A few tips to help with your planter watering:
Know Your Plants - Most plants prefer to live in moist soil--not wet and soggy, just damp. Fortunately with modern potting mixes which are designed for good drainage, this is easier than it used to be. Some plants like to be dry, some like to have a dry period between watering, some like to be moist and then you have those fussy plants if they get just a tad dry, they will soon drop their buds and leaves. Different plants require different watering schedules. Succulents tend to like a drier soil. Flowering plants don’t like to get too dry. And vegetables, especially the juicy ones, like to be kept moist and need more water. Herbs tend to like that drying out period between watering. And other herbs, such as parsley, chives, sage, prefer a more moist soil.
Water Deeply - Most plant roots grow to the bottom of the planter they are in. It’s important to give your plants a good, long drink of water. Making sure the water makes it to the bottom of the plant, as the roots will grow down to the bottom. So watering until water runs out the drainage holes in your planter, will insure that you are getting water to the bottom of your plant.
Check Moisture Level – The top of the soil in your planter may look and feel dry. To be sure, stick your finger into the soil, a couple of inches. If it’s moist, then there is no need to water. If it’s dry, then it’s time to water.
Water the Soil, Not the Leaves – Wet leaves not only cause fungus, mildew and other diseases, but wet leaves can also burn the plant. Water on the leaves acts as a magnifying glass. So water the soil, not the plant.
Water in the Morning – This is the best time to water. Watering in the evening, especially if a plant gets wet, can increase disease, fungus and mildew as mentioned above, as the leaves are left wet all night long. Watering in the heat of the day, mid day, is NOT recommended either.
Don't Rely on the Rain – A plant can deter rain water, as it can act like an umbrella, sending the water around the plant and not reaching the plants roots. To be sure, check your soil below the plant, to be sure it’s moist.
Don't Assume Once is Enough – Pots, whether a hanging basket with coir, terra cotta or metal, heat, wind and dry air can quickly dry out and parch your plants. So you may need to water these more often. During the season, you will learn which pots/plants need more water.
Don't Let Soil Dry Out Completely – Most potting soils can become tough and don’t absorb water efficiently, causing the water to just run through and out the bottom. Leaving most of the soil still dry. This happens when you don’t water when needed and the soil just dries right up. Also soils that are left to dry out can cause your potting mix to pull away from the sides. Again, allowing the water to just run down and out the bottom. If you do let your soil dry out, you have a couple of options. If your pot is relatively small, you can take the whole thing and submerge it in a larger container of water, taking it out when it has stopped bubbling. For a large pot or one that is difficult to move, poke holes in the soil with a pencil or skewer, and then give it a good drink, making sure the water is penetrating the soil and not just flowing down the sides.
Most potting mixes become tough and won't absorb water efficiently if you let them completely dry out. Your potting mix can also pull away from the sides of your containers when it gets too dry, so while you may think you are giving your plant a good drink of water, the water may be just flowing over the soil, going down the sides of the pot and out the bottom, leaving your plant gasping for a drink.