Dear Danko: Expert Grow Advice On Trellising, Making Hash, And More

Hash leaves, vapor-pressure deficit, transplant shock, ScrOG and more.
Dear Danko: Expert Grow Advice On Trellising, Making Hash, And More
Trellising greatly increases yields when done properly/ High Times Archives

High Times’ cultivation specialist Danny Danko answers all your burning questions about being the best grower you can be. But first, some quick tips from the expert himself:

  • Transplant clones into larger containers as soon as you see roots coming out from the bottom of your chosen rooting medium.
  • Oxygenated compost tea can be used as a foliar feed or a soil drench for a mild dose of nutrients.
  • Always quarantine any new clones coming into your grow space in a separate area to prevent the spread of pests and pathogens.

Subject: Screen of Green
From: Kind Ray

I keep hearing about the “screen of green” technique, but I can’t really figure out what it means. There’s lots of conflicting info online. What exactly is it, and how can I use it to increase my yields?

Dear Ray,

The “screen of green” technique (also known as ScrOG for short) is a trellis-based plant-training method that maximizes harvests by utilizing all available canopy space. A screen made from string, nylon netting or metal chicken wire is secured horizontally above plant level.

As your plants grow to reach the height of your chosen trellising material, you physically guide and tuck the individual shoots and branches into the empty spaces in the screen. As you approach the flowering stage, most if not all of the holes become filled with shoots that will each become a flower.

Keep in mind that in order to use ScrOG properly, you will need to increase your vegetative time to fill out the screen. The extra few weeks of vegging will result in larger harvests, but you must factor in the added time to your growing schedule.

Many ScrOG growers remove the lower branches below the canopy in order to stimulate more growth up top. Because the buds fill out so closely together, air circulation is very important at canopy level to avoid mold and growth stagnation. ScrOG-style growing is also a great way to tame stretchy, longer-flowering sativa-dominant strains as well.

Subject: Hash Leaves
From: C.D.

I’ve seen a few videos on making hash from trimmings, and it looks like it takes quite a bit to make it worth the time and effort. I’m a beginner grower (about to start my first grow within the next two weeks), but I will only be raising 1-2 plants per grow due to space issues. Can I keep and store my trimmings until I have enough to make hash, and, if so, how would I keep them so they don’t lose all that goodness? Thanks!

Dear C.D.,

The amount of trimmings you’ll collect from just a couple of plants in a small space will not produce very much hash at all. If you’d like to store the trimmings from multiple grows, freeze them in a light-tight bag and keep them in the freezer until you plan to make the hash.

You can also consider cooking with the trim to make a cannabis-infused edible product, and you may get more bang for your buck that way. If you’re patient, however, you will eventually accumulate enough trimmings with which to make hashish, so you’ll want to decide if you want to use the dry-sifting method or ice-water extraction. Either way, nothing beats a packed bowl of your own handmade glandular trichome essential-oil concoction!

Subject: Vapor-Pressure Deficit
From: Jimmy Conway

My guy at my hydro shop keeps talking about VPD. I know that means “vapor pressure deficit,” but I’m too embarrassed to admit I don’t know what that indicates exactly and why it’s so important. Can you help?

Dear Jimmy,

To understand vapor-pressure deficit, or VPD, you must first understand relative humidity (RH). If your air is too dry, your plants will transpire more, releasing moisture through their stomata. If your air is more humid, the vapor pressure rises and the leaves transpire less. VPD is the difference measured between AVP (actual vapor pressure) and SVP (saturation vapor pressure).

Basically, it’s an advanced-level metric that takes into account air temperature, leaf temperature and relative humidity to dial in your environment for optimal growth rates. If the VPD is too high, your young plants will take in more nutrients than they need and can become toxic. As your plants mature, the VPD should rise a bit to accommodate for more transpiration. Use humidifiers or dehumidifiers to raise and lower VPD rates.

Subject: Transplant Shock
From: Patrick O.

Should I transplant from a 5-gallon pot into a 15-gallon pot? These are outside plants. Would it stress out the plant too much?

Dear Patrick,

The degree to which transplanting can hurt a plant depends on when it’s done and how gently it’s accomplished. Any transplantation should be done during the vegetative stage of the plant’s growth and not during the flowering stage, or ideally even during the two to three weeks leading up to the flowering stage.

No matter how gently a plant is transplanted, it will take from a few days to a week to recover from the shock, and you can’t afford to lose this time during flowering while the plant is supposed to be using its energy to pack on buds. The only exception would be a heavily root-bound plant that needs to be transplanted during flowering, but this is a complication that should have been avoided with an earlier transplant.

First, water the plant in its original pot thoroughly to ensure that the soil and root-ball stay together without crumbling apart. Prepare the new, larger pot with some of your planting mix and then gently remove the plant from the original pot. I like to hold it by the trunk at the base and turn the entire pot upside down. Place the plant into the new pot and backfill the remaining mix around the outside. Water it and fill in any remaining gaps, keeping in mind that the plant may droop for a few hours before bouncing back strong.

