There is no need to be worried about leaving your houseplants while you travel. There are several ways to ensure they receive the watering they need while you're gone.
The good news is that most plants will be fine for 3-4 days as long as they are well watered before you leave. For trips that are longer than 4 days, you'll need to implement some other strategies.
Indoor houseplants should be moved away from sunny windows and out of hot rooms. This way they will use less water and can go longer between watering. Any outdoor houseplants should be moved to a shadier location so they don't dry out so quickly. A porch or cool garage is a good choice. Mulch around all the plants as this helps the soil retain moisture.
A wicking system is easy to set up and works especially well for those plants that can't be moved. Or, if you're like me, there are just too many plants to move! Wicking systems can be set-up indoors or outdoors. The basic concept is that an absorbent material will be arranged between a container of water and the plant. The material will absorb the water and draw it back to the plant.
You'll need containers, like pails, bowls, or bottles, to hold water and long strips of wicking material, like thick yarn, strips from a cotton t-shirt, or natural-fiber rope. Place the container of water next to the plant(s) and put the long strip of material in it so it reaches the bottom. Then, stick the other end of the wick about 3 inches into the plant's soil, making sure it won't fall out. Test the system before you leave to make sure the wick is moving the water to the plant.
Drip Watering System
Most gardening centers sell glass watering globes that can be inserted into the soil to provide water over an extended period of time. These work great and are a good investment. They are also easy to make yourself.
All you need is an empty and clean plastic water bottle. Drill several holes close to the top of the bottle. To use, fill it with water and press it upside down several inches into the soil. Do it quickly so the water doesn't spill! All the holes should be covered. As the soil dries out, the water will leak out of the bottle and water your plant.
A wine bottle can be used in place of a plastic bottle for bigger plants or to provide water for a longer time. You don't need to make holes in the glass bottle. Simply fill it with water and press the neck into the soil.
Bathtub/Sink Watering System
If you're going to be away for a week or less, the plants can be placed in a sink or bathtub. Before you leave, fill the bathtub or sink with several inches of water. Lay a towel across the bottom and arrange the plants on top of it. The plants will soak up the water as needed. The towel is there to protect the surface of the sink or tub; you can omit it if you like.
Find a Plant Sitter
If you have a large number of plants or are going to be gone for more than a couple weeks, it would be best to find a plant sitter to make sure all your plants receive the care they need. A plant sitter can be more attentive and specific about the watering schedule and how much each plant gets.
Book that vacation. Plan that trip. Your plants will be fine until you return as long as you set up a watering system for them. Happy traveling!