Two of the schedule modes options in Spruce Connected Schedules utilize a Water Balance method. These modes keep a running tally of water levels for each zone. Water levels are affected by:

• Weather will reduce the water levels, in the form of evapotranspiration, or Et (temperature, humidity, and wind all affect this).
• Watering will increase water levels. 
• Rainfall will increase water levels. 

Water level additions and subtractions are expressed in inches of water, and. For simplicity, the Spruce app translates these values to a percentage and reports a “Fill Level.”

Fill Level meanings

• 100% is the upper limit of water stored in the soil the soil. This can be thought of the point at which the soil is saturated, or “full”. This is also defined by the total available inches of water in the soil that is available to the crop. This is a function of your zone’s landscape type (which determines root depth) and soil type (which determines the available water percentage accessible by the plant).
• -100% is the lower limit of water stored in the soil, that is available to the plant. This is the point below which, the plant will be permanently damaged, also known as the wilting point.
• Now that you understand the upper and lower limits of water available in the soil, the next important concept is the water level to trigger watering. This concept is known as the maximum allowed depletion percentage, which is set by the landscape type. A common allowed depletion is 50% – this means that the water levels are allowed to deplete half of the total water table before watering.
  • A 0% fill level is essentially the allowed depletion level. It’s important to understand that the 0% defined here is always the equivalent inches of water of the watering threshold. So, even if you override the allowed depletion value to 30% AD or 70% AD, the lowest allowed level in the app will always be represented at 0% fill level.

Spruce does allow for a small amount of over-saturation above 100% to account for inaccuracies that are likely to exist from the Et coefficient estimates.

Weather Balance – Vary Days

In the Weather Balance – Vary Days mode, watering will occur when the fill level will surpass the Lowest Allowed Level (0%). This will include the water loss (from weather factors) that is forecasted to occur within the same day.

Spruce will always attempt to water before the water levels dip below the lowest allowed level, but this may not be possible if the allowed watering days are too restrictive.

In this mode, when the zone is triggered to water, the watering time is determined by amount of water needed to “fill” back up to 100%.

Weather Balance – Vary Time

In the Weather Balance – Vary Time mode, watering will occur at a frequency set by the user (for example, 1 through 7 times per week). On the days scheduled, regardless of whether or not the current fill level is above or below the lowest allowed level, Spruce will water the amount needed to “fill” back up to 100%.

Which Weather Balance mode should I choose?

The recommended method of watering would be the “Vary Days” mode, because you would always want to make sure that the soil moisture levels deplete appropriately. This allows for oxygen to enter the lower root zone, and promotes deeper roots.

An important point is that the two Weather Balance modes will actually water the same amount over the course of a few weeks. As an example of how each mode would respond, as the temperature becomes cooler, or if rainfall occurs, the “Vary Days” mode would water for the same amount of time at each event, but less frequently. Alternatively, the “Vary Time” mode would water the same number of days per week, but reduce the times at each of those events.