Tag Archives: weather

Out in the Garden

When to turn on the irrigation?

by Steve Reiners, Professor, Horticulture, Cornell University, Cornell AgriTech

Water streaming down onto plantsThis spring has gone from dry to wet and back to dry, which can be frustrating for growers.  If you have been able to get your fields planted, it can sometimes be confusing in terms of when to water and for how long.

As soon as seeds germinate and plants break through the soil surface, it’s time to water more deeply.  Same is true after transplanting.  Shallow watering encourages shallow rooting and makes the plants more vulnerable to drought .

Deep watering will encourage roots to “follow the water” leading to deeper roots and more productive plants.  To sum up your basic watering strategy:  Water less often, but longer when you do.

If growing outdoors, it’s easy enough to keep a water budget.  At this time of the year, apply at least 1/3 of an inch of water at least two to three times per week if it doesn’t rain.  As plants grow and temperatures warm, increase the watering to 1/3 of an inch three to four times per week.  Keep a rain gauge in your field and measure your rainfall.

hand trowel in soilYou can also ‘feel’ your soil to see when it may be time to water.  Pick some up and try rolling it into a ball.  If you can, the soil is moist enough.  Or put your finger in the soil or dig down with a hand trowel.  Is it dry more than two inches deep?  Then it’s time to water.

Some commercial growers will purchase equipment like tensiometers which estimates soil moisture at various depths.  When a certain level of dryness is reached, irrigation starts.

If water access is limited, look at the chart below to determine the critical time to water a particular crop.  Focus your irrigation efforts on crops in these stages.

Table 1. Critical irrigation periods for vegetable crops

Crop Critical Stage for moisture stress
Asparagus Fern growth
Beans Flowering, Pod fill
Broccoli, Cabbage, Cauliflower Establishment and head filling
Carrot Establishment and root development
Cucumber, melon, pumpkin, squash Flowering and fruit enlargement
Eggplant Flowering and fruit development
Lettuce Head development
Onion Bulb enlargement
Pea Flowering, Pod fill
Pepper Transplanting, fruit set and development
Sweet Corn Tassel, silk, ear fill
Tomato Flowering, fruit set, enlargement

An inch of water on an acre is a lot of gallons – 27,000 to be exact. So, if watering only with a third of an inch you need 9,000 gallons. On a smaller scale, a 100 square foot garden requires 70 gallons for one inch of water.

Oscillating Sprinkler watering a gardenOverhead irrigation is easy to use and can water large areas at one time. Unfortunately, it also wets the leaves.  And as any plant pathologist will tell you, wet leaves equal disease.  Pathogens spread easily when plants are wet.  So, if you can, water in the morning so that leaves can dry through the day.  Watering in the evening assures a long period of leaf wetness, practically guaranteeing disease.

Drip Irrigation in a garden bed
Drip irrigation system

Trickle or drip irrigation is an effective alternative to overhead irrigation.  These systems apply water  slowly  through perforated tubes laid directly on the soil, which decreases the amount of water needed by 50 percent or more.  Little water is lost to evaporation as it is uniformly applied slowly right at the roots.    Leaves remain dry, diseases are reduced, and you can water at any time, day or night, whatever fits your schedule.  You can even water while working in the garden.

Out in the Garden, Vegetable Gardening

Patience is a Virtue in Planting Outdoors

by Joyce Tomaselli, Community Horticulture Educator, Cornell Cooperative Extension Dutchess County

A version of this article appeared in the Times Herald-Record in May of 2017.

Tray of cabbage seedlingsMany sources provide great advice on sowing seeds.  Key factors include sufficient light and temperature for growing the seeds.  But the question inevitably arises when to transplant them outdoors. Don’t rush.  Cold soil and air temperatures can stress plants.  Wait at least a week or two after the last frost.

The latest map from the National  Oceanic and Atmospheric Administration (NOAA) shows the last spring frost date for the Hudson Valley to be between New York, which indicates April 16th and May 15th. But of course these dates are only guides.  In 2020 we had a hard frost on May 15th that severely damaged many plants.  There is no guarantee that frost will not occur after the last date shown.  This map does not tell you the best time to plant tomatoes or other frost-sensitive crops. That date is usually several weeks after the last frost, after the soil has warmed and nighttime temperatures are reliably well above freezing.

  • Map of the showing soil temperature in the nOrtheastern US on May 10, 2021Nighttime temperatures should be consistently above 45°F, and the soil should be warm, about 70°F.  You can use black plastic mulch to warm soil and/or row covers, hot caps or other protection to keep plants warm early in the season. Remove covers whenever temperatures exceed 85°F.
  • Harden off plants before transplanting by reducing water and fertilizer, not by exposing to cold temperatures, which can stress them and stunt growth.
  • Remember that microclimates have a tremendous effect. Some valleys and low-lying areas can be plagued by late frosts on clear, cold nights when there is radiational cooling.  Large bodies of water (such as the Hudson) may moderate air temperatures at some sites, reducing the chances of frost.

Since plant development is temperature-dependent, rather than depending on specific calendar dates we can make decisions based on Growing Degree Days, a measure of accumulated heat or by observing phenological events of plants.

A branch of forsythia in full blloom - yellow flowersPhenology is a branch of science that studies the relationships such as the life cycles of plants and animals and environmental changes. Seasonal changes such as weather or temperature can be correlated with natural events such as bird migration, plant budding, flowering or fruiting and insect activities.  For example, in the Hudson Valley migrating hummingbirds usually arrive when forsythia bloom. Centuries ago, Native Americans began planting corn when oak leaves are the size of a Snowdrop (Galanthus nivalis).

University of Wisconsin Extension has provided some examples of phenological correlations:

  • Dandelion with a bright yellow flower growing in the crack between two paversPlant peas when forsythia blooms.
  • Plant potatoes when the first dandelion blooms.
  • Plant beets, carrots, cole crops, lettuce and spinach when lilac is in first leaf.
  • Plant corn when oak leaves are the size of a squirrel’s ear.
  • Light purple lilac bloomsPlant bean, cucumber, and squash seeds when lilac is in full bloom.
  • Plant tomatoes when lily-of-the-valley plants are in full bloom.
  • Transplant eggplant, melons, and peppers when irises bloom.

So watch the calendar, but also watch for other clues from nature when you’re making decisions about planting and transplanting outdoors.