How to Irrigate Vegetable Beds with Drip Tubing

Q. 1) what should the watering times be for Vegetable beds planted with typical vegetable seeds at this time of year?

2) Should the length of time be different when the beds are first seeded, as opposed to a month later when there are plants growing?

3) How should those times change seasonally with the temperature changes, that is, spring, summer, fall and winter?

A. Those are great questions and thank you for asking them. I hope that you will take my suggestions as just suggestions, and not as the "gospel". It's better if you use these as starting points and adjust my advice to fit your needs. I use 1/2 inch drip tubing with the emitters embedded into the walls of the tubing every 12 inches. I use 1 gallon per hour emitters. 

When installing this drip tubing, I make sure that the neighboring irrigation emitters offset the neighboring emitters by 6 inches. In other words, the emitters are spaced from each other in a diamond or triangular pattern.

Drip tubing with embedded drip emitters every 12 inches and spaced in a diamond or triangular pattern on a raised bed without permanent sidewalls

Let me go through a list of general rules that I use and let's go from there.

I soak large seed such as corn, peas, beans and even garlic cloves in tepid water for several hours before I plant it. The first step in seed germination is the uptake or imbibition of water. Doing this can speed up germination and reduce it by two or more days. Otherwise, you have to keep the soil constantly wet and can be nearly impossible for seed germination when air temperature gets above 90° F.

 

Raised vegetable bed mulched after seeding and irrigated using drip tape.

I mulch the area where seed is sown with a 1/2 inch layer to help keep the soil and seed wet. I have tried a number of different mulches including sand, straw, compost, perlite, vermiculite, and peat moss and found that bedding used for horses (pine shavings) to be the best. These thin shavings "dissolve" into the soil over several weeks while straw does not and can sometimes interfere with soil preparation. This can be bought at Viragrow (www.viragrow.com) or any farm supply stores. 

Seedlings mulched with horse bedding, pine shavings, to help preserve a soil moisture after seeding and seedling emergence.

I work with 12 inch spacing so the number of minutes of run time may be shorter or longer for spacing different from this. The number of minutes should be long enough to get water the entire 12 inch depth each time you water. Use a soil moisture meter (like for houseplants) to see how deep it goes.

 

Houseplant moisture meter used to gauge the depth of watering.

Surface mulch helps when starting plants from seed in containers.

1) what should the watering times be for beds planted with typical vegetable seeds at this time of year?

Make sure the seeds are planted the proper depth and it's best if they are covered with a 1/2 inch layer of horse bedding/mulch. If it is, you can water daily for 30 minutes. If you don't cover it with mulch, small seeds planted shallow, water three times a day for 15 minutes each. Large seed, 1 to 2 times per day for 15 minutes. It's easier with mulch. After the seeds germinate and you see their first true leaves, switch to once per day.

Seedling emergence through the surface mulch. Drip tape used for irrigation.

2) And, should the  length of time be different when the beds are first seeded, as opposed to a month later when there are plants growing?

A month later you could be watering once a day at 8:53 AM just before it starts to get warm. You want the plants to have access to water before he gets warm or windy. If these are smaller plants, water them for 30 minutes. If these are large plants, water them for 60 minutes. The progression of watering is from frequent, shallow irrigations after seeding or transplanting to deeper more widely spaced irrigations as they get more mature and bigger.

3) How should those times change seasonally with the temperature changes, that is, spring, summer, fall and winter?

Plant water use increases by 400% from the first month, January to the sixth and seventh months, June and July, in Las Vegas Nevada. Inches of water per day.

Water use in December and January is about 1/10 of an inch per day. In June and July it is about 4/10’s of an inch per day, a 400% increase. The change is in the frequency water is applied, not necessarily the number of minutes. So, after germination and establishment the water might be on for 60 minutes in December, the same amount in July. The difference is that watering in December might be every four days while in July it is daily.

Mulch, as I described above, really helps a lot when temperatures get above 90° F. You will see a difference in the plants when mulch is applied to the soil surface. Pine shavings such as horse bedding disappears in about 2 to 3 months and needs to be renewed.

With mulch applied, daily irrigations are enough during the middle of summer. If no mulch is applied, you will probably have to irrigate twice a day; once in the morning For 60 minutes and a second one midafternoon for another 60 minutes. These irrigations will be different if these raised beds were not amended each year with fresh compost. Amending them each year keeps the pore spaces in the soils open and plant roots will grow deeper. Plants with deep roots are less likely to become stressed during the heat.

Moisture meters like this one for houseplants are very inexpensive and not very accurate, but accurate enough to gauge if a soil is wet, moist or dry. The moisture sensor is in the tip so this tip should be pushed deep enough in the soil to be in about the middle of where the roots are growing. After an irrigation the meter will read "WET". Water again when the meter reads smack dab in the center of "MOIST". Use the "DRY' side to tell you when to irrigate cacti and succulents again.

I coach people into using a soil moisture meter when they first start learning how to irrigate. After an irrigation, the moisture meter should be pegged all the way to the right….WET. Irrigate again when the meter at root depth is halfway to dry (smack dab in the middle of the meter,….MOIST)