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I was wondering what the distance is when planting Japanese box hedge. I plan to space them every 20cm as the height of the hedge will be approx 30cm when trimmed.

Is 20cm the correct spacing?

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Rather depends what you mean by Japanese box hedge - as far as I'm concerned, it means varieties of Buxus microphylla (as opposed to Buxus sempervirens). Although the varieties differ a little in height and spread, the general rule for planting as a hedge is aroiund 10 cm apart. The link below is to the RHS,where they talk about a much closer planting distance, but the consensus generally appears to be between 8-12 cm - the variation in planting distance is likely down to particular varieties. As your hedge is going to be a low growing one, you need not worry too much about creating a pronounced wedge shape (wider at the base than the top) as it grows - these little dividing hedges are often used as edging around planted areas, and are usually relatively straight from top to bottom.

https://www.rhs.org.uk/advice/profile?PID=88

  • Japanese box is usually Ilex crenata and varieties, Bamboo. One can use these guys for knotgarden tiny little hedges, especially the boxwood for tiny little hedges. ALL hedges need to be narrower on the top width and larger on the bottom width. This is a big deal in all pruning. If the leaves on the bottom aren't given more light the plant will stop feeding the bottom of the hedge and one will most certainly get thinning! Pruning natural shrubs the shrub should have a ratio of 1:2 or 1 : 1 1/2 or 2 feet high by 4 feet in width at the bottom, like a salad bowl turned upside down. – stormy Sep 28 '16 at 21:21
  • I see all these hedges that are straight up and down (or worse narrower at the bottom than the top) and shake my head or worse. The bottom of a hedge HAS to be wider than the top because the leaves at the bottom need to get at more sunlight to stay up with the production of food the leaves provide the plant at the top of the hedge. It is relative per plant. Straight up and down will put the leaves at the bottom at a serious disadvantage. If leaves are not able to produce food for the plant as much as the top leaves those leaves will be shunted from food and water. Producers get fed. – stormy Sep 28 '16 at 21:26
  • Not only hedges but when pruning trees, native grasses, au naturale shrubs, the rule is the base is ALWAYS wider than the top. I am kinda a master pruner. Straight up and down is a big no no! Grins. It would be nice to know exactly where this OP's hedge will be and what it's function will ultimately be. Waist height or close is far better than teensy tiny hedges that need lots of vigilance, pruning and stocking up on substitutes (for eventual death of vital members in a hedge) for novice gardeners. I need to figure out how to easily send graphics for explanations...later!! – stormy Sep 28 '16 at 21:35
  • @stormy when I googled japanese box, it came up with Buxus; and I said 'relatively' straight, not 'straight' - 30 cm is pretty short, so if he's using it as a 'jewel' box, it shouldn't really be so wide its practically cone shaped - but one, we don't yet know which plant he means and two, what purpose the low hedge will serve – Bamboo Sep 28 '16 at 21:35
  • Your search came up with Buxus? Sempervirens is just a 'looser' softer form of boxwood. I googled Buxus and came up with...get ready...AMERICAN boxwood ! How funny...I have known it as Common Boxwood. Japanese is definitely Ilex...crenata. And your image of cones isn't right... I am talking about 2 -3 inches the base wider than the top. Looks normal, not a wedge. Plants with bigger bottoms also appear more solid, because they are. Grins. – stormy Sep 28 '16 at 21:41
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Ilex crenata? Any other varietal name attached? If I do my metric calculations this is 6 inches by 12 inches high? Way too small for height. I would make the height at least 2 1/2 feet by 2 1/2 feet wide. You are probably looking at 1 gallon baby plants. Plant 1 1/2 feet apart and at least 1 1/2 feet from the edge of the walk.

Dig up the soil and turn over to make a slightly raised bed using a rake and compacting the top of the soil firmly with a chunk of plywood and jumping up and down on it. Have you tested your soil? Make sure the hedge 'goes around corners' to stabilize the hedge in your landscape. You don't want a fast hedge of immature plants. Your sizes might work for a knot garden but not near structures meant for humans. And then the size is iffy for the health of the plant. It is normally much larger, planted in the garden it can't be treated like a Bonsai.

Make a template for hedging. The bottom of the hedge HAS TO BE WIDER than the top by at least 1 1/2" per side. Your hedge is 2' 1/2" high (relax, it will look great for the two years to become a hedge), the bottom of the hedge should be minimum 2' wide, ...so the bottom is 2' or 24 inches; the top width is smaller, 24 minus 3" at 21" (this is critical so that the bottom of your hedge gets as much sun in relation to the top, promoting a thick hedge to the ground).

When hedging imagine yourself in a stiff vice making as little movement as possible. Like a robot. String lines for guides. Sharpen your hedger or your hand shears! Keep your cutting edges on the plane of the sheared sides or top.

Ilex is a super choice for hedges. There are also pillar shaped Ilex that look spectacular, accentuate the verticals in your architecture that will tie your hedge into the landscape and your home.

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