This saying and the next one are normally not included in Q because they are not a part of the double tradition (only found in gMatthew and gLuke in their Markan narrative context, so they are part of the triple tradition, not the double tradition). I believe however that they stood at the beginning of the sayings collection and were both deliberately ommited by both aMatthew and aLuke because these authors broke up the sayings collection and therefore they had no need for sayings that reflected on the sayings collection as a continuous (separate) text. They did however both copy the saying in its Markan context (Mark had chosen to use it in his gospel).
aMark chose to use only a limited number of Q-sayings in his narrative gospel. He builds his narrative around the sayings of Q (and aMatthew and aLuke then modify Mark's narrative and intersperse this with sayings from Q each in a different manner).
Note how aMatthew even mixes in yet another Q-saying within the Q-saying. aLuke tends to not move Q-sayings creatively around in the way that aMatthew does. aLuke keeps them together in blocks of sayings as he found them in Q.
Only the bold blue part is the relevant part from Q, the green/blue is the context in which it was placed by the Christian authors (blue is taken from Q).
Q
Q 8: 9-10 / Luke 8: 9-10 = Matthew 13: 11-12a, 13 (= Mark 4: 11b-12)
9 10 Unto you it has been given to know the secrets of the Rule of God; but to the rest through parables, so that looking they may not perceive; and hearing they may not understand.
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MARK
Mark 4: 2-20
2 And he taught them many things by parables, and said unto them in his doctrine, 3 Hearken; Behold, there went out a sower to sow: 4 And it came to pass, as he sowed, some fell by the way side, and the fowls of the air came and devoured it up. 5 And some fell on stony ground, where it had not much earth; and immediately it sprang up, because it had no depth of earth: 6 But when the sun was up, it was scorched; and because it had no root, it withered away. 7 And some fell among thorns, and the thorns grew up, and choked it, and it yielded no fruit. 8 And other fell on good ground, and did yield fruit that sprang up and increased; and brought forth, some thirty, and some sixty, and some an hundred. 9 And he said unto them, He that hath ears to hear, let him hear. 10 And when he was alone, they that were about him with the twelve asked of him the parable. And he said unto them,11 Unto you it is given to know the mystery of the Rule of God: but unto them that are without, all [these] things are done in parables: 12 That seeing they may see, and not perceive; and hearing they may hear, and not understand; lest at any time they should be converted, and [their] sins should be forgiven them. 13 And he said unto them, Know ye not this parable? and how then will ye know all parables? 14 The sower soweth the word. 15 And these are they by the way side, where the word is sown; but when they have heard, Satan cometh immediately, and taketh away the word that was sown in their hearts. 16 And these are they likewise which are sown on stony ground; who, when they have heard the word, immediately receive it with gladness; 17 And have no root in themselves, and so endure but for a time: afterward, when affliction or persecution ariseth for the word's sake, immediately they are offended. 18 And have no root in themselves, and so endure but for a time: afterward, when affliction or persecution ariseth for the word's sake, immediately they are offended. 19 And the cares of this world, and the deceitfulness of riches, and the lusts of other things entering in, choke the word, and it becometh unfruitful. 20 And these are they which are sown on good ground; such as hear the word, and receive [it], and bring forth fruit, some thirtyfold, some sixty, and some an hundred.
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MATTHEW
Matthew 13: 3-17
3 And he spake many things unto them in parables, saying, Behold, a sower went forth to sow; 4 And when he sowed, some [seeds] fell by the way side, and the fowls came and devoured them up: 5 Some fell upon stony places, where they had not much earth: and forthwith they sprung up, because they had no deepness of earth: 6 And when the sun was up, they were scorched; and because they had no root, they withered away. 7 And some fell among thorns; and the thorns sprung up, and choked them: 8 But other fell into good ground, and brought forth fruit, some an hundredfold, some sixtyfold, some thirtyfold. 9 Who hath ears to hear, let him hear. 10 And the disciples came, and said unto him, Why speakest thou unto them in parables? 11 He answered and said unto them, Because it is given unto you to know the mysteries of the Rule of Heaven, but to them it is not given. 12 For whosoever hath, to him shall be given, and he shall have more abundance: but whosoever hath not, from him shall be taken away even that he hath. 13 Therefore speak I to them in parables: because they seeing see not; and hearing they hear not, neither do they understand. 14 And in them is fulfilled the prophecy of Esaias, which saith, By hearing ye shall hear, and shall not understand; and seeing ye shall see, and shall not perceive: 15 For this people's heart is waxed gross, and [their] ears are dull of hearing, and their eyes they have closed; lest at any time they should see with [their] eyes, and hear with [their] ears, and should understand with [their] heart, and should be converted, and I should heal them. 16. But blessed [are] your eyes, for they see: and your ears, for they hear. 17 For verily I say unto you, That many prophets and righteous [men] have desired to see [those things] which ye see, and have not seen [them]; and to hear [those things] which ye hear, and have not heard (them).
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LUKE
Luke 8: 4-15
4 And when much people were gathered together, and were come to him out of every city, he spake by a parable: 5 A sower went out to sow his seed: and as he sowed, some fell by the way side; and it was trodden down, and the fowls of the air devoured it. 6 And some fell upon a rock; and as soon as it was sprung up, it withered away, because it lacked moisture. 7 And some fell among thorns; and the thorns sprang up with it, and choked it. 8 And other fell on good ground, and sprang up, and bare fruit an hundredfold. And when he had said these things, he cried, He that hath ears to hear, let him hear. 9 And his disciples asked him, saying, What might this parable be? 10 And he said, Unto you it is given to know the mysteries of the Rule of God: but to others in parables; that seeing they might not see, and hearing they might not understand. 11 Now the parable is this: The seed is the word of God. 12 Those by the way side are they that hear; then cometh the devil, and taketh away the word out of their hearts, lest they should believe and be saved. 13 They on the rock [are they], which, when they hear, receive the word with joy; and these have no root, which for a while believe, and in time of temptation fall away. 14 And that which fell among thorns are they, which, when they have heard, go forth, and are choked with cares and riches and pleasures of [this] life, and bring no fruit to perfection. 15 But that on the good ground are they, which in an honest and good heart, having heard the word, keep [it], and bring forth fruit with patience.