Subject: How Long to Vegetate?
From: Fish Apple

How long should I keep my plants in their vegetative stage indoors before flowering? How many weeks do I let them grow bigger, and how tall will they get before that time?

Dear Fish,

One of the advantages to growing indoors is that you get to pick and choose when to begin flowering your plants (as long as they’re not of the auto-flowering variety). This means if you want smaller plants, you begin the flowering period after a week or two of vegetating, and if you want larger plants you can wait over a month to let them develop.

Seedlings or clones require at least 18 hours of light to thrive and stay in the vegetative period. During this time, your plant will grow many fan leaves, and new shoots will form into tops and branches as your root system expands into its medium. You trigger the start of the flowering period by changing your light timer to a 12 /12-hour day/night light cycle. This mimicking of summer-to-fall lighting will cause the plant to begin forming flowers instead of expanding ever larger. Keep in mind that there’s a stretching period of several weeks as the plants transition, and they will continue to grow during this time. Soon you will see the white-haired puffballs at the ends of your branches that will eventually become thick colas of cannabis flowers.

One rule of thumb that I recommend in order to avoid having your plants become too root-bound is to vegetate one week for every gallon of container—meaning plants in 1-gallon pots vegetate for a week, while those in 4-gallon buckets vegetate for one month. The longer the vegging period, the bigger the yield, but this requires larger containers to support bigger root systems.

Subject: Flower Time
From: Harry M.

How long does it usually take to see colas form after the 12/12-hour day/night light cycle has begun?

Dear Harry,

You should begin seeing tiny flowers begin to form within one to two weeks of switching your vegetative cycle into flowering. Some longer flowering sativas can take up to three weeks or even a month to start forming flowers, but most of the hybrids available today will show buds earlier. Baby female flowers look like little puffballs with white hairs pointing upward. Males will look like tiny clumps of bananas and point downward.

Subject: Heat and Lighting
From: Overwhelmed Husband

I’m a nonsmoker with a cannabis-patient wife in the southern Great Lakes area. I’ve decided to stop relying on others for my wife’s medicine and made the decision to grow some different strains for her. I’m a total rookie when it comes to growing weed, though, and I’m piecing together a setup. I currently have a 3′ x 3′ tent that I’m able to fit into a walk-in closet. I’m getting a 4-inch vent/carbon-filter setup that will vent room-temperature air (68° F) into the tent and out into an attic, with the tent being negatively pressurized. I have many questions, but I’ll keep it only to two.

First, should I heat the incoming air?

Second, what light should I get for a 3′ x 3′ tent that can veg and flower? I’m going to start off with two plants and hopefully get to six rather quickly.

I’ve weighed my options and I think I’ve narrowed it down to LED or CMH. But maybe I’m way off and I should be looking at MH and switching to HPS to flower?

Dear OH,

First, you do not need to heat the air coming into your growing space. Sixty-eight degrees is fairly ideal, and, depending on the light you choose, the temperature may be somewhat higher in your space, so act accordingly. Be sure to bring the cool air in from the lower part of the tent.

LED (or light-emitting diode) lighting will create less heat, but you may not be pleased with the size and density of your buds. CMH (or ceramic metal halide) lighting generates more heat, but will also result in a heavier harvest of full buds. My suggestion is to go with the CMH lighting but invest in an exhaust fan to remove hot air from the upper level of your tent.

Send your cannabis-cultivation questions to

Originally published in the September, 2019 issue of High Times magazine. Subscribe right here.

  1. It is misleading to state bring in air from the lower part of your tent, better to say exhaust hotter air from the upper area of the tent and bring cool air in at canopy height,(tops of plants) far better to maintain even temperatures, stay under 82F and drop to 65F at lights off.

    1. UM your kind of wrong, having a inlet for incoming air at the lowest part of the tent will bring in the coolest air. (its science)
      I have 3 grow areas and all 3 have an inlet near the floor( to bring in cool air like the article says)
      and an exhaust fan at the top of the area to exhaust the hot air.
      The simplest way to look at it, We all now hot air rises and cool air sinks, so having the inlet very low is the best way to get the coolest air into your grow-room or tent and exhausting the air closest to the top because as we know heat rises, so the hottest part of your room would be the top. I use a sealed hood and exhaust the heat out the top, the bottom of the room has an air in take, so the air flows from the coolest part and all the heat rises out , its an airflow you create that keeps your area nice and cool. the exhaust fan is drawing cool air from the bottom of the room and distributing it evenly. it simple science of cold air sinking and warm air rising, use it to your advantage.

      1. Another advantage to having the inlet very low, is light leaks.
        I have a room within a room so I can have a 18/6 area and a 12/12 within the same room.
        light leaks might effect your 12/12 and make your plants not flower properly.
        Having your inlets very low to the floor make the any light leaks very small, because the hole is so close to the floor the light doesn’t leak out very far and is easier to control. If you put a hole at the level of your canopy the light leaks may be larger and will now obviously effect your canopy because its at the level of the canopy.

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