Water is the daily work of a flower garden, and it is the work that decides whether the garden looks lush or tired. A flower that is short of water stops flowering, drops its buds and wilts; a flower that is overwatered rots at the roots, yellows and dies. The difference between the two is not a schedule but a habit: look at the soil, water deeply at the roots, and let the soil dry a little before you water again. Learn that habit and most watering problems disappear.
Different flowers need different amounts of water, and the differences are worth knowing. Newly sown seed and newly planted young plants need water every day until they are established. Annuals such as petunias, zinnias and marigolds need regular water through the flowering season. Perennials such as peonies, lilies and hydrangeas need water while they are growing and flowering, and less once they are established. Bulbs such as tulips and daffodils need water in spring while they grow and flower, and almost none in summer, when they are dormant. Roses and dahlias are thirsty and need deep watering in dry weather. Lavender and other Mediterranean flowers need very little water once established, and they will rot if they are watered like a petunia.
The best way to judge whether to water is to look at the soil, not the calendar. Push a finger into the soil near the roots: if it is moist an inch down, wait; if it is dry, water deeply. A plant that wilts in the afternoon but recovers by morning is coping; a plant that is still wilted in the morning needs water now. If you are unsure about a variety, a spray, or a diagnosis, check your local extension service — its advice is matched to your climate and soil.
Deep watering: how flower roots actually drink
Flowers, like all plants, want a deep soaking that reaches the roots, followed by a drying period that lets the soil breathe. A light sprinkle only wets the surface, encouraging shallow roots and wet leaves, and it is the worst way to water a flower bed. Water slowly and deeply so the moisture soaks six to eight inches down for annuals and perennials, and deeper for roses and shrubs. A soaker hose or a drip line left running for an hour does this far better than a sprinkler held for five minutes. Water at the base of the plant, not over the leaves and flowers: wet foliage spreads fungal disease, wet flowers rot, and water on a rose in the evening is an invitation to black spot. Morning is the best time to water, because the leaves dry quickly and the plant has the whole day to use the water; evening watering leaves the plant damp overnight, which invites disease. The watering calculator can help you work out how much water your soil and climate call for.
How much water each flower needs
Petunias, geraniums, dahlias and hydrangeas are among the thirstiest flowers, and they need regular, deep watering through the flowering season — a hydrangea that is short of water wilts dramatically, and it is telling the truth. Roses need deep watering in dry weather, especially while they are flowering, and a rose that is short of water produces small, poor flowers. Zinnias, marigolds and cosmos need regular water but are more tolerant of a dry spell than petunias, and they will usually recover from a missed watering. Sunflowers need plenty of water while they are growing tall, and less once they are in flower. Lilies and peonies need water in spring while they grow and flower, and less in summer once they are established. Tulips and daffodils need water in spring and almost none in summer, when the bulb is dormant — watering a dormant bulb will rot it. Lavender, rosemary and other Mediterranean flowers need very little water once established, and they must have sharp drainage, because wet feet will kill them faster than drought.
Mulch: the easiest way to cut watering in half
A thick mulch is the single most effective thing you can do to reduce watering in a flower bed. Two or three inches of bark, compost or straw over the soil keeps it cool, holds moisture in, suppresses weeds that would steal the water, and feeds the soil as it breaks down. Bark suits roses, hydrangeas and perennials; compost suits annuals and beds that are replanted each year; gravel suits lavender and Mediterranean flowers, because it keeps the crown dry and reflects heat. Keep the mulch a few inches away from the stems and the crown, because mulch piled against a stem holds moisture against it and invites rot. Renew the mulch each spring, and check the soil under it before watering: mulched soil stays moist far longer than bare soil, and overwatering a mulched bed is a real risk. The mulch calculator can work out how much mulch a bed needs.
Watering through the seasons
In spring, water newly sown seed and newly planted young plants regularly, and water bulbs as they grow and flower, but established perennials in a wet spring may need no extra water at all. In summer, water is critical: this is when annuals flower, and a dry spell now stops the flowering and drops the buds. Water deeply once or twice a week in dry weather rather than a little every day, and water containers daily, or twice daily in a heatwave. In autumn, ease off as the flowering finishes and the plants prepare for dormancy, but do not let a newly planted perennial go into winter drought-stressed — a deep watering before the ground freezes helps it survive. In winter, outdoor flowers need almost no water, but container flowers and flowers in a greenhouse still need occasional watering on mild days, because pots dry out even in winter. Newly planted flowers need watering through their first full season, in every month except when the ground is frozen.
Watering containers, baskets and window boxes
Container flowers dry out far faster than flowers in the ground, and a hanging basket is the fastest of all. Water containers daily in summer, and twice daily in a heatwave, watering until it runs from the drainage holes. A basket lined with a moisture-retentive liner, a pot grouped with other pots so they shade each other's sides, and a mulch on the surface will all slow drying. Self-watering pots and drip irrigation on a timer are worth the investment if you travel, because one missed watering on a hot day can finish a basket. Window boxes dry out fast too, because they are shallow and exposed, and they need the same daily attention. In winter, water containers sparingly, just enough to keep the compost from drying out completely. The watering schedule generator can help you set a routine for containers in your climate.
Watering mistakes and how to fix them
The most common mistake is watering a little every day, which keeps the surface wet and the roots shallow, and encourages fungal disease. The second is watering the leaves instead of the soil, which spreads black spot, powdery mildew and grey mould. The third is forgetting containers, which can go from moist to bone dry in a single hot day. Signs of underwatering are wilting that does not recover overnight, buds dropping before they open, leaf edges browning, and flowering stopping. Signs of overwatering are yellowing leaves, wilting in wet soil, and a sour smell from the soil — if the soil smells sour, the roots are starved of air and you should stop watering, improve the drainage, and let the soil dry out before watering again. A flower that has been overwatered will not recover by being watered more, and a flower that is wilting in wet soil needs drainage, not water. When in doubt, check the soil with your finger before reaching for the watering can.
Frequently asked questions
How often should I water my flowers?
Water deeply once or twice a week in dry weather, and less when it rains. New plants need water daily until established, and containers need water daily in summer.
Is it better to water flowers in the morning or evening?
Morning is best. The plant uses the water through the day and the leaves dry quickly, which reduces disease. Evening watering leaves foliage damp overnight.
Why are my flower buds dropping before they open?
Usually underwatering, a sudden change in temperature, or dry air indoors. Water deeply, keep conditions steady, and the plant will usually set new buds.
How much water do roses need?
Roses are thirsty and need deep watering in dry weather, especially while flowering. Water at the base, in the morning, and mulch to hold moisture in.
Can I overwater flowers?
Yes, easily. Roots need air as well as water, and soil that stays waterlogged will rot the roots. Water deeply, then let the soil dry out before watering again, and never water if the soil is already moist.
Good flower watering is a habit, not a formula: check the soil, water deeply at the roots, mulch well, and water containers daily in summer. Set up a soaker hose if you can, and keep a note of when you water and how the plants respond. For the water needs of individual flowers, see the growing guides, including roses and dahlias, and use the watering calculator to plan a routine for your garden.