Hostas can grow well in moderate clay soils if the planting area is amended with organic matter to a depth of 12 inches. In heavy clay, regular mulching is important to improve drainage and ease soil compaction to allow the roots to establish and prevent water logged soil which can lead to root rot.
To grow hostas in clay successfully you will need to know:
- The problems associated with growing hostas in clay soils (so you can avoid them)
- How to amend clay soils properly before planting hostas
- What to do for hostas already in clay soils (that may be struggling)
- The best hostas for planting in clay soils
Problems of Growing Hostas in Clay Soil
Hostas can struggle to grow in clay soils for three major reasons:
- In particularly heavy or compacted clay the roots of the hosta will have a hard time growing down deep enough into the soil to access water, nutrients and gain enough purchase for the stability that they need.
- Clay soils have a tendency to bake hard in the summer sun which causes water to run off the surface instead of draining into the soil and reaching the roots of the hosta.
- Hostas do need to be regularly watered (most varieties need a good soak twice a week in the growing season), however they do not like it when their roots are sitting it water. In clay soils water often pools or drains away very slowly. Persistent exposure to water logged soil will lead to root rot in most varieties of hostas
How to Amend Clay Soil before Planting Hostas
If your soil contains a moderate amount of clay and still manages to drain well (such as loam soil) then you will not necessarily need to significantly amend the soil prior to planting.
However if you have a high proportion of clay in your soil and the ground drains noticeably slowly after significant rainfall then you will need to prepare the soil before planting.
If you are unsure a good test is to leave the hose pipe running on the area where you want to plant for a few minutes and then observe how quickly the water drains away.
If the water has formed a puddle or perhaps the water runs straight off the surface and has not infiltrated through the soil then you will have to add significant organic matter to remedy the situation.
- The first step is to dig the hole to a depth of around 16 inches for larger hosta varieties and 12 inches for smaller hostas as this is the right depth to accommodate the root system of a mature plant. The width of your hole will differ according to the size of your hosta but it is a good idea to make the width equal to the depth or proportional to the root ball of your hosta. A depth of 16 inches may seem excessive but You want a buffer zone of compost or sand between the bottom of the roots and the clay soil underneath so that water does not collect directly underneath the roots.
- Lay 2 inches of compost, sand or grit in the bottom of the hole which will provide the loose soil structure that will allow water to drain away from the roots as the bottom of the hole.
- Place your hosta in the ground making sure that the roots will be buried but the crown of the hosta (the knot at which the roots attach to the individual stems) is above ground. It is a good idea to use a stick of bamboo to make sure the crown is at roughly the right height before planting.
- Fill in the hole around the root system of your hosta with organic material such as garden compost, leaf mould, well rotted horse manure (fresh manure will burn the roots) or multipurpose compost bought from a garden centre. All of these amendments will be at the right pH for growing hostas (between pH 6-7) and they will provide the appropriate soil structure and drainage conditions for the roots of your hosta. Organic material such as compost has a good capacity for absorbing water yet allows excess water to drain away thanks to its open structure, which is the perfect balance for growing hostas.
- Do not firm the soil around the hosta after planting as hostas do not like compacted soil. Instead water the area round the base of the plant and let the soil settle.If necessary add some more compost around the plant so that the ground is level.
- Give the hosta a generous amount of water straight after planting and really soak the soil as hostas are vulnerable to drying out after planting. 4 gallons of water twice a week for the first four weeks is ideal.
- Apply a 2 inch layer of mulch around the base of the hosta but leave a gap 6 inch gap between the mulch and the stems of your hosta. This mulch will help retain water, suppress weeds and stimulate soil ecology, all of which will be of tremendous benefit to your hosta.
Why it’s Important to Add Mulch to Hostas in Clay Soil
Applying mulch around hostas in clay soil beneficial for several reasons:
- Organic mulch such as leaf mould or horse manure is a great way to stimulate soil ecology and encourage earthworms which subsequently create channels in the soil that allows water to drain away more effectively and creates space for roots to grow which is imperative to counteract heavy clay soil that can restrict root growth of hostas.
- The organic mulch will be incorporated into the soil naturally by the action of earthworms and the rain. This will change the profile of clay soil from thick and impermeable to a better, more porous texture that allows for good drainage.
