When starting out your water reservoir should be over-filled to give the small roots access to water. The roots must be submerged, if not the plant will not be getting any water. If you are using a very large reservoir (40 gallon+) it sometimes helps to start the plants in a smaller reservoir.
Use the Nutrient Calculator to mix up a batch of water using the “Mild Vegetative Growth” ratio. Don’t forget to add pH down to bring your water down to pH 5.5. Aim for a target VPD between 0.6- 0.9 during early veg and 0.9 and 1.2 during regular vegetative growth
After the roots are established it is not recommended to fill past the bottom of the net pots.
The light should be dimmed down to 50% power to start. If there is no external dimmer provided with your lights use a small Phillips screwdriver to turn the dimmer down on the LED Driver. The light should be 24-48” above the plant during vegetative growth. Slowly increase the power of the light so that you are up to 100% by the time flowering starts.
Light Burn – is a risk with LED Boards. If the leaves start to curl up on the edges or have a “3D” look you have too much light. If the light is already at 50% and you have no more room to raise it up further a piece of cardboard can be rested on your trellis net to give the plants some shade from the LED as they adapt to the high photon light source. Remember that LED Boards put out some serious light and the high PPFD can easily fry young plants.
In DWC, vegetative growth takes 2-3 weeks on average, much shorter than with soil. The goal of vegetative growth is to get enough growth to reach the corners of your Scrog screen. You do not want to the plants to start growing through the screen. The first 2-3 weeks of flowering will still be vegetative growth anyways. What I mean by this is that day 1 of flower is measured by when you flip your lights from 18-6 to 12-12. The plants do not magically start to flower the same day, so day 1-21 of ‘flower’ or 12-12 light phase are usually aggressive vegetative growth as the plants transition into their flowering phase.
During early vegetative growth it is VERY important to maintain adequate Vapor Pressure Deficit (VPD). To keep VPD low enough to keep the plants from getting stunted I typically use a humidifier set to 60-70% humidity depending on the temperature. As the plants grow they are able to transpire moisture into the air very effectively and I typically switch from a humidifier to a dehumidifier at about week 2-3 of veg or at the start of flower.
I strongly recommend the use of a SensorPush or Pulse system for monitoring VPD and setting alerts to let you know if VPD drifts out of range.
