Root growth/mass(all other factors being equal)
is also one of the major concerns for indoor growers, who generally cannot move to bigger and bigger pots to allow for bigger root masses.
However, a lot of container space often goes unused, because roots will not grow into the top inches of soil that are often dried out from powerful lights and low humidity. In addition, since MJ soils are typically very airy and light, when watering the top inches of soil are easily disturbed as the dirt is pushed and moved around by the water. This also inhibits roots from growing into the top inches of soil.
In a 1 foot tall pot the top 3 inches of soil will not allow root growth, you are wasting 25%
of your soil mass that could be used for roots. In pots that are wider at the top than the bottom, this wasted soil could be even greater!
How then to use this soil?
We need to prevent the soil from being disturbed and keep it moist, and hydro growers have been using an ideal product for this for a long time - Hydroton clay balls!
Hydroton clay balls are LIGHT
They won't compact your soil the way putting pebbles on top would.
A layer of hydroton clay balls on top of the soil will help the soil underneath it lose moisture through evaporation and low humidity.
By adding a layer of hydroton on top of the soil, soil disturbance is prevented since the water does not directly touch the soil until it has filtered through the layer of hydroton balls. Soil moisture is then trapped underneath the hydroton and less likely to evaporate due to heat and/or low humidity.
This way it is possible to grow plants with roots stretching up all the way to the top of the soil. Those roots will rapidly provide nutrition to the plant when it is watered. It also will help the plant be able to go a longer time without watering since moisture that would have been lost to evaporation is now available to the plant.
Use a root stimulator during veg growth to help accelerate the root growth process and make sure there is a strong root mass in flowering. The last things you want in flower are wimpy roots (unless you want wimpy yields).