Summer will be every bit as busy as spring, but, due to increased skills and crafting knowledge, it will be less draining and be far more profitable.
Upgrade barn to Big then Deluxe and get a goat and pig!
Finish filling out the larger bundles (crab pot, exotic foraging, and artisan goods)!
Upgrade pick and axe to steel!
Get to level 80 in the mines!
Plant an apple tree!
Plant a Pomegranate tree!
Build Kegs!
Build lightning rods!
Grape
Spice Berry
Sweet Pea
Tomato
Hot Pepper
Blueberry
Melon
Corn
Gold star melon x 5
Gold Star Corn x 5
Sturgeon: 6am-7pm, all weather
Tuna: 6am-7pm, any weather
Red snapper: 6am-7pm, rain
Tilapia: 6am-2pm, any weather
Pufferfish: 12pm-4pm, sunny
Poppy
Fiddlehead fern (secret wood, need steel axe to clear log and access)
To start the month strong you should have cash to buy the following:
9 corn
9 Blueberry
9 Tomatoes
9 Hot Peppers
9 Hops
9 Radish
9 Melons
9 Wheat
8 Poppy (Ideal, 4 if money is tight)
9 Sunflower (Ideal, 4 if money is tight)
That's a great deal of money (7190g for the ideal, 5790g for the cheaper option with 4 of each flower), but once you have those plants down you should be set for the summer as most of them (corn, blueberry, tomatoes, peppers, and hops) produce all season, with corn going so far as to last Summer and Fall. Radish and Wheat are single growth, but nice cash crops, especially considering how cheap and fast wheat is. Melons are expensive and take a long time to grow, but they are high value, so try to keep a couple of patches of them going, especially considering you need 5 gold star melons for the quality bundle. I buy 9 at the start of the month but you should have 9 more available from Gunther as an archeology award and usually buy at least 9 more after the first harvest.
Crop placement is your option, you do want to keep things grouped up for your scarecrow and I like to keep them close to the water for convenience, but there are few firm rules, the ones I make for myself are:
Hops are blockers, they grow on a trellis and you can't walk through them so don't put them where you can't walk past, I like to put these against the property line in a continuous row. This row also sets a precedent for the rest of the patch.
For the summer I generally put most crops in rows as opposed to blocks, the Hops are easier to work with this way and I don't bother with sprinklers until I can make Quality Sprinklers (1 iron bar, 1 Gold bar, 1 refined quartz, farming level 6). I make an exception for wheat, radishes, a secondary melon patch, and the flowers, which I will explain.
Corn is dual season so I like to use the opposite edge of the garden to grow that, keeps it together, yet separate, and easily managed over the season change. This is mostly due to my need for order, but its what I do.
Flowers are put in blocks. If you have the money for the full package as listed above I put the sunflowers in their own block, keeps things ordered and separate when replanting; poppies are the same except I only plant 8 with a blank in the middle so I can put down a beehive. Once they've grown they can be left for the bees to extract honey. If I can only afford some of the flowers I put them all in one block, still leaving the center open for a beehive; the beehive does not need to be centralized, just in the region, but, y'know, OCD.
Wheat I put in a block of its own, its fast growing and is replanted often, and I hate swinging my scythe through the rest of my crops, doesn't hurt them, but it bugs me, so there it is.
Radishes, no reason to have them on there own other than expediency; putting the rest of the crops in rows together gives you 6 rows, I water 9 blocks at a time so having 2 grouped rows of 3 each lets me do 1 swing down, then one swing back up, with a water can refill at the bottom. Radishes are quicker growing and require replanting so it keeps things neat to have them in their own block.
Secondary melon patch is the same thing as radishes, keeps things ordered and I rarely grow a second set of melons in this spot so it again keeps things neat.
*One exception to the rules I will sometimes make is to plant 8 corn in a block of their own, putting the radishes in their place in the main garden, and leaving space for a sprinkler. This is actually the better way to handle it, the trick with this is to make sure you put the block in the right spot, keeping in mind your fall crops, so your OCD doesn't slowly murder you*
Again, the summer foraging bundle will produce a pack of seeds (30), plan according to what you have room for and the amount of work you can handle daily, they extra income will really help out when the harvest happens.
Midmonth brings the Summer Luau, not a real big event, but a great way to score points with the locals. If you kept a Gold Star Cauliflower bring that along and throw it in the soup, you get 120 friendship points with everyone. Quick note: you should be at 8 hearts with Haley by this time, try to get her the bouquet bought ahead of time so you can benefit from the points with her as well.