- Clay soils are prone to compaction, most often from when you have to stand on the soil bed for weeding or watering which will make life difficult for your hosta. Mulching twice a year is the best way to ease soil compaction.
- Clay soils can bake hard in the summer which will either cause your watering or rainfall to run off the surface or into cracks in the soil and therefore the water never reaches the roots of your hosta. A layer of mulch will keep the underlying soil cool and prevent it from cracking. If the surface is covered in a layer of mulch water is also far more likely so infiltrate into the soil rather then run off the surface.
The best mulch for hostas planted in clay soils is leaf mould or general garden compost as this has a great capacity for retaining water and keeping the conditions suitable for the hosta. They will also add fertility to the soil and keep the weeds down which gives you more time to enjoy your garden!
Applying the mulch twice a year, with the first application in spring to help retain water during the growing season and the second application in the fall to help insulate the roots of your hosta from the worst of the winter cold which will give the hosta a head start when the weather warms up again for the new growing season.
I would advise against using wood chip or pine needles as mulch on clay soils as these materials can take years to decompose and the therefore take a long time improve the structure of the clay soil.
What to do for Hostas Already Growing in Clay Soils (How to help them)
Lets say you have inherited a garden with hostas in clay soil or you have planted hostas in clay and they are struggling to become establish, then do not worry.
Hostas are perhaps the most hardy foliage perrieneal plant that are cultivated for gardens when it comes to moving, dividing and not suffering from ‘transplant shock’.
In fact hostas are so hardy that you can move, divide or transplant them at anytime of the year without fear of killing the plant.
This means you can use a fork and gently tease out your hostas from the ground. Loosen and work the ground around the hostas with the fork around the hosta so you can free the roots without harming them.
Do not attempt to liberate your hosta with a spade as the edge of a spade takes no prisoners and may slice through the roots of the hosta.
Once you have freed you hosta you can simply amend the clay soil from which they came with plenty of organic matter. Leaf mould is ideal as it has a good capacity for holding moisture which is perfect for the roots of your hosta.
Work the organic matter to a depth of around 12 inches (or more if you have a large hosta cultivar) and if there is slow drainage in the planting area, throw in some grit or sand to help water infiltrate more freely. Two thirds leaf mould to one third grit is perfect for creating the right conditions.
Simply replant your hosta in its newly renovated home and give it the soil a generous soak with around 4 gallons of water. Water with 4 gallons twice a week for the first four weeks after replanting or transplanting hostas.
Afterwards apply mulch of either garden compost, more leaf mould or well rotted manure around your hosta to help retain water.
Remember you can move, divide or transplant hostas at anytime of the year so if you see your hosta struggling in clay soil due to water logged soil or a soil surface that is compacted and baked hard, it is better to act sooner rather then later.
Best Hosta Varieties for Clay Soils
Simply put, bigger hostas do better in clay soils then smaller hostas. This is because smaller hostas often have difficulty establishing there roots systems in heavy soil.
Bigger hosta varieties naturally a more extensive roots system and can establish in clay soils more quickly to access water, nutrients and maintain plant stability
This isn’t to say you cannot plant small hostas in clay soil but you will have to add plenty of organic material to the area when planting and diligently add mulch around the hostas twice per season.
Classic large varities of hostas that do well in properly amended clay soils include ‘blue angle’, ‘jade cascade’ and ‘Atlantis’
Hostas will do very well in clay soils as long as they are properly amended first with organic matter such as leaf mould or garden compost. These materials provide the ideal conditions for the hostas roots which is to hold moisture but to allow excess water to drain away.
Mulching is very important to maintain the correct soil structure and also helps maintain the correct soil pH (pH 6-7 is optimal for growing hostas) as clay soils are prone to compaction which hinders water infiltrating and reaching the roots of your hosta.
Larger varieties tend to do better in clay soils however if you have diligently amended the planting area and keep up a regular schedule of mulching then you will be able to grow any size and variety of hosta you like.
Hostas are some of the hardiest garden plants when it comes to moving or transplanting so you can rescue hostas that have been planted into heavy clay soil and are struggling. Simply fork out the hosta, add some organic matter and replant the hosta. It is suitable to do this at anytime of year thanks to the hostas natural hardiness.