Whist I have been down south at Badminton Horse Trials, my horse has been moved from the hardstanding into the summer field. Meanwhile, this means I have less hay nets to fill, there are some key things you need to watch out for when your horse goes into a summer field.
Firstly, laminitis, many horses will go out onto grass for the first time in 6+ months and they will eat as much as they can, which may result in laminitis. I would recommend splitting your field with electric tape so that you are limiting the amount of grass your horse can access. I would initially also put your horse out for no longer than 3 hours this way you are preventing them from gorging themselves on the grass.
Secondly, energy, my advice when you go to ride your horse for the first time since they have been on grass is to have someone with you. As at this time of the year when spring is in the air horses tend to become a bit full of themselves and a bit hyper. Speaking from experience it is likely that your horse will either protest to being ridden or will have a moment of eruption, which usually results in the rider ending up on the deck.
Finally, flies! Now that we are coming into the nicer weather it is important to protect your horse from flies. Fly spray and fly sheets/masks can be bought from most equestrian stores, if not online.
It is also important to monitor how much your horse is eating and drinking during warm weather to prevent them from getting dehydrated. I therefore do not recommend automatic water feeders as this means you cannot monitor how much your horse is drinking. Although it is harder work, I recommend filling a bucket of fresh water each day and putting it in the field when your horse is out. This means you can monitor how much they are drinking.