A gardening expert has revealed the exact time frame that is best for watering your roses to make sure they enjoy healthy growth and bloom fully in time for summer. Louise Harrow has spent over 20 years designing and maintaining residential and RHS-standard gardens and has advised gardeners when they should be watering their roses. According to Harrow, the best time to water your roses in the UK is between 6am and 9am. 

She says that it isn't just how you water your flowers that affects how they grow. It is also when you water them. Not only is this important for flowers, but she says that the morning time is especially crucial if you are growing vegetables in your garden. These, along with potted plants are more vulnerable to heat stress. The temperature in the morning time, when the sun is yet to be high in the sky, is when roses will get the most benefit from watering. 

Harrow explains: "The optimal time is between 6am and 9am—when temperatures are still cool, the sun is low, and plants are just starting to ‘wake up’ for the day."

There are a number of scientific reasons for this, the first one being lower rates of evaporation. Spring and summer morning temperatures in the UK are usually between 10C and 15C. As this is much cooler than the middle of the day, the chance of water evaporating is far lower. 

Secondly, it lead to healthier roots. This is because cooler water gets to the roots of the plant before the heat arrives, therefore helping the plant and its roots stay hydrated throughout the day. 

Watering roses earlier in the day is also important for reducing the chance of disease. Harrow says: "Watering in the morning means leaves dry out faster, reducing the risk of mildew, root rot, and fungal infections."

If you have missed this morning window, then it is not the end of the world. Harrow also says that the evening time, although not ideal, is the second-best option for when you want to water your roses. 

She explains: "Water between 6pm and 7:30pm if you must. Temperatures have dropped slightly by then—usually to 16–18°C in summer—and there's still time for leaves to dry before nightfall."

However, there is a risk involved in this. Harrow says: "If the air is still and the garden gets no breeze, moisture will cling to foliage overnight—that’s a breeding ground for disease."

The worst time to water your roses and other plants, she says, is between 10am and 4pm when up to 40 percent of the water can be lost to evaporation when temperatures are higher.