I get a lot of questions from readers, and most of the time, the answers are fairly short. When I feel the question or the reply would be valuable to others as well, I make a post with a collection of them and post them in one go. Today is one of those posts.

"I would have a question about ancestor worship. As ancestors are chthonic beings, must they be sacrificed to outdoors by being poured libations onto the ground directly, or can they be worshipped  on an indoor altar and may the libations be poured into a libation vessel? If so, would it be appropriate to use the same one I use when I honor the ouranic theoi on my household altar?"

Ancestor worship was performed in Khthonic state festivals and as hero worship when at home. That is a generalization, of course, but it seems to mostly hold true.
There were regular state festivals organized for the dead (nekysia) and for the forefathers (genesia). On such days, graves were adorned, offerings of barley broth, milk, honey, unmixed wine, oil, water and the blood of animal sacrifices were given in the form of khoai--fully poured out libations. Graves often had bottomless amphorae placed on it on hollow columns. The libation was poured into this and seeped down into the dirt to 'feed the dead'.
The Genesia seems to have been a festival of the dead--especially of dead parents. It was celebrated on the fifth of the month of Boudromion in Athens, but that is all we know for sure. There is reason to believe that the Genesia was panhellenic--although we do not know if all city-states performed the rites on the same day. We are also unsure if the Genesia was a set day for all children to visit their parents' grave and perform sacrifices there, or if there was a public commemoration of all parents. The day is also sacred to Gaea, who housed the remains of the dead, and brought fertility and wealth to the living.
These rites were to commemorate specific people. It was also possible to honour the family line and it was actually a part of the celbration of Agathós Daímōn, the third day of the month. The goal was not to honour the people in the family line but to express pride in your blood and bring about good fortune as stemming from the family line. This type of worship was closer to hero worship and was performed at a separate shrine or at an offering pit outside. These sarcifices were generally wholely given as well and could either be an animal or, more commenly, unmixed wine.

"I am fortunate enough to live on a fairly large piece of property and while we have gardened in the past, this year we are making an effort to expand our gardening efforts quite a bit. I was wondering if it would be appropriate to make some sort of offering, possibly to Demeter, at the start of our planting season to ask for a plentiful harvest. Any suggestions you might have on how to go about this and which Theoi I should include would be greatly appreciated."

It is always appropriate to make offerings to the Theoi, at any time and for any reason. In fact, I greatly encourage it as this kharis will undoubtedly help with the growth and protection of your crops. The ancient Hellenic festival calendars always included and followed the cycle of achriculture. There were festivals for specific crops, like barley, but als grander festivals like those of the Eleusinian Mysteries that were celebrated to ensure a good harvest. The cycle started with the pre-ploughing festival Proerosia, continued into the Thesmophoria, then the Haloa. In general, fertility rituals were the domain of women and women only.
I assume every family practiced some sort of agricultural and fertility rite before plouging but we don't know exactly hat happened and who was sacrificed to. But, as always, we have clues because we know that what happened in state festivals usually also happened in private household worship, just at a smaller scale.
From this we can conclude that Gaea, Demeter, Kore and Dionysos were most likely the Theoi sacrificed to primarily. Gaea, as the earth, and Demeter as Goddess of the harvest make sense. Kore is the Goddess of growth, especially of new plants. Dionysos is also an agrarian deity as he is in charge of the growth of the grapevine. Then there are a few deities that come to me that I would definitely give sacrifice to before planting: the Hoirae as rulers of the seasons and weather, Helios as the Lord of the Sun (because you want enough of it but not too much) and Zeus Ombrios as Lord of the rain (because, again, you want enough of it but not too much).
Judging by the rites in the Eleusinian cycle, a pre-ploughing ritual may have had a symbolic (hand) ploughing of a portion of the soil. Onto this, barley groats would have been tossed as purification and sacrifice and copious libations of milk, honey and water would have been poured out in their entirety to the above mentioned Gods. Hymns and prayers would have been called up to the sky and prayers would have been said to ask for good growth, good weather and protection from crop diseases. In ancient times, an animal sacrifice might also have been a part of the rites.

"One more question about honoring the ancestors--even though ancestor worship in a domestic setting is like hero worship in manner, one does still kneel to the ancestors when at home, is that right?"

There is very little evidence that the ancient Hellenes prayed on their knees at all but if they did, it were almost always women and the situation was incredibly dire. Kneeling was percieved as a ritual act of last resort, pursued by those in victim positions, who fall down on their knees in desperation. Kneeling is above all a sign of hiketeia, submission, appropriate for girls and women, inappropriate in most cases for free men. It's not odd, then that kneeling was almost solely connected to the rites around mourning and death where women were charged with the loud wailing and obvious signs of anguish to honour the departed. This is evident in, for example, the Iliad:

"Meleager lay there, nursing his anger, embittered by his mother’s curse. For he had killed an uncle, her brother, and she had knelt and beat on the fertile earth with her fists, and drowned her breast with tears, and called on Hades and dread Persephone to destroy her son. And the Fury that walks in the darkness of Erebus heard her, she of the pitiless heart." [Bk IX:565]

There is a difference between kneeling in prayer and gestures connected to the Khthonic rites to the Gods. Or, perhaps more accurately, between the rites to the dead and the rites to the Khthonic deities. Those are very much not the same thing. The ancient Hellenes, when praying, stood upright with both hands raised above the head, palms facing upward and forward. Plato asserts that if you preferred to raise only one hand in prayer, you would raise the right to pray to the Olympians and the left to pray to the Khthonians. Kneeling was connected to the recently deceased, not the Khthonic Gods or the rites to the ancestors.

Now, I do not know exactly if you would raise your palms up or turn them down for rites to the ancestors. I'm nto even sure about sacrifice to the heroes. But I can make an educated guess. I assume that for both, the palms would be turned upwards. Many heroes were raised to the status of Gods and rites to the family line were performed to express pride in your blood and bring about good fortune as stemming from the family line. This is decidedly Ouranic in nature and thus the palms would be turned upwards.


"On the website of Labrys, which I'm certain you've heard of, I read that altars cannot be moved after dedication. However, as I have had a toddler in my house for three years now, I've been moving my statues, candles and other altar pieces to a safe location somewhere else simply for safety. Would you say that is alright?"

Yeah, I read that too. The short answer: that only held true for temple altars and I assume mostly for practical reasons: the altar was aligned to the temple, so unless the temple moved, there was no reason to move the altar and if you moved the altar, well, you had to move the entire temple. Not practical. What happened when worship was moved to a temple in another location was often that a new altar was built. It was just more practical.

Residential altars established for family worship or the altars at state buildings could be moved without issue. Remember, the altar is not a holy place in and of itself. A pile of stones or a heap of dirt could be an altar. Anything raised from the ground could serve as an altar. It's the rites performed on it that are sacred and that does not change if the altar is moved.