Well, not quite thin air, because plants, like the rest of us, require nutrients and water to grow. Although the word “aeroponics” does not show up in either of the dictionaries I use for handy reference, and is totally ignored by my spellchecker, it is actually common enough that it should be appearing in any current dictionary of the English language. I admit that I had no idea what the word meant when Yehudah asked me the following shaylah:
“To overcome the many problems that may be involved in purchasing products during shemittah, we want to purchase a large aeroponics kit and grow our own vegetables. Will this present us with any halachic problems in terms of either the laws of shemittah, or the laws of kelayim?”
And so, I began my education about this subject. This is what I discovered:
Aeroponics is a method of growing vegetables or herbs without soil by spraying the plant roots with water and nutrients (as opposed to hydroponics where the roots are submerged in a nutrient solution). Although it can be done on a commercial scale, the company Yehudah contacted sells aeroponic kits for growing herbs and vegetables in the comfort of one’s home. Each kit includes the seeds and nutrients required for specific types of plants, a complete, self-contained, open-top growing tank that includes its own light fixtures and instructions on how to make it all work. Just add water and electricity to run the pump and lights.
The company advises growing lettuce, herbs, tomatoes, peppers, or strawberries each in its own tank, since they have quite different needs. Nevertheless, the first question we will discuss is whether this is a halachic requirement to do so because of the prohibition of kelayim.
WHAT IS KELAYIM?
It is important to clarify a common misconception. The prohibition of kelayim is not the creation of a new species; it is the appearance that one is mingling two species together. This is why hauling loads with two species of animal, grafting one tree species onto another, mixing wool and linen in a garment or planting grains in a vineyard are all Torah violations of kelayim, although none of these acts affect the genetic make-up of the species.
Yehudah’s question involves two halachic topics:
Could someone gardening on his desktop possibly violate the mitzvah of kilei zera’im, which prohibits planting two species together or near one another? Violating this prohibition requires three basic conditions, all of which Yehudah met:
- The prohibition applies to herbaceous, as opposed to woody plants, meaning that it does not apply to trees and shrubs, but it does apply to vegetables and many herbs. Thus, one may plant seeds of different trees together, yet one is forbidden to plant a mix of vegetable seeds (Rambam, Hilchos Kelayim 1:6).
- The prohibition of kilei zera’im applies only to edible crops (Rambam, Hilchos Kelayim 1:4). Thus, one may plant seeds of different ornamental flowers and grasses within close proximity.
- It applies only in Eretz Yisroel (Kiddushin 39a), and is min hatorah according to most halachic authorities, even today (implied by Rambam, Hilchos Kelayim 1:1). (However, note that in Rashi’s opinion [Shabbos 84b, s. v. ve’achas] the prohibition of kilei zera’im in Eretz Yisroel is only miderabbanan and Tosafos [Yevamos 81a, s.v. mai] contends that although kilei zera’im is essentially min hatorah, in our era it is only rabbinic because most of the Jewish people do not currently live in Eretz Yisroel.) Therefore, someone in Chutz La’Aretz may plant his backyard garden with a wide variety of herbs and vegetables, without any concern for how close they are, whereas in Eretz Yisroel, someone planting a garden patch must be very careful to keep the different species separate (Rambam, Hilchos Kelayim 1:3). I will discuss later how far apart one must plant different species to avoid violating this prohibition (see Chazon Ish, Hilchos Kelayim 6:1).
One may not plant in Eretz Yisroel during shemittah. Does planting this indoor garden in Eretz Yisroel violate the laws of shemittah?
Yehuda’s question requires analyzing the following subjects:
Do these mitzvos apply when planting indoors?
Would they apply when planting outdoors in a pot or planter that is disconnected from the ground?
Do they apply when one is not planting in soil?
Two Talmudic passages discuss whether agricultural mitzvos apply indoors. In Eruvin (93a), the Gemara prohibits planting grain in a vineyard that is underneath a roof extending from a house. This passage implies that agricultural mitzvos apply within physical structures.
On the other hand, the Talmud Yerushalmi (Orlah 1:2) discusses whether three agricultural mitzvos, orlah (the prohibition to use fruit produced in the first three years of a tree’s life), maaser (tithing produce), and shemittah, apply to indoor plants. The Yerushalmi rules that whereas orlah applies, there is no requirement to separate maaser on produce grown indoors. The Yerushalmi questions whether shemittah applies to indoor produce, but does not conclude clearly whether it does or not.
WHY IS ORLAH DIFFERENT FROM MAASER?
