Hydrangeas – Gardener Report

Whether you can grow hydrangeas under pine trees depends on the density of the trees canopy. If the canopy is too thick it will deprive the hydrangea of sun and rainfall. If the canopy allows some dappled light then you will be able to grow hydrangeas if you water them diligently and amend the soil. If you have a pine tree that allows partial shade or dappled light to reach the area where you want to grow hydrangeas then there are a few other conditions that you must get right first to ensure that your hydrangeas not only live but thrive and produce beautiful blooms… Soil and watering Under Pine Trees The first and most important problem when planting a hydrangea is finding a clear area of soil as pine tree have an extensive and shallow root system. If the tree is an old established pine then you can remove some roots with an axe without causing any lasting harm to the tree. I personally have had to remove sections of root many times as a landscape gardener and the trees are never phased. Once you have found space the next factor is… Soil pH- The soil pH under pine trees will naturally be acidic as this is the soil that pine trees themselves prefer and the soil is likely composed of many generations of mulched down, decomposed pine needles which are also slightly acidic or pH neutral. It should be noted that whilst pine needles are particularly acidic when the fall from the tree, once they have decomposed the resulting organic matter is either slightly acidic or pH neutral so pine needles will have less of an influence over soil pH then most people believe. Fortunately hydrangeas do very well in acidic soil and notably there flowers will be blue if the are of the species Hydrangea macrophylla (Bigleaf hydrangeas). You can manipulate the colour of hydrangea flowers to turn pink by increasing the pH of the soil by adding lime or wood ash (which are both alkaline) although this is quite tricky to get right! Soil structure- The soil structure underneath pine tree will not be ideal for growing hydrangeas however with a few amendments you can adjust the conditions so that they are better suited. What you will need to do is add lots of organic matter to the area of planting to a depth of over 6 inches and to a width that will accommodate the size of the root system of your hydrangea at full maturity. Farm manure, leaf mould, or just general garden compost are all good options as they will retain moisture incredibly well and allow for good drainage so water doesn’t collect or pool around the roots. They will also add fertility and maintain a soil pH of around 6-7. It is essential that you add this organic material as the main reason hydrangeas die is because they are not able to take up enough water from the soil. Organic material such as compost will help maintain the correct moisture balance in the soil that hydrangeas love. Mulching helps Retain Water Under Dry Pine Trees Hydrangeas that are under pine trees with restricted access to moisture will benefit from regular mulching. Apply a layer of mulch 2 inches thick on the surround soil of your hydrangea. Keep a distance of 6 inches between the mulch and the woody stems of the hydrangea as they do not like to be exposed to consistently moist material. Mulch will improve the soil texture and retain water so that the soils underneath remains at the right moisture balance for the roots of the plant. There are also the added benefits of: Adding nutrients to the soilStimulating the soils beneficial ecosystemSuppressing weed growth Adding mulch to the area around hydrangeas is most important straight after planting as this is the time when the plant is most vulnerable to drought. You can use many different materials for mulching but the best for dry conditions will be compost, manure and leaf mould as they have the best capacity for holding moisture yet they structure allows for good drainage which is perfect for hydrangeas. Watering Hydrangeas Under Pine Trees One of the biggest challenges for plants under pine trees is making sure that they are receiving enough water. Pine trees can restrict the availability of water from rainfall by: Intercepting the rain in the canopy so that it doesn’t reach the soil belowPine tress can soak up all the moisture in the soil with there extensive and thirsty root system and limit the available moisture for your hydrangea. This means that regular watering of hydrangeas is essential in the spring and summer months as hydrangeas are thirsty plants. The saving grace of being under a pine tree is that there will be a good amount of shade which will stop the soil drying out so quickly. The best way to maintain the optimal soil moisture for hydrangeas is to use soaker hose irrigation system which can gradually release water slowly during the hottest days of summer. If that’s not possible then I would recommend watering your hydrangea with around 2 gallons of water once every two or three days during the growing season. The soil needs to be moist so if the surrounding soil is dry to a fingers depth then you will need to increase the frequency of your watering. In the hottest days of summer I would recommend water every other day. This may seem like a lot of water but you have to bare in mind the hydrangea will be competing with the roots of the pine for moisture so it’s important to monitor the moisture of your soil and adjust for the changing weather. During the Winter months your hydrangea should not need any additional moisture as it enters its state of Winter dormancy. Is There Enough Light for Hydrangeas? Hydrangeas will have a tough time growing in full shade and even if they are able to establish they will not live up to their potential and produce lots of flowers. If your pine tree is casting complete shade over your hydrangea planting site then I would consider the possibility of tactically removing braches to let the light in. Established pines will have no difficulty tolerating some pollarding (branch cutting) at any time of year, but winter is the best time to do this. Hydrangeas of all species thrive in morning sun with shade in the afternoon. They can grow in full sun but shade slows the rate of soil so some shade is preferred. If your pine tree cast consistent dappled light on the ground below then this will be enough to grow hydrangeas as long as the ground has been enriched with plenty of organic matter. Big Leaf Hydrangeas are the species that grow best in the shade... The Best Hydrangeas for Growing Under Pine Trees The best species of hydrangea to grow in shadier conditions is Hydrangea macrophylla commonly called ‘Bigleaf hydrangeas’. There are many cultivars of this species that produce beautiful flowers of many different colours to suit your personal taste and notably turn out luxuriant foliage (as the name suggests) and will looks attractive when the hydrangea is not in flower. Bigleaf hydrangeas will produce flowers even in the shade and dappled light, but the more sunlight it receives the better the display will be. Fertilizer is Necessary Under Pine Trees Hydrangeas often don’t need fertilizer if they are in good soil amended with lots of organic matter and receive generous mulch once or twice per year. However pine trees and hydrangeas both have relatively shallow root systems and therefore will both be in direct competition for nutrients so it is a good idea to add some feed to make sure they are not starved of the nutrients they need to produce flowers. Hydrangeas are not fussy feeders so fortunately you can give them a general plant feed once in spring (March/April) and then another feed in July to ensure a good display of flowers and healthy foliage. There are however specific fertilizers for hydrangeas which I would recommend if you have poor sandy soils with low fertility. Granular slow release fertilizers are my favourite as they require only two applications per year and, as long as you follow the manufacturer’s instructions there is a low risk of over fertilizing your hydrangea which can burn the roots. Fertilizing should be done in conjunction with adding mulch as the mulch acts as a sponge to soak up water and maintain soil moisture, as well as adding nutrients. To add granular fertilizer it is best to rake back your mulch and apply the granules to the soil underneath then rake the mulch back into place of the top of the fertilizer. Do not apply any fertilizer after the middle of August as this will stimulate new softer growth at a time when the plant needs to direct its resources to preparing for its winter dormancy. Conclusion Growing Hydrangeas under pine trees is possible if there is some sunlight able to reach the ground below. The Bigleaf hydrangea species is most suited to growing in dappled light or partial shade conditions. The canopy of pine trees can stop rain water from reaching the soil below and the shallow root system can dry the ground beneath so it is important that you water you hydrangea regularly during the growing season with around a gallon of water every two or three days. Amending the soil with plenty of organic matter and adding regular mulch will be of great benefit retain moisture in the soil so that the hydrangea doesn’t suffer drought. Adding fertilizer is often necessary as both pine trees and hydrangeas have shallow roots systems which compete for the same nutrients. A granular feed twice a year will encourage luxuriant healthy leaves and a strong display of fabulous flowers and scents.