wanted: watering advice

Over a week has passed since I planted my raised bed. The plants seem to be doing well, still no sprouts from the seeds however. I'm confident that the plants are receiving enough sun and I'm still giving my new soil the benefit of the doubt. That means that water is my primary concern. Obviously plants need water. But why?

Curious about the chemistry of water's role in photosynthesis, I dusted off my college biology textbook and refreshed my memory. Photosynthesis is the process of converting solar energy into chemical energy that can be used by plants. The primary byproduct of photosynthesis are carbohydrates (chains of carbon) such as glucose or fructose.

These carbohydrates store energy for the plant. To make a carbohydrate, the plant needs high energy electrons to connect the carbon atoms together. Where do these electrons come from? When a photon (a packet of light energy) hits the pigment molecule in the leaf, the photon causes one of the pigment's electrons to become a high energy electron. This high energy electron is then used by the plant to create carbon chains. But what about the water? Since the pigment is a donor of electrons, those electrons need to be replenished. Water supplies new low energy electrons to the pigment once the water molecule itself has been split by a photon (photolysis):

Oxygen is a byproduct of photolysis and it is released by the plant into the atmosphere. The hydrogen atoms are also used by the plant to create the carbohydrate sugars.

In addition to the role water plays as an electron replenisher in photosynthesis, water is also important as a solvent to transport minerals and carbohydrates throughout the plant. Water also helps cool the plant as it evaporates through openings (called stomata) in the plant leaves.

So clearly, I need to make sure I give my plants the water they need. But how much? How often? And what time of day?

I posted these questions on the vegetable garden forum (GardenWeb) and received the following responses:

• "One thing that I do know is that some say it is better to water in the evening (probably after 6pm for you), so you avoid any issues with the water burning onto the plants."

• "Don't believe any of that nonsense about water droplets in the sun burning the plants in the sun. It's much worse to have your plants wet all night long. Your plants prefer their leaves to be dry as much as possible. I'll water any time at all if I avoid getting the leaves wet, which is better still. Whenever practical, water the roots, not the leaves. Some would say early morning is best cuz it's cool enough that the water will soak in nicely before evaporating, and they have a point. I kinda like watering just before dusk, soil only, so the roots have all night long to leisurely soak up what they need. And evaporation is minimized."

• "I like to water in the morning so the plants can take up the water and not droop in the heat of the day. Always water at the soil level, never on the leaves."

• "Watering deeply in the morning is preferred here. If you overhead water, each drop can act as a prism and burn a leaf. Also, you want the roots to get the moisture, not the leaves."

• "Watering in the morning is much better, and only at the stems/roots. BTW, you have a very nice city to live in - I visited in April, and drove to the university football stadium for a photo opportunity - If I wouldn't have known which street it was on , i'd never have found it! OMG, it's hidden behind trees and foliage.Anyway - very nice place to visit."

• "Once plants are established, think in terms of water conservation and plant vigor. If you water too much, your plants will not develop the vigor they need to be extremely productive, among other things. And conservation means deep root watering during the coolest times of the day to prevent evaporation. Early morning is considered the optimum time to make the most of your water with a mind towards conservation."

Based on the somewhat conflicting advice I received, I decided to try watering in the mornings, before the sun reached my bed. I also took the spray nozzle off of the hose and put the end of the hose at the base of each plant for a few minutes to avoid watering the leaves. This allows the water to actually seep into the soil, instead of running down the hardened surface of the bed. Hopefully this method will yield healthy, well-watered plants! Many thanks to water for supplying those low-energy electrons!