Get your axe upgraded to steel within the first week so you can enter the secret woods and get the Woodskip and fern out of the way
You should be able to make a beehive or two (40 wood,8 coal, 1 iron bar, 1 maple syrup, farming level 3) and put them along side the flowers you will plant, the honey is a great source of income and required for the artisan bundle. Sunflowers are good for this as well (They also make great gifts as Haley loves them), and give more seeds at each harvest, although you will need to plant at least 1 poppy in order to get the chef bundle done. Keep some flowers planted and bloomed at all times.
By now you should have a few preserve jars (50 wood,40 stone, 8 coal, farming level 4) working and hopefully some kegs (30 wood,1 copper bar, 1 iron bar, 1 oak resin, farming level 8) running, 6 of each is ideal, but whatever you can get going. They take time, but you need preserves and wine for the bundles, and are a great source of income, especially once your hops plants start producing. Level 4 farming for the jars should not be an issue, level 8 for the kegs might be slower, fully doable, but you may need to prioritize to time to hit that.
Lightning rods (1 iron bar,1 refined quartz, 5 bat wings, foraging level 6) are a huge bonus during the summer and fall. You'll need 10 bat wings for the Adventurer Bundle in the Boiler Room, but any others you have use to make rods, every storm give a battery pack for each rod and sell for 500g each. One thing to note, as they require foraging level 6 you may or may not be able to build them by the first summer storm, depends on your priority.
By the end of the second week your barn should be upgraded to a Big Barn (12000g, 450 wood, 200 stone) and a goat (4000g) purchased; I also recommend building a second cheese press but, as the goat only produces milk every 2 days, you can make do with 1 press. After 5 days your goat will start to producing milk, giving you access to cheese, goat cheese, Large Milk, and Large Goat Milk; this along with the large white and brown eggs will give you most of the Animal Bundle already, but make sure to keep an egg or two in reserve for the fried egg in the chefs bundle.
You'll want your pick upgraded to steel next, you need it to clear the boulders from the farm, but the rocks in the mines will also be getting tougher, you'll spend a lot of time clearing them to get through levels, time you don't have as you want to get to level 80 quickly in order to access gold for the fall.
Make sure you are getting your combat experience in the mines, depending on your drops, you may need to spend money on a new weapon, you need to be able to burn through these levels, and slow combat will seriously impact your success.
Make sure you are fishing early, some of these fish, like the Puffer and Sturgeon, are challenging catches, and are available for limited time; same goes for rainy day fish, there are fewer rainy days in the summer, you need to get the fish while its available. Protip, to speed up the puffer and sturgeon catches purchase some trout soup from Willy, its 250g, replenishes 100 energy and boosts your fishing skill for most of the rest of the day (if it works out well, you can catch the puffer then head to the lake to get a sturgeon on the one buff).
By the last week of summer you should be getting the Deluxe Barn (25000g, 550 wood, 300 stone) built and try to get your pig (16000g) purchased . You need the pig in order to get a truffle for the Chef's Bundle and since truffles are also valuable you may as well maximize the amount of time the pig has to find them; since it takes 10 days for a pig to start producing truffles, its good to have it ready going into the fall.
If you've managed to get deep enough in the mines you can start bringing home gold which will be super valuable going into the fall and hopefully you have the money set aside for another big layout of seeds like the beginning of summer, it will help.
If you've been keeping up in your relationships you should have some good friends and be able to gift Haley the mermaid pendant by now; you'll need to wait until you've expanded your house to actually buy it, but that will be soon.
On top of having seed money for fall, like you did in the spring for summer, you can also stock up on summer seeds, they will be usable when the greenhouse unlocks next month and will be worth big money. I like to put in renewables, like blueberries, tomatoes, and hops, plant once and forget about them! If you don't have the cash right now, no biggie, you can grab these at the winter market later in the year.
Finally, get your fruit trees (1 apple sapling (4000g) and 1 pomegranate sapling (6000g)) planted before the end of the month as they take 28 days to start producing and you will need 3 apples and at least 1 pomegranate to fill out the bundles. It has been my experience the fruit bats always yield the pomegranate to fill the bundles, but not always enough apples, so if I have to make a choice I would plant an apple tree first, but nothing wrong with getting some insurance if you have the cash to spare and plant both trees. If you do not get them planted by the 25 of summer you will not get 3 apples by the end of fall.
If you've been making and selling the tea saplings then you should be able to fully upgrade your barn and coop, buy all your animals, plus plant your trees well before the end of the month. Depending on how you want to push things, you might even be able to upgrade your house and be ready for the mermaid pendant on the first fall rain.
Pro tip: Make sure to at least buy Hops for your greenhouse, then prep to build twice as many kegs as you have plants; hops produce daily and the kegs take 1.5 days to produce Pale Ale, so, once your greenhouse is built and the hops start producing, you'll have a nice daily cash flow from your ale production.