Do I need a pond net in fall, and what size?

If trees drop leaves anywhere upwind of your pond, a fall net saves you a spring cleanout. Size it from the pond's longest and widest spans, measured to the outside of the rock edge, plus two feet on every side, and raise the middle so leaves roll off. Put it on before the leaves turn and take it off once they are down, before the first heavy snow.

What the manufacturers and extension sources say

The reason to keep leaves out is what they do once they sink. University of Illinois Extension's Emily Swihart writes that leaves decomposing in water release nutrients, and that "One of the primary nutrients made available during decomposition is phosphorous." The RHS says a few leaves do no harm, but heavy leaf fall calls for netting because accumulated debris "can encourage growth of algae and weeds."

On size, the clearest rule comes from a net maker. Kevin Wintringer, president of KW Solutions, writes in POND Trade Magazine: "We recommend adding two feet past all rocks and the water's edge." In a second article he adds that "When a pond gets larger than 15 feet in any direction, additional support is recommended," and names pillows, PVC pipe, or "solid nylon wire and inline tensioners." Other sellers give smaller margins, and mesh advice varies by product.

The Pond Guy explains the mesh choice by leaf type: for pine needles and small leaves "you'll need a small mesh net," and for big, heavy leaves a stronger net that can carry the weight. On shape, it says "A tented design will make sure leaves and debris fall off instead of building up."

On timing, The Pond Guy says to "Remove your pond nets when the last of the leaves have fallen, but before the first major winter storm," and that "Pond netting should not be used in winter," because a net loaded with debris "could become weighted down and collapse into the pond." Wintringer says to put the net on "before the first signs of colorful foliage." Aquascape's fall-care page refused our fetch; its search snippet says to net while the leaves are still on the trees, and to check the skimmer every couple of days early in the season and daily once fall is in full swing. The Aquascape Signature Series 200 skimmer manual warns that "Too much debris can reduce the water flow to the pump."

What contractors and pond owners do

Colorado Pond Pros tells customers with an irregular pond to "measure the longest and widest parts," and to take the net off before snow. Atlantis Water Gardens advises building "a 'tent' effect by using PVC hoops or a center pole" so leaves roll off instead of piling up in the middle.

Owners on Garden Pond Forum build that tent from whatever is at hand. In one thread, bagsmom describes a frame of "6 foot tomato stakes" with "thin bamboo for the horizontal braces," angled so leaves slide onto a stone beach where they are easy to pick up. In the same thread, mgmine staked a net flat to the ground and reports that it "sinks into the water in a day or two." In another thread, mrsclem is building "Frames from pvc and electrical conduit" over two ponds.

Whether a skimmer can replace the net is where owners disagree. In a thread titled "I'm planning to never net my pond," combatwombat planned to rely on a negative-edge skimmer with the pumps running all winter. Moderator Lisak1 answered that people net "because they get so many leaves that the skimmer makes very little difference," and said her pond still fills with wind-blown leaves although no trees near it drop any. A poster named poconojoe skipped the net one fall and found in spring that the debris on the bottom was "decomposing already." BKHpondcritters does not net, runs the pumps and skimmer all year, and scoops leaves by hand on a regular basis. On mesh, addy1 prefers a wide weave because "nothing gets stuck and it stops the heron," while Tula uses fine mesh and regrets that it keeps birds away from the waterfall.

Where the sources differ

The overhang figures range from about 10 inches a side (Thrive's 50 cm total) to two feet past the rocks (KW Solutions). Only the two-foot figure comes from a net maker, and only it says to measure from the outside of the rocks. A net measured to the water's edge on a pond with a one-foot rock border is two feet short before any overhang.

The net math borrows from the liner formula with one change. A liner adds twice the depth because it runs down one wall and up the other, and a net never goes down, so depth drops out. A raised net needs a little extra instead, and no net maker publishes how much. If the peak sits two feet up and the net reaches the ground nine feet away on each side, each side takes the square root of 9 squared plus 2 squared, or about 9.22 feet of net. That is our arithmetic, not a published rule.

