6/30/12

E-mail - What is a Lumen, and How Much Do I Need

Hey Doc,

    How many lumens per square foot should I have in my garden? What is a lumen anyway?

A lumen is a unit to measure light coming from an angle or a source (like your grow light). A lux is another unit of measure, it takes into consideration area. It is complicated, but basically the larger the area you consider, the lower the lux you get with the same amount of lumens. Lumens are the output, lux is a measure of that energy over an area. There are two types of lumens, luminous flux which measures light that is visible to the human eye, and power or radiant flux, which measures total output. If you are going to measure your grow lights in lumens, you want to use radiant flux. Plants and the human eye both have pigments so we can see color, and plants can absorb lights energy. We have different pigments though, so comparing what we ‘see’ as color, to what plants need to drive photosynthesis is, well comparing apples to oranges. It does not correlate to good growing!

I do not like the lumen (or lux) for measuring light for plant growth. One reason is that lumens would include green light in its measurement. However, plants do NOT absorb green light, they reflect it. So, you could have a grow light that emits a good percentage of its energy in the wavelength of green light, and it would register a high lumen output, but the electricity you are buying to run this high green output light is not available for plant growth.

Good growers may want to read my post comparing light intensity of MH and HPS

6/28/12

How to Use Beneficial Products for Optimal Results

When you add beneficial organisms you are altering the rhizosphere. You want to increase the number of organisms that benefit your plants growth, but to do this you need to get the microorganisms to the rhizosphere.
Make sure you saturate the soil completely. You would be wasting the product if you just water the top of the soil and the organisms cannot get in contact with the plant roots. Also, do not over water, you want the water/product to come in contact with the plant roots, but not sit in the trays under your pots.
Using Beneficial’s can mean more nitrogen fixing bacteria, or more chelation chemicals that help with the absorption of nutrients with your plants or various fungal mycorrhizal species with help plants to absorb nutrients from the soil. I have personally tested and used the Roots Organics and Stump Tea sold by HTGSupply.com. If you have not used these products, I highly recommend doing a scientific test  .Use it on some plants and not others of the same type, and compare growth, yield flavor and color of your groups to see if there is a benefit. I know you will be happy you did.
Good Growing,
Dr. E.R. Myers

6/21/12

How Late Can You Put Plants Outdoors and Still Get a Harvest?



I had an E-mail about starting plants later in the summer, but the sender did not want his actual E-mail used on the blog… The sender had started some seeds indoors and life had gotten complicated and the plants were still in small pots under a fluorescent light on/off - 20/4. It is late June and the first frost won’t be until early October, assuming a normal year.

It is a great idea to start your plants indoors for an outdoors garden.  You can still put your plants out in late June or even a bit later in the summer. The problem is your plants will be smaller so you will get less of a yield. It would still be great to put out a tomato or pepper plant in July and only get 2-3 peppers than throw the plants on the compost pile and get no peppers.
Some things to keep in mind... If the plants are root bound, you will want to break up the roots to they do not keep growing around in circles. Some people suggest using a clean sharp knife and making 3-4 incisions along the sides. I tend to break the bottom of the root mass up so the roots grow down.
You will also want to keep the plant watered well, one because you will damage the roots when you break them apart but also secondly in your situation I assume the plants have a pretty small root system compared to the above ground biomass. It will take a couple weeks for the roots to grow deep enough to support and supply the plant with water.
You may also want to space your plants CLOSER together since they will not get as big as normal. When growing indoors, it is possible to increase yields by growing lots of smaller plants vs. a few large plants. I do not know if this is the same for outdoor growing, since plants do not have the special limits they do indoors it would be better to start plants early and have them get as big as possible.
You may be tempted to add a high nitrogen fertilizer, but this may lead to the plant growing vigerously in vegetative mode and you may not get flower/fruit set. I would still give the plant some nitrogen, but I would recommend the phosphorus be the highest number.
Good Growing,
Dr. E.R. Myers

