Module Overview
In this module you will be introduced to proper watering techniques and fertilizer options and regimens for outdoor raised beds with season extension.
Learning Goals
After this module, learners will be able to:
- Describe proper watering techniques including amount, time, frequency of watering and how to know when to water.
- Identify safe water sources for freshly consumed produce.
- Describe role of fertilizer and differentiate types of fertilizers used.
- Apply proper irrigation methods and fertilization methods to their own garden space for optimal growth.
Roadmap
These items will all appear, in order, in the module.
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Outdoor Watering and Fertilizing
Watch the following view for a brief overview of watering and fertilizer considerations for raised beds. The next two pages in the module dig a little deeper into water and fertilizer.
(1 minute, 52 seconds)
Video Transcript: Outdoor Watering and Fertilizing
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All About Watering
Water is essential for the growth of plants. Fertilizer can help supplement the nutrients in soil so that your plants will thrive and provide you with the best harvest possible.
Providing the proper amount of water for your indoor growing systems is fairly straight forward. Water should be added to hydroponic units to keep the level at the “fill” line (see Module 17). Indoor seed starting kits can be bottom watered to maintain hydration (see Module 4). However, when it comes to proper watering for raised beds — especially raised beds covered with season extension — keep in mind that watering is both art and science.
Frequency of Watering in Raised Beds
The goal of watering raised beds is to hydrate all the soil. Soil holds nutrients that plants take up through roots, and this can only happen when the soil is adequately hydrated. After direct seeding in raised beds, water daily until most seeds have germinated. In general, you will need to water 1-2 times each week after the seeds have germinated to keep soil adequately hydrated IF it does not rain.
Water the soil in the raised bed when:
- The soil looks dry, especially if it starts to look “powdery”
- Plants begin to turn brownish and/or the leaves become dry, brittle, or begin falling from the plant
Overwatering is Unlikely
Watering can be tricky, and overwatering can kill plants, especially in cold weather. Keep in mind that raised beds drain well, and they tend to be very forgiving related to overwatering. Failing to water enough is a bigger threat to plants in your raised beds.
Using a Hose or Watering Can
Encourage students, staff, and volunteers to water at the base of the plant using a hose or a watering can with potable (drinkable) water. If the soil is dry, pour water around the base of each plant, counting to at least 10 before moving to the next plant.
Avoid spraying water on the plant’s leaves. Wet leaves make it more likely that fungi will germinate and grow on the plant. Wet leaves can also cause plant tissue to burn in the hot sun. You can water any time of the day that is most convenient, but watering early in the day or a cooler part of the day minimizes water loss to evaporation.
Watering Covered Raised Beds
The wonderful thing about garden fabric (also known as “season extension garden cover” or “row cover”) is that moisture from rain and snow can penetrate it to hydrate the soil. If it rains or snows, there is no need to remove the cover to let the water in.
When temperatures dip in the winter, the growth of your plants will slow down, and they will require less water. They should be able to go a few weeks without being watered by rain, snow, or manual watering. To maintain the protective micro-climate under the cover, it should not be opened until the outdoor temperature reaches at least 50 degrees. If the temperatures hover around 40-50 degrees and weeks go by without precipitation, the beds can be watered by sprinkling water directly through the covers without opening them.
Safe Water Sources
When growing food, only use potable water, such as city tap water from a sink or hose. If using water from other sources, a filter will be required. If using watering cans or other containers, be sure to rinse them out regularly and let them dry completely, whenever possible.
To avoid contamination, do not use collected rainwater on plants that will be eaten. Water from rain barrels should only be used for flowers, ornamentals, pollinator gardens, etc.
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All About Fertilizing
The Importance of Fertilization
Fertilization is different from soil health. Plants need micro- and macro-nutrients, along with structural nutrients from air and water, to grow and thrive. Use fertilization as an opportunity to discuss what all living things need to live and additional Life Science concepts with students.
As plants grow, nutrients are removed from the soil and end up in the harvested vegetables and plants. The purpose of fertilization is to ensure there are enough essential nutrients for plant growth after they have been depleted by previous growth or through leaching or heavy irrigation. Refer to Module 12 on soil testing to learn about assessing the nutrient quality of your soil.
Because soil fertility is reduced by soil depletion, fertilization needs change over time. Bagged soil generally has enough nutrients for the first couple weeks. After that, you will need to fertilize the soil as directed on the label of the fertilizer you choose. Keep in mind that seed starting fertilizer (such as “Quick Start” or “Seedling Grow”) has the proper blend of nutrients to promote germination, but not enough nutrients to sustain growth of mature plants.
N-P-K Numbers
The three primary nutrients plants need to grow are nitrogen, phosphorus, and potassium (the “K” is the chemical symbol for potassium). Fertilizer products provide N-P-K ratio numbers to indicate the three nutrients contained in the product.
In general, look for a fertilizer labeled for use with vegetables.
Fertilizer Safety
Use only fertilizers sold for gardens. Lawn fertilizers usually contain too much nitrogen and/or weed control chemicals that can harm vegetables.
Plant fertilizers can be harmful to children if swallowed. Touching a large amount of plant fertilizer may cause skin burns. Carefully supervise students when using fertilizers and use judgment and caution when letting older students apply the fertilizers. Store all chemicals safely out of students’ reach.
“Plant Food” vs. Fertilizer
Technically, “plant food” refers to the chemicals that plants need and use to grow. Fertilization is the application of fertilizer in the soil and around the plant that contains the chemical elements plants need. Fertilizers make the soil more “fertile,” or capable of bearing more productive, “fruitful” plants.
Types of Fertilizers
Granular slow-release fertilizer is a solid fertilizer that dissolves over days to slowly make nutrients available to plants through the soil over a period of time. Slow-release fertilizers are generally spread directly onto the soil and gently worked down into the top few inches or added to the planting hole during transplanting.
Water soluble fertilizer is usually in the form of granules that dissolve in water and allow for the rapid uptake of nutrients. Some water soluble fertilizers are sold as concentrated liquids. Follow the package instructions to measure out the granule or concentrated liquid and mix with water. Then, you simply apply the water to your garden beds as described above. The nutrients in the fertilizer will be in solution, so they are available to plants faster than granular fertilizer. Since they are water soluble, they persist in the soil for a shorter time.
Both types of fertilizers can be affected by heavy rainfall or irrigation and be leached out of the soil faster as a result. You may need to re-fertilize if that occurs.
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