Helsinki Biochar Project

In the Siltamäki sports park five new sports turfs with a high-class growing medium were constructed during summer in 2023. The growing medium consists of 90vol-% sand and 10% peat. One field acts as an experimental site and in July 2023, a layer of biochar was mixed into the topmost 12-15cm layer of the soil. This required 22 m3 of biochar onto the 2925 m2 pitch and resulted in the top layer containing approximately 5% biochar. The turfgrass was established on site by sowing. 

A new kind of dynamic perennial planting was constructed in Kalasatama. The site is located in Työpajanpiha, in front of the house of the Helsinki Urban Environmental Division (KYMP). There are two plant community types that each received biochar in their soils. The plant communities are composed using principles inspired by a naturalistic planting design. The biochar was either enriched in advance with nutrients by mixing it with compost in 1:1 ratio, or applied with compost without pre-charging. The final volume of biochar in the substrate is either 0, 7 or 20%. The construction was completed in late 2023.

A new tram route was built in Kruunuvuori and in order to increase water infiltration, many stretches are now covered with hollow bricks called "riimukivi". The brick intervals are filled with sandy soil and sown with a grass mixture. As the depth of the soil is only 12 cm with gravel underneath, the growth environment is very dry. To improve the drought resilience and water availability, the soil was amended with 10% biochar. A comparison is made between three soils: one with 1:1 compost-charged biochar, one with biochar fertilized on site and one where a super absorbent polymer (SAP) is replacing biochar.

Located between the city library Oodi and the Musiikkitalo concert house, Tapahtumapuisto park and Makasiinipuisto park include vast lawns that are highly exposed and in intensive use.  In order to obtain better drought resilience and nutrient retention, a small percentage of biochar (~1 l/m2) was incorporated into the lawn soil. The original plan was to incorporate a minimum of 4l/ m2. The application was conducted together with an aeration procedure using the Turf Gamechanger machinery. The lawn was perforated, biochar was brushed into the holes and topped with fertiliser and a microbial inoculant.

The application rate of biochar was lower than intended and a remake was planned for the autumn. However this plan was rejected as the Urban Environment Division is mapping out the need for wider- scale renovations in the park area.

In September 2023, a different part of lawn was selected to serve as a test site for trying out a new method of lawn renovation with biochar. An area of 1500 m2 was first handled with a uniscratcher machine to remove most of the dead turf layer. Thereafter, 8 m3 of biochar was applied and rotavated into 15 cm depth. The soil was topped with turf soil mixture before resowing the grass seeds.

The Vaasanpuistikko square, located above the Sörnäinen metro station, is undergoing massive renovation. In the process, five oak trees planted in the 1980's remained in place. In order to improve their growth, three trees had their growing medium changed to structural soil instead of the old, compacted soil. The structural soil matrix was designed to carry the heavy load of the square, and hence it consists of a stony matrix. To improve the moisture and nutrient conditions, the space between stones is normally filled with soil. In this case the voids were filled with biochar, compost and soil. 

In line with the carbon neutrality targets, Helsinki is piloting sites where construction of infrastructure is aimed to be realized with net zero emissions. The second pilot is situated in Herttoniemi where the "itäbaana" bike street is being expanded. The park design includes planting 85 new tree individuals. Thirtyy six trees were selected to receive 10% of biochar in their growing medium. The biochar for this site was manufactured and donated by GRK, an infrastructure constructor company with its own ambitious climate targets. The biochar park  was finished in October 2023 and first measurements on tree dimensions were made to enable annual future follow- up of how biochar effects the tree growth.

Four individual parking spots around Helsinki were transformed into green islands. Coarse woodchip biochar which was pre-activated at HSY waste management facility with biocompost was used in the growing medium of a single existing linden tree. The old growing medium was partly replaced with structural soil and biochar was added to improve water- and nutriet retention in its root zone.  This tree is the first in Helsinki that had compost-charged biochar as the main component in the recipe. The initial plan was to realize the design according to the so-called Stockholm model including 75% stones and 25% of biochar-compost mixture, but the plan was adapted to 70% stones to comply with the conventions prevailing in Helsinki. Further, a soil component was added to the mixture of fine material, resulting in a recipe with 10 % commercial soil and 20 % of HSY woodchip biochar-compost mix.

In the Kalasatamasta Pasilaan (KaPa) project, long stretches of tram track are paved with similar hollow stones as in Kruunuvuori. On a specific area in Hermannin rantatie road, comparisons are made between 0, 5 and 10% addition of biochar and further comparing two different biochars. The biochars are pre-activated with compost, mixed at least 1 month in advance of construction. Whereas in Kruunuvuori the paving will grow grass and the growing medium is intended for park lawns, here it will have a mixture of flowering plants and a soil mixed from recycled sanding sand.

A new residential area will be built in Stansvikinkallio in the coming years. Many streets will have linden trees under paved surfaces and therefore the trees will get a structural soil around their roots. To find out what is the effect of biochar, as well as the effect of watering the trees with nutrient solution, an experimental setup has been planned. 