Timing also splits by climate. Thrive, writing for the UK, says "The net can stay on through winter." The Pond Guy says to remove it before the first major storm, because a loaded net can collapse into the pond. Where snow sits on the ground for weeks, follow The Pond Guy. For what to do with the pond once the net is off, see winterizing a koi pond.

How to size and fit a net

Measure the longest span across the pond and the widest span at right angles to it, to the outside of the rocks, including any stream you want covered. Add two feet at each end of both spans. If the pond is over 15 feet in either direction, plan a support: a ridge pole, PVC hoops or tensioned nylon wire. Then allow for the rise of the tent on the sides it slopes toward.

That pond needs a net of at least 27.2 by 18.4 feet. Of Aquascape's three stock sizes, only the 28 by 30 foot net covers it in one piece. With the two-foot rule and a flat net, each stock size covers a pond up to the size below, measured to the outside of the rocks.

A pond of around 1,000 gallons may fit under the 14 by 20 foot net; check its spans against the table. The Pond Guy's framed kit adjusts to cover "anywhere between 4' x 6' to 16' x 11'." For a 20,000 gallon pond more than 24 feet across, you will either overlap two nets over wire runs or rely on the alternatives below.

Fit the net before the trees turn. Choose fine mesh under pines or small-leaved trees, as The Pond Guy advises, and a stronger net where the leaves are big and heavy. Leave the skimmer lid reachable. Clear the net with a leaf blower or brush whenever leaves collect, because a sagging net drops wet leaves straight into the water. Take it off when the last leaves are down and before snow.

When a skimmer or vacuum is enough

A skimmer can handle light leaf fall on a pond with few trees nearby, as long as the pump runs and someone empties the basket daily at the peak. Under mature trees, the forum owners above found it was not enough. For ponds too big to net, The Pond Guy suggests aeration, beneficial bacteria and manual removal, including a five-foot-wide surface skimmer and a three-foot-wide rake. For leaves that have already sunk, use a pond vacuum; a retailer listing for the OASE PondoVac Classic gives it 1400 watts, a 7 gallon tank and suction "up to 6 feet" deep. A vacuum cleans up the bottom but does nothing to stop more leaves falling in.

Getting the spans from your outline

If you have traced your pond in the PondTools app, the trace already holds the longest and widest spans. Open the PondTools liner calculator (also standalone) and it fills in both spans from your outline. It takes longest span, widest span, maximum depth and overhang in inches, plus a fold allowance. To size a net, set the depth to 0, set the fold allowance to none, and enter 24 inches of overhang plus the width of your rock border if your trace follows the water's edge. For the worked example above that is 240 by 144 inches with 36 inches of overhang, which gives 26 by 18 feet before the tent slope. The PondTools surface area calculator (also standalone) takes the surface area in square feet, typical water temperature, the coldest night you plan for and the kind of fish, and sizes the de-icer you will need once the net comes off.

Sources

• From trees to trouble: how leaves harm water quality, University of Illinois Extension
• September ponds, Royal Horticultural Society
• The Many Benefits of Pond Leaf Netting, Kevin Wintringer, POND Trade Magazine
• Maintaining Your Backyard Beauty, Pond Netting 101, Kevin Wintringer, POND Trade Magazine
• Pond Nets & Netting, Webb's Water Gardens
• Netting a pond, Thrive
• Aquascape 14 x 20 Protective Pond Netting listing, 123Ponds
• Protective Pond Netting, Aquascape (sizes via search snippet; page refused fetch)
• 6 Easy Steps for Fall Pond Care, Aquascape (search snippet; page refused fetch)
• Aquascape Signature Series 200 Pond Skimmer instruction manual, Splash Supply Company
• Choose Pond Netting, The Pond Guy
• I need a net to protect my pond from leaves, The Pond Guy
• How do I keep leaves out of my pond if it is too large for a net cover, The Pond Guy
• OASE PondoVac Classic listing, Pondscape
• Pond Netting for Falling Leaves, Colorado Pond Pros
• Koi pond netting how-to, Atlantis Water Gardens
• I'm planning to never net my pond, Garden Pond Forum
• Best way to keep leaves out of the pond, Garden Pond Forum
• Pond netting construction, Garden Pond Forum