6/14/12

Soil and Water Availability I

The medium you use, affects the water holding capacity which will then affect the rhizosphere and over all plant metabolism.. One of the main functions of soil is to store moisture and supply it to plants between watering.  Knowing a soil's texture will help you know what you need to do to improve your soil.  Good growers know that evaporation from the soil surface, transpiration by plants and water drainage by gravity combine to reduce soil moisture between water applications. If the water content becomes too low, plants become stressed. The moisture storage capacity of a soil provides a buffer which determines a plant’s capacity to grow at an optimim rate.
The number one reason plants do not do well or die indoors is that people overwater them. Yes you can love and care for your plants too much.
The problem with over watering is that there is no longer oxygen available to the roots. Roots need BOTH oxygen and water, too much of either will slow growth and limit yields

High H20 = low oxygen, root physiology slows and stops. You will notice leaf yellowing
Low H20 = lower rate of photosynthesis, leaf physiology, specifically photosynthesis will slow and stop as water becomes unavailable to plants.
The amount of water held in a soil is a function of the pore size (cross-sectional diameter) and pore space (total volume of all pores) A balance results due to pore space - big pores drain freely small pores retain H20, a good medium will have varying pore sizes.

Pores > 60 uM - gravity controls H20 in pores - GRAVITAIONAL H20
Very important in air exchange in soils promoted by sand perilite and small stones

Pores 0.1 uM to 60 uM primary source H20 for plants - CAPILLARY H20
Capillary forces hold H20 against gravity so they provide water to plants over lonter perionds Vermiculite,  small perilite particles and organic mater like coir or compost

Pores < 0.1 uM hygroscopic H20 unavailable to plants (held too tightly) Clay

1.Gravitational water is found in the macropores. This water moves through the soil due to the force of gravity. It moves rapidly out of well drained soil and is not considered to be available to plants after a few hours or a day.
Too much gravitational can cause plants to wilt and die because gravitational water occupies air space, which is necessary to supply oxygen to the roots. If you let your plants sit in water, the gravitational water can not drain.

2.Capillary water: Most, but not all, of this water is available for plant growth. Capillary water is held in pores that are small enough to hold water against gravity, but not so tightly that roots cannot absorb it.
Capillary water is held by cohesion (attraction of water molecules to each other) and adhesion (attraction of water molecule to the soil particle).

3. Hygroscopic water: This water forms very thin films around soil particles and is not available to the plant. The water is held so tightly by the soil that it cannot be taken up by roots. Clay will contain much more of this type of water than sands because of surface area differences.

The reason you want a variety of pores in your medium is because as the water is withdrawn, the larger pores drain first. The finer the pores, the more resistant they are to removal of water.  You want large pores to drain quickly so your roots have oxygen, but you want small pores to hold water against gravity and provide your plants water for photosynthesis.

Please read my next post on water availability in soil...

Good Growing,
Dr. E.R. Myers

6/7/12

How to Use Beneficial Organism Products for Optimal Results


When you add beneficial organisms you are altering the rhizosphere. You want to increase the number of organisms that benefit your plant. To maximize efficiency you need to get the microorganisms to the rhizosphere, so you need to saturate the soil completely. You would be wasting the product if you just water the top of the soil and the organisms cannot get in contact with the plant roots. You also do not want to over water your plants and have the microorganisms in the water trays under your pots. With a hydroponic system you want to make sure you water the product directly on the roots. You may get the organisms into the rhizosphere via water recirculation but I would try to make sure you maximize exposure when you first water.

Using beneficial bacteria/microorganisms can mean more nitrogen fixing bacteria, or more chelation chemicals that help with the absorption of nutrients with your plants or various fungal mycorrhizal species with help plants to absorb nutrients from the soil. All of there are found in the roots organics and the stump tea sold by HTGSupply.com. If you have not used these products, I highly recommend doing a scientific test. Use it on some plants and not others of the same type, and compare growth, yield, flavor and color of your groups to see if there is a difference and hopfully a benefit from the new product.

Good Growing,
Dr. E.R. Myers