A part of the trees will be planted in a soil recipe that is an adaptation of the conventional Stockholm planting soil. It consists of 70% stones, 15% of biochar and 15% of compost. Some of the trees will receive nutrients along with the watering regime for the first two years of growing whereas in Stockholm the regime is continued for three years. To resolve the difference caused by this practice, some trees will only have pure water, which is the current practice in Helsinki.

Additionally, three trees will be planted without biochar which is replaced by conventional soil for broad-leaved trees.

The schedule of construction is open and will be timed as the general planning of the area proceeds.

A playground yard in "Leikkipuisto Vähätupa" in the Konala residential area is undergoing a renovation. An old gravel area was converted into a flowering meadow by adding on it a thin 10 cm layer of soil and seeds on top. There is relatively little knowledge about how biochar acts in meadow plant communties and wether its effect in the long run will be beneficial or not. Hypotheses range from beneficial increase in microbial activity and controlling of excess nutrients into unwanted functionality as a long-term fertilizer agent. To gain insight on the effects, half of the meadow received 10% of uncharged, raw HSY woodchip biochar into the 10 cm soil layer and half will remain without. The construction took place in late October.

The Jätkäsaari community garden is a mobile garden group consisting of around 15-20 gardeners. This gardening community makes use of the many derelict urban spaces in the local area waiting for development. Once development starts on the lot, the garden moves to a nearby available location. The concept arose from seeing opportunity for using derelict spaces in the neighborhood and because the initiators made use of a temporary lot at the Lapinlahden lähde garden from which they had to move. 

The infrastructure of the garden community is adapted to these temporal situations. For example, the gardeners only make use of 1m2 garden boxes placed on pallets so they can easily be moved. Gardeners can rent rights for a garden box for 7,- a year. This arrangement was negotiated with the City of Helsinki with the help of Dodo, a local urban environmental association.  

One mayor challenge for this community due to its need to be mobile is access to water: which is now tapped in the waste recycling room of a residential building located a couple hundred meters from the site. Another related challenge is water retention capability of the garden boxes: as they are positioned on top of pallets, the soils dry out easily. It is to be tested if biochar can play a role in reducing the irrigation needs of the Jätkäsaari community garden 

The Lapinlahti garden community is located in the Lapinlahti bay area in Western Helsinki and is part of the pro-Lapinlahti mental health association, who rent the land from the City of Helsinki. The garden consists of two parts: a larger part where gardeners rent individual plots of various sizes, and a part that is collectively maintained by a group of gardeners. 

The individual plot rental side of has a waiting list of interested farmers. Every year, if there are vacancies, new tenants are selected via a lottery system. Tenants of individual plots can also participate in voluntary group activities such as talkoots, a Whatsapp groups for discussions or collective purchasing of garden materials. Garden activities are coordinated by a small team. The communal side of the garden started as a means for people with mental challenges to provide wellbeing and relations to nature and teach gardening principles to beginners as a hobby. Participation in the communal garden is free of charge. 

Water retention of one of the larger issues in the Lapinlahti Garden Community, as it is not possible for most of them to visit the garden frequently enough to water the plants sufficiently. The gardeners were already aware of biochar as a potential solution for this challenge, but partly due to its high price it was never considered a viable option. In total 1250L of biochar was delivered to these garden communities, which was activated and applied during ‘talkoots’ (collective works) in the spring. 

Inner courtyards are located on the intersection of public and private space, and in Finland are often managed through a housing cooperation. Which offers a potentially interesting legal structure for citizen engagement. Especially related to the need of adapting houses to climate change.

Rinnekodit is a housing association that is conducting a pilot project in which it is creating a community setting providing support to help formerly homeless people to reintegrate into society. This pilot project takes place in a housing block in Eastern Helsinki. Gardening in the inner courtyard is part of the reintegration program. Small adjustments to the inner courtyard have been made to facilitate communal activities and enable community gardening. The coordinators working for Rinnekodit did not have much experience with gardening prior to the project and are learning through trial and error. 

Using biochar was part of a larger event to kick-off Rinnekodit’s project to convert the inner courtyard into a therapeutic garden. Adding biochar to 6 pre-existing garden boxes, installing a new garden box with annual flowers, amending soil around already present berry bushes, adding biochar to a planting area next to a sidewalk, and donating and constructing a planter box filled with compost and biochar to a neighboring elderly home.

Rooftops provide are an underutilized space for potential urban green. Because biochar is light in weight and has a large nutrient and water holding potential, it can be an interesting instrument in creating special soils for rooftops.

On top of the roof of Kaapelitehdas, an arts and culture centre in Western Helsinki, a group of 40 raised garden boxes belong to a community of gardeners who also rent studios in the building. 

250L of dry biochar was delivered to the rooftop garden of the Kaapelitehdas. In advance a leaflet with information on how to activate and apply biochar was distributed to one of the coordinators of the rooftop garden, who forwarded it to the gardening community. The gardeners were free to decide how they wished to apply the biochar and for what purposes. In addition, one of the garden boxes was reserved to do a comparative test with a selection of native plants that attract pollinators. 10L of activated biochar (with nettle tea) was mixed in one half of the soil, while the other half did not receive any biochar.