The Yerushalmi notes that when the Torah instructs us to separate maaser, it states: You shall tithe all the produce of your planting, that which your field produces each year (Devarim 14:22). Since the Torah requires maaser only on produce of a field, there is no requirement to separate maaser from what grows indoors, since, by definition, a field is outdoors. Therefore, one need not separate maaser min hatorah when planting indoors, even if one is planting directly in the soil floor of the structure. (The Rishonim dispute whether there is a rabbinic requirement to separate terumos and maasros when planting in the ground within a building; see Rambam and Raavad, Hilchos Maasros 1:10.)
However, when the Torah describes the mitzvah of orlah, it introduces the subject by stating When you will enter the Land (Vayikra 19:23). A tree planted indoors is definitely in the Land of Israel, and thus is included within the parameters of this mitzvah, even if it is not in a field.
Do the laws of shemittah apply to produce grown indoors? Does shemittah apply only to a field, or to anything planted in the Land of Israel?
The Yerushalmi notes that when the Torah discusses the mitzvah of shemittah, it uses both terms, land (Vayikra 25:2) and field (Vayikra 25:4). It is unclear how the Yerushalmi concludes and the poskim dispute whether the mitzvah of shemittah applies indoors in Eretz Yisroel. Ridbaz (Hilchos Shevi’is, end of Chapter 1), Chazon Ish (Shevi’is 22), and Pnei Moshe all rule that it does; Pe’as Hashulchan (20:52) rules that it does not. Most later authorities conclude that one should not plant indoors during shemittah, at least not in the soil. I will discuss, shortly, whether one may plant during shemittah indoors hydroponically or in an indoor area where the dirt floor is covered.
May one plant different species next to one another indoors? Does the prohibition of kelayim apply to produce planted under a roof?
Based on the Talmud Yerushalmi we quoted above, we should be able to establish the following rule:
When the Torah commands that a specific mitzvah applies to the land, it is immaterial whether the planting is indoors or outdoors. However, when the Torah commands that a mitzvah applies to a field, it does not apply indoors. As noted above, an indoor area can never be called a field.
How does the Torah describe the mitzvah of kilei zera’im? The Torah states “you shall not plant kelayim in your field” (Vayikra 19:19), implying that the mitzvah does not apply indoors. Thus, we should conclude that there should be no prohibition min hatorah against planting herbs or vegetables proximately if they are indoors. (Nevertheless, both the Yeshuos Malko [Hilchos Kelayim 1:1] and the Chazon Ish rule that kilei zera’im does apply indoors and apparently disagree with the above analysis. I will take this into consideration later.) However, it is probably prohibited miderabbanan, according to the opinion that the Sages required tithing produce grown indoors.
At this point, the discerning reader will note a seeming discrepancy with the passage from Eruvin 93a that I cited earlier. The Gemara rules that one may not plant grain in a roofed vineyard, implying that kelayim does apply indoors. This seemingly conflicts with my conclusion based on the Yerushalmi that one may plant different herbs or vegetables proximately indoors, without violating the prohibition of kelayim.
THE SOLUTION: GRAPES VERSUS VEGETABLES
The answer is that there is a major halachic difference between the two cases: Planting grain in a roofed vineyard violates kilei hakerem, planting other crops in a vineyard. Although both kilei hakerem and kilei zera’im are called kelayim, kilei hakerem is a separate mitzvah and is derived from a different pasuk than the one prohibiting kilei zera’im, planting herbaceous species together. The Torah commands us about kilei hakerem by stating: “You shall not plant your vineyard with kelayim (Devorim 22:9), using the word vineyard, not field. Whereas a field cannot be indoors, a vineyard could.
At this point, we have resolved the first of our questions asked above:
“Do these mitzvos apply when planting in a covered area?”
The answer is that planting kelayim species should seemingly not apply, although some prominent authorities disagree. Shemittah does apply, according to most poskim.
We now progress to our next question:
Do agricultural mitzvos apply to plants growing in Eretz Yisroel in closed pots and planters that are separated from the ground and yet exposed to the elements?
The Mishnah (Shabbos 95a) teaches that someone who plants in a flowerpot that has a hole in its bottom, called an atzitz nakuv, violates Shabbos as if he planted in the earth itself. However, planting in a flowerpot that is fully closed underneath, called an atzitz she’aino nakuv, is forbidden only because of rabbinic injunction and does not involve a Torah-prohibited violation of Shabbos. The same categories usually apply to agricultural mitzvos: plants in a pot with a hole in the bottom are equivalent to being in the ground itself; those whose bottom is completely sealed are included in agricultural mitzvos by rabbinic injunction.
