This handy tool allows you to figure out how many plants you need for any planting project. We designed it for sand dune restoration in New Zealand but it can be used by anyone who wants to do planting anywhere in the world. It is reportedly used for riparian planting too. Instructions are described in the guide below and the ‘print link’ is designed so you can just print your results and not this whole web page.
How the Planting Calculator works: The planting calculator uses pi radius squared (pi r2) to calculate the number of plants needed for any area. This is because plants usually grow in circles, not squares. So the calculation takes into account the space available between plants. Plants should not be planted in a grid when doing restoration plantings, but in groups.
This calculation concept was developed by Peter Handford, and Tim Park (Coastal Restoration Trust Trustee) brought it to the web.
Planting Calculator sponsored by Coastlands Plant Nursery.
Click here for up-to-date plant prices.
Coastlands Plant Nursery Ltd is NZs largest grower of coastal dune plants and pride ourselves on being the national dune revegetation centre. Specially built facilities allow us to propagate grow and supply coastal natives for large environmental projects, coastcare groups, councils and private landowners. We are passionate about the restoration and revegetation of our vulnerable coastlines and are proud to be involved in preserving New Zealand’s future.
Step One: Measure the area you want to plant and enter it into the “Area” box.
You can do this a number of ways. On a computer you can measure the width and length distances (area = average width times average length) using Google Earth or on sites like http://gis.doc.govt.nz/docgis/.
On the ground you can either use long (50m) tape measures, a measuring wheel, or by simply stepping it out (you can calibrate your normal step by walking a known distance (e.g. 100m rugby pitch) and counting your steps and dividing the number of steps (e.g. 143) by the known distance which gives you your normal step length (143/100=0.7m).
Step Two: Decide what species you want to plant and type their names into the “Species” boxes. If in doubt ask an expert.
The species you should plant will depend on the site i.e. proximity to sea and local conditions. Our calculator allows up to ten different species for each area. Spinifex and pingao are normally planted on the foredune and other species (e.g. sand coprosma, sand daphne, knobby clubrush, pohuehue) are planted in the mid and back dunes. Spinifex only occurs naturally in NZ’s North Island and the top of the South Island. See our website for more info. It is not essential to type the plant names in to complete calculations but it makes understanding the information much easier. Make sure you are getting eco-sourced plants –planting plants is a good thing, planting natives is better but eco-sourced are the best.
Step Three: Decide what proportion of each species you want and type them into each “Proportion” box next to the species you have entered.
The proportion of each species will depend on the site. The total percentage should equal 100%, or the numbers will not stack up, unless of course there are plants in the area that you want to keep (if this is the case, simply estimate or measure the area they occupy (e.g. 40%) and then only fill in the proportion you want to plant (e.g. 60%). A common mix is 50% spinifex and 50% pingao for most North Island dunes. Another mix could be 40% spinifex, 40% pingao, 10% sand coprosma and 10% sand daphne. Sand coprosma and sand daphne vary hugely throughout NZ so it is very important to eco-source them.
Step Four: Decide what spacing you want to use (in metres) and type it into each “Spacing” boxes next to the proportion boxes you have just entered.
Spacing will vary depending on the plant size at maturity, grade of plants (e.g. Root Trainer-Tinus (RTT), Root Trainer-Hilson (RTH), pots or planter bags (e.g. PB3)) and the local conditions. Please ensure you fill the box in using metres (e.g. 50cm = 0.5m). Spinifex and pingao are usually planted from root trainers (RTT or RTH) 0.6m apart, but closer together (0.5m) in very exposed or heavily used locations and further apart (0.8m) where they will grow fast and not be disturbed. Spacings of back dune species depend on the size of the plant at maturity and how fast you want canopy closure (e.g. the ngaio tree is normally planted about 5m apart from a PB3 but toetoe about 1.5m from a PB2).
Congratulations, you now know the “Numbers of plants to use”! To be practical you should round the numbers up to the nearest 5 or 10 when ordering
Step Five: Enter the cost of each plant into the box next to each species box.
Prices for each plant will vary from nursery to nursery, depending on the grade, and they usually change every year. Enter the cost per plant including GST (try to also include the delivery charge in the per plant cost if the nursery charges delivery per plant) or add it to the total if it is a fixed charge. Make sure you ask for eco-sourced plants from the local area.
Step Six: Estimate how many fertiliser tablets per plant you should use and enter them for each species.
Scientific trials have shown that survival rates of planted dune plants are significantly higher using slow release nitrogen fertiliser, this is possibly due to the large reductions in the seabird populations in the dunes (and their guano!). Most people find 10g tablets easier to use than granular fertiliser. We recommend a minimum of two (up to three) 10g tablets per dune plant. We recommend using a 20-4-4 (N-P-K) slow release fertiliser that is designed to last at least 12 months (preferably 24). Prices vary depending on suppliers, amount you purchase, and quality. Prices range from $0.10 (10c) to $0.20 (20c).