Watering Plants in Pots

Question from Donald:

I have my garden this year in 12/15 gallon pots and wonder if there is a simple way as when to water. I plan on using a watering sprinkling bucket. An due to our drought problems is why I went with pots and I don’t want to waste water. I have a moisture gauge and time to do it. Once, twice or more a week, need your input.

I have blackberries, tomatoes, peas, long beans, cucumbers, squash and onions.

Answer from Pat:

The amount of water used by your containers will be dependent on three main factors:

1. Potting soil. (Potting soil varies widely and sometimes the same brand varies from year to year or from batch to batch. Some potting soils drain well and retain adequate water for plant health. Some potting soils drain too rapidly and allow roots to dry out too quickly. Some potting soils drain too slowly or retain too much water which usually results in the plants doing poorly or dying of root rot. The latter category may contain a wetting agent.)

2. Climate: (Plants growing in interior regions will dry out sooner and need more water than plants growing along the coast. A plant growing on a hot patio with lots of reflected heat will need more irrigation than a plant growing in a cool location.)

3. Plant choice: (Plants with shallow roots may require more frequent watering than plants with deep roots. Most of the plants you have mentioned are deep-rooted but they may absorb moisture at different rates. For example, blackberries may require less frequent watering than cucumbers, which must be continually moist or they become bitter. Also globe onions, if that is what you are growing, require no water during the last two weeks of growth in late May or early June order to dry out the tops and cure the bulbs. However, scallions may require less water but more frequent irrigation than squash.)

Based on the above variations, here is what I suggest: Vegetables require one to two inches of rainfall or irrigation per week. In fast draining soils and hot weather they need more water. In slow-draining soils and coastal areas they need less. Therefore begin by giving one bucket of water to each container once a week and increase to twice a week watering as the weather warms up. Make sure that whenever you irrigate you apply enough irrigation that water runs out the bottom of the pot. When you grow plants in pots, this is one of the most important rules one must follow. So observe your plants and when they wilt be sure to water. Also stick your finger in the ground and see if the top 3 or 4 inches is dry. If so, it’s time to water.