Deer FAQ

How high can a deer jump?

Higher than most fences, and the useful answer is a table rather than a number. Wild-caught white-tailed deer, tested against progressively taller fences, were deterred:

That is a jumping-ability test on wild-caught animals rather than a garden trial, so read it as the ceiling of what a deer can do, not a prediction of what yours will. Read the gaps rather than the rows. Nothing under five feet stopped a single animal, and the whole of the useful gain sits between six and eight — which is why six feet is the expensive mistake rather than a reasonable compromise. Going from five feet to six buys you fourteen points. Going from six to seven buys seventy-one. That is why a six-foot fence is the most common expensive mistake in this subject: it costs most of what a real fence costs and sits on the flat part of the curve.

One honest caveat. Those were motivated deer being tested on what they can clear in a containment setting, not deer deciding whether your garden is worth the effort. Treat it as the ceiling of ability rather than a prediction of behaviour.

There is also a way around the height entirely. Deer have poor depth perception and will not commit to a jump when they cannot judge the landing. Two parallel fences of four to five feet, set three to four feet apart, work about as reliably as a single eight-foot fence. That matters where an ordinance caps fence height. The same principle explains why small enclosures work: Minnesota Extension records micro-exclosures of 8 by 16 feet excluding deer at only 50 inches, which is the whole argument for fencing raised beds rather than the boundary.

Do deer go over a fence or under it?

Under, given the choice, because going under costs nothing. Deer crawl through gaps as small as six inches, which is why the ground line settles more fences than the height does.

Most failed garden fences are not failures of height. They are gaps at the ground line, a gate that does not seal, or a corner that sagged in the first winter.

When are deer most active?

Dawn and dusk, and increasingly at night where people are about.

GPS collars on 51 white-tailed deer across five Maryland parks, logging hourly for over a year, found they avoided residential areas during the day and moved into them nightly, especially in winter. If you never see the animals doing the damage, that is why.

Why did deer suddenly start eating a plant they ignored for years?

Three reasons, in order of likelihood.

The season changed. Late winter is the hungriest period, when fat reserves are lowest. Winter browse is poor enough that deer lose weight on it even where it is unlimited, which is exactly why a well-fed garden hedge becomes worth crossing a road for.

Pressure changed. More deer competing for the same forage means less selectivity. A plant passed over at low density gets browsed at high density.

The plant changed. New growth is softer and more attractive than mature foliage, so heavy pruning or a flush of nitrogen can turn an ignored shrub into a target.

There is a fourth thing worth knowing: it takes up to four weeks of feeding on a new food source for a deer to build the rumen microorganisms needed to digest it. An animal that has switched onto your hedge has invested in being able to eat it, and will not abandon that quickly because you started spraying.

Is any plant truly deer-proof?

No. Every reputable rating system describes relative preference rather than immunity, and the Rutgers list this site uses says so in its own introduction: no plant is deer proof, and results depend on local populations and weather.

Rarely Damaged means deer choose it last, not never.

Do deer eat plants that would poison other animals?

Yes, which is why toxicity is an unreliable defence. Yew is poisonous to horses, cattle and people, and Rutgers rates it in the worst of its four tiers because deer browse it heavily.

The toxic plants that do work, daffodils and hellebore among them, are avoided on taste and chemistry rather than because deer understand consequences.

What does it mean if deer are eating spruce or pine needles?

That the local population is under real pressure, rather than anything about your planting.

Spruce, fir and pine needles made up 58 to 60 per cent of the rumen contents of starved deer autopsied in late winter during past population peaks. In healthy deer they are a minor part of the winter diet. Deer eat them when there is nothing else.

Cedar is the exception. Arborvitae foliage is genuinely preferred over deciduous browse and every other conifer, which is why it is the most reliably destroyed hedge in the country.

Will a dog keep deer away?

A large dog outside regularly does help. A dog indoors most of the day does not, and the same habituation limit applies to every other deterrent.

The reason is the same one that limits every scent-based measure: deer habituate to a signal that never turns into a consequence. That is also why predator urine fades, and why rotating unrelated deterrents beats repeating one.

Can I plant a hedge instead of a fence?

Not as a substitute, and the reason is worth being precise about. The folk version -- deer will not cross a barrier they cannot see past -- is half right. Deer are genuinely reluctant to jump into ground they cannot assess, which is why a small enclosure works at 50 inches when a perimeter fence needs eight feet. But a hedge is not a barrier they cannot pass; it is one they can walk around, push through while it is young, and browse while it establishes.

Where a hedge earns its place is as structure in the planting: a solid mass of resistant shrubs makes a route unattractive and screens what is behind it. Treat it as one of the five design decisions, not as fencing you can grow.

Do motion sprinklers or ultrasonic devices work?

Motion-activated sprinklers do work, and better than most sprayed repellents, because the stimulus is sudden and physical rather than a smell that fades. They have the same limit as the dog: deer habituate. Move them, and accept that they are useless in freezing weather, which is when browse pressure peaks.

Ultrasonic devices have no support worth the name. No comparative trial has shown them reducing browsing, and the deer that walk past them are not doing so out of tolerance -- they are not being deterred at all. The full sequence of what actually works puts both in context.

Do deer avoid gardens near houses?

Less every year, and the Maryland collar study puts numbers on it. Female core ranges contained an average of 71 residential properties; male ranges 129. Deer bedded within 165 ftetres of homes.

Suburban deer are not visiting from somewhere else. They live there, with more forage and fewer predators than woodland offers. Proximity to your back door buys daytime human activity, which is real, and buys nothing at three in the morning.

How much does a deer eat in a year?

Roughly a ton of forage a year per deer. A mature forest produces only 50 to 100 pounds of browse per acre.

That arithmetic is the whole problem. A garden is a concentrated, irrigated, fertilised food source in a landscape that mostly is not.

The fence figures come from a containment study on white-tailed deer, and the collar work from suburban Maryland. Mule deer and black-tailed deer differ in browse preference, though not in the anatomy that produces torn rather than cut stems.