It is good to beware not to recite Shehechiyanu over new fruits during the three weeks [starting from the night of the 17th of Tammuz until after the 11th of Av]. This applies even if one already sees a new fruit, nevertheless, he is to delay the recital of Shehechiyanu until he eats it after the three weeks. [Accordingly, one is to avoid eating new fruits throughout the three weeks.]
If the fruit will no longer be available after the three weeks: A fruit which will no longer be available [i.e. not in season] after the ninth of Av [and cannot be guarded until then due to spoilage or loss of taste], may be eaten and have Shehechiyanu recited over it during the three weeks. [Those who say Shehechiyanu on Shabbos, are to wait until Shabbos to say it, unless the fruit will spoil by that time.]
Shehechiyanu on Shabbos: Some Poskim rule one may recite the blessing of Shehechiyanu over a new fruit on Shabbos [and Rosh Chodesh Menachem Av]. Other Poskim rule one may not recite Shehechiyanu even on Shabbos of the three weeks. [Other Poskim rule one may recite Shehechiyanu on Shabbos, up until the nine days.] Practically, the Chabad custom is to be stringent not to recite Shehechiyanu throughout the three weeks.
One is not to eat new fruits, and recite Shehechiyanu over them, throughout the three weeks, including Shabbos, unless the fruit will not be available afterwards.
If during the three weeks one said Shehechiyanu on a new fruit and prior to eating the fruit, realized his mistake, what is he to do?
One is to eat the new fruit, as the blessing as already made.
If one said a blessing of Haeitz over a new fruit, and then realized that the fruit is to receive a blessing of Shehechiyanu, what is he to do?
May a pregnant woman or sick person eat a new fruit if they have a craving for it?
May a child eat a new fruit and recite Shehechiyanu?
A child who is too young to understand the mourning period may be given a new fruit to eat and recite Shehechiyanu, if he is craving for the fruit.
When the 17th of Tammuz coincides with Shabbos, may one say Shehechiyanu that Shabbos?
Some Poskim rule it is permitted to say Shehechiyanu on that Shabbos even according to the stringent opinion. Others argue it is forbidden to do so according to the stringent opinion. On Friday night, some Poskim rule one may say Shehechiyanu according to all opinions.
 Chaim Sheol 1:24; Kaf Hachaim 551:207 unlike Mateh Efraim
 Machazik Bracha 558:3; Yosef Ometz 56; Shaareiy Teshuvah 558:2; Kaf Hachaim 551:208
 Michaber 551:17; Teshuvah Ashkenazim in name of Sefer Chassidim; Drashos Maharil Tisha B’av; Teshuvas Maharil 31; Agguda Brachos in name of Kolbo; Binyoman Zeev 163; Kneses Hagedola 551; Sefer Chassidim 840
Other Opinions: Some Poskim rule one may say Shehechiyanu during the three weeks on a fruit, as it is a Mitzvah, and by all Mitzvahs one is to do so as soon as possible, as one does not know when his time will come. [Taz 551:17; Yosef Katz of Krakow; See Machatzis Hashekel on M”A 551:44; Kaf Hachaim 551:220]
 M”A 551:43
 Sefer Chassidim 840; Rav Chaim Vital in Shaar Hakavanos; Birkeiy Yosef 551; Yosef Ometz 56; Maras Hayin 17; Mamar Mordechai 551:14; Zechor Leavraham 9 and 3:31; Shaareiy Teshuvah 551:38; Kaf Hachaim 551:204 and 207
Other opinions: Some Poskim rule one may eat the fruit without saying Shehechiyanu. [Beir Mayim Chaim 7; Kesones Yosef 11; See Birkeiy Yosef ibid in name of Mahariy Tzemach and Rav Chaim Vital that he ate a new fruit without Shehechiyanu]
 Rama ibid; Binyoman Zeev 163; Teshuvos Maharil
 M”A 551:44; Mizbeiach Adama; Machazik Bracha 551 Kuntrus Acharon ; Kaf Hachaim 551:218
 M”A 551:44; See Yad Efraim ibid
 Arizal in Shaar Hakavanos p. 89, brought in M”A 551:42; Mateh yehuda 551; Beis David 325; Tur Barkat , brought in Birkeiy Yosef 551:10; Chaim Sheol 1:24; Kaf Hachaim 551:205
 Beis Yehuda 61 p. 109; Glosses of Rebbe Akiva Eiger 551; Aruch Hashulchan 551:38; Shaar Hatziyon 551; Kaf Hachaim 551:205
 Mateh Moshe 697, and Levush brought in M”A 551:42; Taz 551:17; Sefer Chassidim 843; Kneses Hagedola 551; Elya Raba 551:42; Chayeh Adam 133:8; Derech Hachaim; Avnei Nezer 428; Kitzur SHU”A 122:2; M”B 551:98
 Aruch Hashulchan 551:38; Toras Chaim Sofer 551:35; Kinyan Torah 6:32
 Hayom Yom 21st Tammuz; Sefer Haminhagim;
 The issue is not with eating the new fruit, but with the Shehechiyanu, and the Shehechiyanu was already said.
 See Shaareiy Teshuvah 551:38; Kaf Hachaim 551:214
 Birkeiy Yosef 551:12 in name of Kneses Hagedola 2:34; Implication of Rav Chaim Vital in Shaar Hakavanos
 Birkeiy Yosef ibid in name of Mahariy Tzemach in name of Rav Chaim Vital, brought in Shaareiy Teshuvah 551:38; See Avnei Nezer 428; See Kaf Hachaim ibid
 Birkeiy Yosef 551:8 and 13; Mahariy Tzemach in Naggid Umitzvah p. 70 and Peri Eitz Chaim 23:1 regarding sick; Shaareiy Teshuvah 551:38; M”B 551:99; Kaf Hachaim 551:211
 Opinion in Birkeiy Yosef ibid; M”B 551:99; See Shaareiy Teshuvah and Kaf Hachaim ibid
 Birkeiy Yosef ibid in name of Kneses Hagedola; Kaf Hachaim ibid
 Birkeiy Yosef 551:9; Zechor Leavraham 3:31; Kaf Hachaim 551:212
 M”A 551:42, brought in Beir Heiytiv 551:38; Elya Raba 551:42; Ramaz brought in Birkei Yosef 551:11; Shaareiy Teshuvah 551:38
 Mor Uketzia 551; Birkeiy Yosef ibid in name of Kneses Hegdola 2:9; Chaim Sheal 1:24; Bigdei Yesha 551:42; Kaf Hachaim 551:206
 Sdei Chemed Bein Hametzarim 1:1; Nitei Gavriel p. 118