Container plantings and pots will need the most attention during holidays. If you’re gone just a few days, you can just move them out of the sun into a shady site, or even a cool garage. They’ll lose much less water there.
If you know early in the season when planting, that you may be taking a holiday later, put into the potting mix some water absorbing gels. These especially are great in hanging baskets, even if you aren’t going on holiday. They absorb water, releasing it to the mix as it dries. Keep in mind too that clay pots will dry out much quicker than plastic ones. Another option is to plant into self-watering containers. These are especially popular with houseplants. They often consist of a pot with a false bottom, to which water is added, and that wicks up into the soil through a fabric of some sort.
In the garden, watering well before you leave may last a week, depending on the weather. It’s best to start watering early in the season, deeply and less often. This will “train” the plants to not need water daily, the roots going deeper and not growing just near the surface. If you have lots of plants and gardens, too many to all water if it doesn’t rain, just focus on the new plantings this year, vegetables, and more special (or expensive) trees and shrubs. Even a couple inches of organic mulch, such as bark or pine needles, and straw in the vegetable garden, will help conserve moisture and slow down weeds from coming up.
If you’ll be gone for longer periods, or holiday more often, you may want to invest in an automatic watering system. An inexpensive alternative are soaker hoses made of recycled materials. Water slowly seeps out of these hoses that you lay throughout the beds, or along garden rows under mulch. You can have a house sitter turn these on as directed or needed, or you can put these on timers. The timers are relatively inexpensive devices, found at many home and garden shops that you put on the faucet and then attach to the hose.
You’ll want to plan a few weeks out to make sure your beds are weeded, otherwise these will take up water your plants need, will create competitive stress for them, and may be hard to get under control once you’re home again. Then check plants a couple days before leaving to make sure no pests, and treat if so.
In addition to watering, you’ll want to make sure your lawn is mowed before leaving. This may last a week or 10 days, depending on weather. You don’t want to mow extra low, as this will only stress the grass. It is better to have it be high when you return, then mow once again and again lower in a few days.
Look after your herbs
If you have herbs, pinch flowers off so new growth will develop. If they’re ready to harvest, do so and dry while you’re away. Pick any produce from the garden or fruits that are ripe, or that can continue to ripen once picked. Otherwise they can get too large, lose flavour, rot, fall off, and cause disease.
Don’t plant within a month or so before going on holiday, so you’ll be around to water and tend the plantings until they become somewhat established. Don’t fertilise annuals just before leaving, as this will just stimulate new growth that needs more water.