay soils or hold moisture in sandy soils. Coir brick "peat"can be used alone to grow your plants or as a way to amend soil. Coir brick "peat" is consistent and uniform in texture (homogenous). It has a pH of 5.7 to 6.5, plus a high cation exchange capacity meaning that coir will hold and release nutrients in solution over extended periods. Moreover, having a slow degradation rate, it conditions the soil and promotes the development of a consistent pH level.
As far as being green, Coir brick "peat" is a natural alternative to mined peat moss. Using coir products means you help slow down peat extraction from environmentally sensitive bogs world wide and provide a demand for a former waste product, often from a less developed nation. As with any resource, it can be overharvested, but it seems to be a green way to grow. I have grown plants using just coir and used it as a soil additive, I like it better as an additive, there seems to be a need for Mg and Ca when you use it alone. An easy problem to fix with many fertilizers but a problem nonetheless.

I have also written and grown with a coir-soil mixture, please click here to read that post next.

Good Growing,
Dr. E.R.Myers


Cheap soil amendment for aeration -- Sand

Sand is one of the principal components of soil, being any particle that measures 2mm – 0.05mm. It is also easily available at garden stores and hardware stores.  (I have also written about how to use sand to control soil grants) Sand is an inexpensive soil amendment that makes it easier to work a garden outdoors and allows container plants to drain water meaning sand provides plenty of aeration (keeps the roots from getting too soggy). In general it dries rapidly and easily loses nutrients so you do not have to worry about toxic nutrient build up via sand. Sand comes in different sizes or grades; they all seem to work well as soil amenders. I like to mix one part sand with 4 parts potting soil but you can add more sand if you tend to water you plants a lot. Sand can also be used with other inorganic growth mediums since it will increase the weight of containers and the smaller particles (compared to perilite for example) will help the plant “hold on” firmly with its roots. There are several types of sand, depending on the area you live in. Sand with limestone will raise the pH. Sand may contain salt in salt water areas, salt will be toxic to most plants and needs to be removed from the sand. You can do this by soaking the sand in tap water for a day. If you have a heavy clay soil in your outdoor garden or you are looking to loosen up and make a lighter indoor soil give sand a try.

Good Growing,
Dr. E. R. Myers


The Best Grow Medium (my favorite anyway) potting soil

Potting Soil -- Potting soil is basically topsoil (the top of the soil from somewhere). If you buy a product that says potting soil it is made up mostly of topsoil with various amendments. Potting soil is high in nutrients and organic matter. You can even get your own from outside.  You may want to sterilize it to remove pests especially if nematodes are common in your area. You can sterilize the soil by putting it in the oven at the maximum temperature for an hour, or simply put it in the microwave for 5-10 min until it is steaming. However, it is easier to buy amended topsoil than worry about weed seeds, pests, and diseases which will thrive in your controlled indoor environment, often at the expense of your favorite plants. Moreover, home-dug top soil, even from one area can vary in pH, texture and water holding capacity. If you want something consistent, you can buy various potting soils from HTGSupply.com. Commercial potting soil is usually amended or “lightened up” meaning things like perlite vermiculite peat moss etc. have been added so that the soil does not stick together and plant roots can easily move through the soil. There are specialized commercial potting mixes containing mild fertilizers, additives to help hold water, balance the pH, some even have microorganisms. If you are just starting out, or having problems with growing plants, I recommend using potting soil like fox farm or pro-mix. It will provide nutrients to the plants for several months and most every plant can grow well in these type of potting soils.
The most important thing with soil is soil texture (also see SOIL 5/08). You want something that will hold some water but drain well to allow air to enter the growth medium. Mixes that do not drain well will have low oxygen available to the plants and will have poor plant growth for most plants. An easy test is to grab a handful of your soil and squeeze it. It should stick together, but fall apart if you poke it. If it does not fall apart you need to amend you soil to loosen it up. There are several soil amendments, some can be added to soil, or you can even grow without topsoil (soilless mixes). Soilless mixes tend to have no or low nutrients so they require fertilization at all stages of plant growth. In some cases, if you are using just a soilless medium it can be considered growing hydroponically since all nutrients are added via water solution to the medium the plants are growing in.
Soil can be a renewable resource, but can also be exploited. Once I have used soil indoors, I often add it to my outdoor garden to improve the soil of my outdoor gardens. Soil will lose its nutrients after a growing season or two. You can continue to use the soil but will have to add all nutrients and may risk build up of nutrients to toxic levels. You could flush out your soil between growing cycles like you clean certain hydroponic mediums. In essence, if you use dirt long enough you are growing hydroponically, you are providing all nutrients, maintaining Ph etc.
If you want to be more involved with the uptake of nutrients with your plants, you may want to use soilless mediums since their lack of nutrients means that you must provide (control) all nutrients in all stages of plant growth. Potting soil is easy to use because it provides some nutrients so it “buffers” against too little nutrients, and since it is able to hold onto nutrients, it “buffers” against burning plants with too much fertilizer. Be mindful that soilless mixes allow you to have more control and perhaps maximize impact of nutrients, but they also lack the margin of error that soil provides. Once you can grow great in soil, you may want to move on to hydroponics or try other growth medium mixtures. I have tried many grow mediums, and I still keep going back to soil. It is what plants evolved to grow in, it can be a living thing by itself feeding and nurturing your plants.

Good Growing,
Dr. E. R. Myers


GROW MEDIUMS -- Which One Is For You?

For the next few weeks, I will be discussing various grow mediums. I have not used all, and some of this information will be what I have read. Please feel free to add your personal experiencesto via posts and I welcome questions, comments etc. via E-mail at Askthedoc@htgsupply.com

Growers have a wide choice of growing mediums and techniques from growing in the ground, to growing in containers with dirt or soilless mixes to growing via hydroponics. I will try to point out the good and bad aspects of different mediums, so that you can use or create the best medium for your plants. I have also included some information about which products are “green” and which are not. Green meaning the mediums are renewable and minimally if at all harmful to the environment.

All good plant growth mediums will have a uniform consistency and provide sufficient moisture, adequate aeration (pore space for oxygen), and be firm enough to support the plant. You also do not want it to contain unfavorable substances like toxins, diseases, or pests.

Good Growing,
Dr. E. R. Myers