Campus Crops: Watering Tips: Because it's simple, yet not that much, though it's not so complicated, well it looks like it is at first, but it's not THAT hard to get the twist, you know

For the layperson, watering plants means pouring water over plants. Unfortunately, there’s much more to it and some inexperimented gardeners learn it the hard way.

Watering is done as needed, although more frequently for younger plants. As plants mature, mulched or not, their roots will be able to reach water deeper in the soil, and their foliage (with some exceptions) will shade the soil and reduce evaporation.

In general, mature crops need 1 to 3 inches of water per week, although water needs vary with the weather and the stage of growth of the plant (during fruit production, most crops will prefer to avoid drought and will need more water than usual in order to produce quality fruits). Therefore, it may not be necessary to water every day (containers may escape this rule, as they can’t hold as much water as the soil garden).

1. How can I know when it’s time to water?

An easy way to figure out if plants need water is to stick one’s finger in the soil, as deep as possible. For seedlings, stick your finger quite close to the plant; for mature plants, anywhere under the canopy should do. If the soil is moist or wet about 3 inches deep (i.e. if the soil is moist 3 inches deep and deeper, not if only moist 3 inches at the surface), big plants should do fine; for seedlings or maturing root crops, the soil should be moist at least 2 inches deep.

The same method can be used to know if one has watered enough. After watering, the soil should be wet at least as deep as one can reach with a finger. Be careful: the soil surface can look wet even though the water has only penetrated 1 inch deep in the soil. Shallow watering stimulates shallow rooting, which can make the difference between life and death for some crops during long drought events.

For soil gardens, you can also refer to this soil appearance table (which assumes you know what type of soil you have, which is something you should know anyway!).

The weather is also a good indicator. If it’s been hot and/or dry for the last few days, watering is probably needed. If it’s been quite cold and/or humid and/or rainy, watering may wait a few more days or more, depending on other conditions.

2. When should I water?

Watering in the morning provides plants with enough water to last through the day, which may prevent wilting or other ill effects of hot/dry weather. This also allows water to dry during the day, reducing risks of disease. Avoid watering in the middle of the day, as most of the water gets lost by evaporation. If watering at the end of the day, make sure that the plants will have time to dry before the night, otherwise they could develop fungal diseases.

3. Am I watering too much or not enough?

When overwatered, plants that elongate continuously, like tomato and squash, will favor stem and leaf production over fruit production.

All plants will also show signs of wilting if under or overwatered. Temporary wilting can occur on hot and dry days, but wilting caused by long-term under/overwatering will persist even after the plants have been watered and/or cooled.

Other symptoms of over or underwatering include curling leaves, yellowing leaves, falling leaves, falling flowers, etc. Evaluate the moisture of the soil (look or feel) to determine if the cause is overwatering (wet soil, maybe moss or mushrooms growing) or underwatering (dry soil, cracked or crusted).

If you overwatered, don’t water until the soil has dried enough (use the finger technique). Overwatering can carry nutrients in the soil deeper than the plants' root depth and cause nutrient deficiencies.

If you underwatered, make sure that you don’t stop watering when the surface of the soil looks wet: use your finger to make sure the water penetrates well into the soil. Underwatering causes shallow rooting. This makes plants weaker and more susceptible to drought as they can’t reach the water and nutrients available in deeper layers of soil.

4. How should I water?

As much as possible, try to water awkwardly.

Too much water pressure can cause the soil to compact and crust, which in turn will make it harder for water to penetrate the soil. Try to simulate a gentle rain by adjusting the pressure, angle, or height of the water source.

You also want to avoid adding too much water at the same time, which can cause run off (i.e. displacement of soil). This is especially important when watering small seedlings or where seeds have just been planted, as you may uproot the seedlings, displace the seeds, or bury them, which prevents proper germination and growth.

Cold water cools the plants, reducing transpiration and plant temperature (plants stop growing when it’s too hot). Ice-cold water may, on the other hand, shock the plant and not be of any help. Warm water can be used in early spring and late fall, since the soil is cooler at that time.

Treated water contains chlorine, which kills beneficial micro-organisms in the soil and may also repel macro-organisms (insects and worms, e.g.). If possible, let the water sit in an open container for 24h before watering, for chlorine to evaporate.

5. Avoid wetting the leaves

Wet leaves develop diseases easily, particularly fungal diseases and especially if they stay wet overnight. When watering, try to only wet the soil.

6. Mulch

Mulch has many benefits, including reducing water loss by evaporation. Many types of mulches can be used, the most common being straw (not hay, as it includes weed seeds), dead leaves, grass cuttings, and woodchips. Woodchips should only be used for trees, fruit bushes, perennials, and large, mature fruiting plants (e.g. tomato after flowering).

It is also possible to reduce the use of mulch by planting crops densely with similar crops or with companion plants, but this may not be possible at the seedling stage and can pose challenges for nutrient management. Mulching fast-growing crops with high demands in nitrogen is generally not recommended, as the decomposition of the mulch will reduce the amount of nitrogen available to the crop and slow its growth.

7. Supplementary tips for outdoors irrigation

For soil gardens, fill glass or plastic bottles with water and plant them upside down at the base of your plants (be careful not to damage the roots!). The water will seep slowly into the soil as the plants need it.

And try to have fun, like this person does... No. No, that's too much, actually.

8. Watering and stage of growth

Plants are more sensitive to inadequate watering at some critical periods of development. If possible, according to the ‘rules’ of companion planting, those plants should be grouped together in the garden. For all crops, proper watering (no big fluctuations, no underwatering, no overwatering, no etc.) is essential during and 2-3 weeks before harvest, but some have other specific needs.

Vegetable: Critical period for water needs

Bean, lima: Pollination and pod development
Bean, snap: Pod enlargement
Broccoli: Head development
Cabbage Head: development
Carrot Root: enlargement
Cauliflower: Head development
Corn, sweet: Silking, tasseling, and ear development
Cucumber: Flowering and fruit development
Eggplant: Uniform supply from flowering through harvest
Melon: Fruit set and early development
Onion, dry: Bulb enlargement
Pea: Flowering and seed enlargement
Pepper: Uniform supply from flowering through harvest
Potato: Tuber set and tuber enlargement
Radish: Root enlargement
Squash: summer Bud development and flowering
Tomato: Uniform supply from flowering through harvest
Turnip: Root enlargement

Moisture fluctuation can also cause blossom end rot in tomatoes and fruit cracking in various fruits (including tomatoes) during fruit enlargement.