Determining Irrigation Needs in a Greenhouse.....

Irrigation is a vital part of growing seedlings at a nursery and there are many different ways in which you can determine the plants need for moisture. It can be as simple as feeling the soil with your hands or as complex as using a digital soil moisture sensor. The bottom line is that plants require water to survive and carry out photosynthesis and one of the most important jobs we preform daily at the nursery is tracking the plants needs and supplying the trees with water when required.

Styrofoam block of trees, this block contains 112 plugs

Well rooted Ponderosa pine seedling.

Many of the container trees we grow within the greenhouses are propagated in large styrofoam blocks. Each block may contain anywhere from 45-160 cells in which a tree is grown and each individual cell is called a plug. Trees grown in this manner have become very popular with our clients due to their ease in planting and containerized trees have very much become the wave of the future.

To determine the irrigation needs within each greenhouse we use a system in which we establish "block weights" from a group of randomly selected styrofoam blocks set in various parts of the greenhouse. It's a fairly simple way to track the water saturation levels of the trees in each greenhouse and takes the guess work out of determining our daily irrigation needs.

Taking our daily 'block weight'

First, we select 5 blocks at random points within a greenhouse and mark the block with a flag. Each flag has a number from 1-5 so we can track each individual block of trees. Next, to establish our fully saturated block weight we irrigate the greenhouse and wait 45 minutes to one hour after the water has finished, we weigh each block and record the weight. This number is what we call our "base weight" and this is the weight at which the trees are fully saturated with water and this is recorded as 100%.

Once our base weights are established our irrigation protocol tells us that each greenhouse should be irrigated when the blocks get no lower than 70-75% saturated. Part of my job is to monitor this daily, so I begin each morning by making my way through each greenhouse and checking the block weights to see where the watering needs are at. This is a great way to monitor water usage and it also allows me to visit with the trees daily to check for any other issues that could arise throughout the growing season such as pests problems or disease.

Flagged blocks within the greenhouse.

The process is pretty simple, each flagged block is taken to a scale and it's weight is recorded, then this weight is converted into a percentage by dividing our current weight by the established, saturated block weight. If the average of the 5 blocks within the house falls at or below 70-75% we will turn on the irrigation and water the greenhouse and the process starts all over again. Depending on weather conditions and the time of year the trees may need to be irrigated daily or sometime it may be 2-3 days between irrigation.