A "How-To" Guide for Watering Plants in a Greenhouse
One of the great things about running a greenhouse is the level of targeted care that you can give to your plants. They are all in one spot, and their basic needs can be addressed in a way that would be hard in a field setting. Having some control, even a little, can be a great thing, when the real art of farming is learning to work in a system where we are actually less in control than we might like. Water is one of the more important pieces in the greenhouse, and how, when and with what you are watering can make a big difference.
I have been tempering my water for years, and am very aware of the impact that it has on the plants. Where I live, water comes out of the ground at 50 degrees. I realize plants aren’t people (don’t tell them I said that), but taking a shower at 50 degrees stops me in my tracks, and then it takes me a long time to recover. Your plants feel the same way. Using cold water not only shocks the plants; it also shocks the soil biology that’s feeding my plants. I am using a compost based mix, where the nutrition that is available to the plants is made so largely by biological activity. That population thrives when the soil is warm, not when it’s cold. Before I had my boiler, I had a hot water hose bib hooked up in my house, and I would blend a mix of hot and cold water to get a mix that was at 90 to 95 degrees when it hit the plants. They loved it. I now have a plate heat exchanger in the greenhouse that I can adjust the temperature based on the output of the nozzle that I am using. If all this sounds a little over the top, consider the value of the plants that are in the greenhouse at any one time. They truly represent a large fundamental piece of the profitability of your season, and they are worth the time and effort.
As for the how of watering, there are lots of different nozzle choices, and each has a place. I use a very low volume, fine mist for setting seeds after I seed a flat, or for setting new seedlings. I like to set the soil with the lighter flows for the first few days and longer if the seeds are small, so that all the care I took in placing the depth isn’t disturbed by a torrent of water. I have other nozzles with a heavier flow that I use for putting more water down when I am watering the greenhouse when needs are high. I keep the wand moving, so that there is never water pounding on the trays. A series of lighter passes allows the water to penetrate better than one heavy soak, and it’s a lot easier on the plants.
When you are watering is also important. Sometimes it seems obvious; plants are dry, they need water. Not always. Plants like water, but they don’t want to be wet. Excessive moisture in the greenhouse can lead to fungal diseases, as well as creating an environment for certain pests to thrive. I am very conscious of the local weather when I approach watering. My ultimate goal is that at the end of the day, the plants are dry going into the evening. If the day is going to be sunny, and a heavy water use day, I put on the water first thing in the morning, while the sun is still low in the sky. This will give the plants the chance to shed the water before the sun is high. It is possible for an intense sun to turn that drop of water on a leaf into a little lens and cause burning on the leaf. If I am away during the day, I will come back and water in a more targeted way for plants that are showing thirst, and do a final watering in the afternoon.
Some of the trickiest times for water management are during longer periods of cloudy weather. The plants needs for water are much lighter, and you should adjust accordingly. Switch to a lower flow nozzle, and be really careful about overwatering. Plants are pumps, and they have a tendency to take up the water that they have available. On a sunny day they can use that water, and it is easy to get rid of it. During prolonged cloudy weather, plants have a reduced ability to photosynthesize. Excess humidity also makes it harder to expel water, and that water can build up in the cells of the plant and cause them to rupture. The result will often appear as blisters on the leaves. This is called edema, a physiological condition, which will usually pass when the conditions change. It’s still best to avoid the problem in the first place though.
After a year or three of dragging a hose around on the ground, I made the jump to an overhead water line, and I love it. It’s safer, as there aren’t hoses laying around to trip on, and I have fewer tantrums, as there aren’t hoses laying around to trip on. It’s also a lot cleaner, because the hose isn’t being dragged around on the floor. They are available as kits from greenhouse supply companies, but are also easily fabricated from hardware store parts. My greenhouse is 22’ wide, and one run allows me to get to all the corners of the greenhouse. Super handy, and I can’t imagine not having it.
A little extra attention in the greenhouse makes a big difference, and the value is there. Strong, healthy plants are one of the most important parts of your farm. By the way, my plants love country music.
All my best,