Do weeds between pavers grow up from underneath?

ICPI Tech Spec 6, the operation and maintenance guide for interlocking concrete pavement that CMHA now carries, corrects the idea directly: "Contrary to some views, weeds don't grow from the bedding sand, base, or subgrade. Weeds can germinate between pavers from windblown seeds lodged in the joints."

The picture it gives is a small one. A seed carried in on the wind settles into the sand at the top of a joint and germinates where it lodged. The layers Tech Spec 6 rules out as the source are the ones under the pavers: the bedding sand, the paver base and the subgrade. So a weed between pavers is, in Tech Spec 6's account, a seed that found a joint, not a root working up from below.

UF/IFAS Extension gives a Florida example. Writing about galinsoga, it says the weed is "commonly found in cracks in sidewalks and between patio pavers," that its seeds are easily transported by wind and water, and that in warmer regions of central and south Florida its germination may occur year-round. Galinsoga is UF/IFAS's example, not a name for whatever is growing in a particular driveway; identifying a weed is a question for UF/IFAS Extension. Green growth in a joint that is not a weed at all is a separate question, under why the sand in paver joints turns green.

Because the seed lodges in the joint, the joint is where the paver documents place a sealer's weed role, and each uses its own verb. Tech Spec 6: "Besides stabilizing the joint sand, sealers can prevent seeds from germinating, and prevent ants from entering." ICPI Tech Spec 5 says that "like stabilizers, sealers are also useful in stopping unwanted insects and weeds," and that like sealers, joint stabilization materials reduce the potential for weeds and insects in the joints. Can prevent, useful in, reduce the potential: none of the three is a statement that a sealed joint never grows a weed.

239 Exteriors describes its own sealing in its own words, as protection against "weed growth between joints." That is the company's description of its sealant, not an ICPI finding. Whether weeds come back after a sealing is a separate answer, on the service page's joint sand and weeds section.

Tech Spec 6's opening clause, besides stabilizing the joint sand, is a separate argument, made under what a sealer does for joint sand, and the stabilizer products themselves are defined under joint stabilization.

The sealer verbs are about seeds germinating. For a weed that is already growing, Tech Spec 6 gives a different instruction: "Weeds can be removed by hand or killed using steam or a herbicide. Take care in using herbicides so that adjacent vegetated areas are not damaged." Neither Tech Spec 5 nor Tech Spec 6 describes a sealer removing a weed that has already rooted, so in their sequence the weed comes out first, by one of those three routes.

Two other joint problems have their own answers. Sand dropping out of the same joints has its own causes, named under why the sand is washing out of paver joints. A paver that rocks or shifts underfoot is a question about the pavement, not about weeds, answered under whether sealing will fix loose pavers.

Sealers are not the only products sold with a weed line. Techniseal says of its polymeric sand, "Contrary to plain sand, it inhibits weed growth and deters ants." Tremron says polymeric sand can inhibit weed growth, ants and other things that may get lodged between the joints of pavers. SEK-Surebond's data sheet for its SB-1300 joint stabilizing sealer lists, among that product's benefits, that it stabilizes joint sand and reduces sand washout, weeds and insect infestation.

Each of those is a maker describing its own product, and each is about the joint itself, which is consistent with Tech Spec 6's account that the seed arrives from above and lodges there. Which jointing product or sealer suits a given surface is settled by the product's label and the paver maker, not by a general rule.