Therefore, one must separate terumah and maaser from produce grown in pots or planters, whether or not the containers are completely closed underneath, and one would violate kelayim if one planted two species near one another in a flowerpot or other container.
There are some exceptions to this rule. In some instances, planting in a closed container is the same as planting in the ground. According to the Rambam [Hilchos Maaser Sheni 10:8] and the Shulchan Aruch [Yoreh Deah 294:26], orlah applies min hatorah to a tree planted in a closed flowerpot. The reason for this phenomenon is that a tree root will, with time, perforate the bottom of its pot, and therefore, it is already considered to have a hole and be part of the ground below.
SHEMITTAH IN A HOTHOUSE
On the other hand, there are also poskim who contend that shemittah does not apply at all, even miderabbanan, to items planted in a planter or flowerpot whose bottom is completely closed. What is the halacha if one plants in a covered area in a pot that is completely closed underneath? May one be lenient, since the pot is both indoors and is also an atzitz she’aino nakuv, which is not considered connected to the earth min hatorah? This question leads us directly to the following question that Israeli farmers asked, about sixty years ago: May one plant in a hothouse during shemittah, in a closed-bottom vessel? As I mentioned above, although some authorities permit planting in the soil indoors during shemittah, the consensus is to be more stringent. However, many poskim permit planting in pots in a hothouse, if its floor is covered with a thick material, such as heavy plastic or metal (see Chazon Ish, Shevi’is 26:4; Mishpatei Aretz pg. 239; however, cf. Shu’t Shevet HaLevi who prohibits this).
AEROPONICS AND SHEMITTAH
At this point, we can discuss our original question: Aeroponics, like a hothouse, means growing indoors, and is also similar to planting atop a floor that is covered with metal or heavy plastic. Based on the above discussion, we may conclude that most authorities would permit planting aeroponically during shemittah, provided that the bottoms of the tanks are metal or plastic.
WHAT ABOUT KIL’EI ZERAIM?
We still need to explore whether desktop planting violates the laws of kilei zera’im.
I concluded above that there is probably only a rabbinic prohibition of kilei zera’im on indoor planting, but that some prominent authorities prohibit it min hatorah. Can we offer a solution for Yehudah’s plans? To answer this we need to address another issue.
KEEP YOUR DISTANCE
As I mentioned in the beginning of this article, kelayim occurs when different species are mingled together. If there is enough distance between the plants, no mingling is transpiring.
How far apart must I plant herbs or vegetables to avoid violating kelayim? This is a complicated topic, and its answer is contingent on such factors as how and what one is planting. I will, however, go directly to the conclusion that affects our case.
Since the desktop garden involves only herbs and vegetables and only a single plant or a few plants of each species, the halacha requires only a relatively small distance between species. Min hatorah one is required to plant only one tefach apart; the additional space requirement is rabbinic (see Rambam, Hilchos Kelayim 3:10). The poskim dispute how distant one is required to avoid a rabbinic prohibition. Some require that the plants are at least three tefachim apart [about ten inches] (Rashi, Shabbos 85a), whereas others determine that it is sufficient for the plants to be only 1½ tefachim apart [about five inches] (Rambam, Hil. Kelayim 4:9; Shulchan Aruch, Yoreh Deah 297:5). In the case of the aeroponically-grown produce, since the tanks are completely closed underneath, they have, at worst, the halachic status of atzitz she’eino nakuv, a closed pot or planter, considered part of the ground only because of rabbinic injunction, but not min hatorah. We can, therefore, conclude that as long as the seeds are placed more than a tefach apart, we avoid any Torah prohibition. As far as the possible rabbinic prohibition if the plants are only a bit more than one tefach apart, we could additionally rely on the likelihood that kilei zera’im does not apply indoors in an eino nakuv planter.
Having completed the halachic research, we corresponded with the company that produces the desktop planting kits, asking them how far apart are the holes in which one “plants” the seeds, and how many different herbs and vegetables can be planted in a single tank.
The company replied that the kit usually has seven holes, each four inches apart from the other, center to center. When planting peppers and tomatoes, which grow larger than the greens or herbs, the company recommends plugging four of the holes and using only three, which are far enough apart to avoid any kelayim issue, according to our conclusion. However, when planting herbs and greens, the distance between the holes is just about the distance that might present a halachic problem. I therefore advised Yehudah to plant in alternative holes, even when planting herbs of different varieties.