Harish,
Temps above 40 degrees F. will cause the figs to break dormancy. At 50-55 degrees F. the dormant buds will begin swelling and growth will start. You don't want this to happen. You only want dormancy to stop when it is warm enough outside for them to commence active growth outside.
Your unheated greenhouse seems to be the best option. You could, if the light in it is good, give the figs an early start for the growing season, and then put them outside when all frosts are past. You will in this way, get an earlier ripe crop, every container fig gardener's dream.....all figs ripening before the first fall frosts.
Once the figs have broken dormancy they need full sun and no lows below freezing. Figs are very sensitive to frost.
Mission is my favorite so far. Your two Missions (lucky you!), LSU Purple, and Olympian are great choices. I also have the three you have, and 17 other different varieties. I am experimenting to see: the tastiest, most prolific, easy to grow, etc. It will take a number of years....that's the fun of it.
I have about 70 figs (14 figs last year), on my Mission right now. It is in its 4th. year, 2017. It was a 6" rooted cutting its first year, 2014. Lots of branches and only 2.5' tall right now. Still a very young tree, being kept short and stout purposely. Unfortunately, it has Fig Mosaic Virus, came with it, but is growing strong and vigorously. Avoid virused figs. They can do very well, but better not to have any, if at all possible.
I do tip pruning when spring shoots are at the 6-7 leaf stage. This hastens fig formation to insure early ripening. Pinch the tip when the 6th to 7th. leaf is about 1/3 its fully extended length. Wait until it gets to that size. Go by the fully extended older, lower leaves on that stem for size comparison. This gives bigger figs over against pinching the tip earlier in its development when the new growing tip leaves are tiny. This is a new growing hint I learned this year. You're always learning.
Figs need plenty of sunshine, heat, and water.
No tip pinching past 4th. Of July. Any figs that start developing on stems after 4th. Of July, will not ripen in time. It takes 90-120 days for a fig to fully ripen from when it just starts to form at the size of a mustard seed at the base of a leaf. Late developers are just wasted figs and wasted energy. You want to see all your baby fruits, figlets, start developing at leaf bases before and up to The 4th. Of July.
Give Celeste, Conadria, LSU Gold, and little Miss Figgy a try. They are precocious fruiters. Experiment with as many different varieties that you can handle. That's the only way you can find out what is best for you.
Fertilizer needs are simple. May I recommend the Miracle Grow Shake n' Feed 3 month pellets for Roses and Blooms (new formula with microbes and worm castings), 10-18-9. Put it down once in April, then again in July. The N-P-K ratio is ideal for figs even though the label says for roses and blooms. Apply 4 oz. of non-burning lime every spring per 10 gallon fig, sprinkled on soil, watered in.
You can add Azomite dust, I do. I highly recommend it. It is full of trace minerals which maximize tree performance and fruit flavor. One rounded Tbl. per fig tree with each three month miracle grow feeding. Just sprinkle on top of soil.
Good, fast draining potting soil. Do not use the moisture retentive, polymer additive potting mixes. They can be root rotters, killer soil!
Wide pots are critical for stability when the wind blows. You don't want your trees being knocked over with trunks/branches snapping off in strong winds. Lash fig trees to each other with rope and broom sticks to prevent wind tippling them over if that's a problem.
The black plastic nursery pots work best, IMHO. Cheap, sturdy, stable. Stick to no more than 10 gal. size. Your back will thank you. Root pruning and branch pruning are the name of the game with figs. They take root pruning and top pruning in stride.....like no other plants I know. Keep them short (4-5' max.), and wide, for easy of handling and stability.
Multiple trunks are better than single. Keep branching low and compact, but not crowded....keeps center of gravity low so the tree does not topple over easily. I cannot emphasize how disheartening it is to have a tall potted fig get knocked over in a strong wind and snap in half.
Fig leaves are big and act like sails in the wind, catching the wind easily.
You can, in New Jersey, keep a fig that gets 20' tall in the ground in South Texas, grow 4-5' tall with good pruning, and be very productive and happy in a 10 gal. pot.
So long for now.
Moses
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Fertilizer by Moses.
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