Environment is everything to hostas.

To get a mature hosta as pictured in catalogues and on web sites requires a combination of the appropriate soils, moisture, fertility, light and pH conditions.

Gardeners are used to considering the first three gardening variables. The more we garden, the more we see the detrimental effects of our alkaline water on the success of many of our plants. As a result, both around the nursery and in our gardens, we are paying much more attention to the water quality applied to certain plants. Hostas do best with slightly acidic soil conditions. So we are acidifying our irrigation water for acid-loving plants like hostas. More on this later.

What Soils are Best for Hostas?

Hostas require consistent moisture to compensate for high moisture losses from their large leaves due to transpiration. They also want soils with lots of air spaces to provide oxygen for their internal biological processes. Pure sand and pure clay are tough on hostas. The former has no moisture retention capability and the later poor air space structure. Can you grow hosta in sand and clay? In clay some hostas will survive, but not thrive. I wouldn’t bother to try hostas in straight sand.

Most Otttawa -area gardeners are going to have to construct good hosta-growing soil due to our native soil conditions. A sandy-clay-loam offers the best soil structure for hostas. Commercial hosta grower Mark Zilis (owner of Q and Z Nursery in Rochelle, Illinois) recommends adding 8-12 cubic feet of peat moss per 100 square feet of hosta planting area. The American Hosta Society recommends a soil which has 1/3 native soil,1/3 peat humus (some use ProMix as an alternative to the peat humus), and 1/3 pine bark fines (some use other larger material). Hosta roots can easily grow into the soil to depths of 12 inches. Accordingly, soils should be deeply prepared to this depth as a minimum. Hostas are long-lived perennials and will benefit from this extra site preparation work.Hostas prefer a slightly acidic soil for optimum nutrient uptake. Their preference is a pH from 6.0 to 6.5. More alkaline soils (the rule around Ottawa) benefit from the addition of purchased elemental sulfur to establish acidic soil conditions. Sulfur should be applied sparingly (just enough to turn the soil surface yellow)and worked into the soil and left for a couple of weeks before planting time. The peat moss will maintain the acidic conditions as it naturally decomposes.

Hostas are heavy feeders, so humus formed from kitchen and garden wastes is an excellent substitution for peat humus which is low in nutrients.

What fertilizer should I use for my hosta?

The author of "The Genus Hosta", (the hosta ‘bible’) George Schmid reports that his fertilizer choice is a pelletized commercial slow-release fertilizer called Osmocote 18-6-12 that costs about $150.00 Cdn per 20 kg. bag. Apply the fertilizer around the base of each hosta as the they begin growth each spring. Two tablespoons of the pellets should be adequate for larger mature hosta clumps.

For organic-minded gardeners, there are several products available. Milorganite (composted sewage sludge from Milwaukee) has been commercially available for years. The City of Ottawa now has a city dump waste diversion program in which a vegetative compost is produced. That product should also be appropriate. Another alternative is 2 year old animal manure. Beware the potential for "burning” hostas with "fresh" manure.

How much Water?

Knowing something about the native origin of plants helps provide guidance to success with garden plants. Hostas are native to the Pacific Rim countries such as Japan, Korea and China. These are not dry areas of the world! Sixty inches of rain per year (on average) is common in Japan. Around Ottawa we are lucky to get one third of that during the active growing season.

A regular watering schedule should be considered for hostas to get them to grow to their full potential. Ensure that the plant receives a minimum of 1 inch per week during the growing season for adequate growth. Overhead watering should be avoided: drip irrigation or soaker hoses are the best. Water deeply rather than frequently. The aim is to get the entire root zone thoroughly moistened to a depth of at least 12 inches. Then let the first 2 inches of surface soil become dry before watering again. Hosta roots, like all roots, need ample oxygen for their biological functioning. The deep watering drives air out from the soil pores and, as the soils dry out, new air is drawn back into the soil pores. This pulsing of moisture regimes is like our breathing – it keeps fresh oxygen around the living root tissues.

If you see wilting hosta leaves, begin watering right away. Drooping leaves is a symptom that the plant will also soon turned off other biological functions (photosynthesis and water circulation) which will affect hosta growth. Hostas, like most plants, perform best when they have not been stressed. They can recover, but they will not reach their potential size or beauty in that season.

Application of organic mulches to the soil around the bases of hostas, especially in wind-prone areas, is beneficial. Bark or other previously composed materials are ideal for preventing moisture loss. They should be applied to a depth of not greater than two inches. Mushroom or garden compost, applied (in 1/2 inch quantities) in spring for nutritional purposes should be applied before the moisture-retention mulches are put in place.

Hostas prefer water with a pH between 6.0 and 7.0. This slightly acidic condition promotes effective absorption of nutrients from the soil and gives optimum growth results. In the Ottawa area gardeners are likely to encounter alkaline water with a pH from 7.0 to 8.5 – definitely not conducive to growing the picture-perfect hosta. Further information on tap water pH can be found at www.rcgardens.ca/factsheets/tap waterinfo.html

What about light conditions for hostas?

In native settings, hostas grow where they take advantage of early season direct sunlight but are shaded by other taller plants later in the season.

Forest-edges, forest-openings and damp meadows full of tall grasses and shrubs are typical sites. The American Hosta Society points out that hosta are really shade tolerant plants and not shade-loving plants. They offer two general rules of thumb: "the greener the leaf, the less sun necessary for the plant to grow well” and (a corollary rule) "the more yellow and white in a leaf, the more sun necessary for sufficient photosynthesis to allow the plant to thrive."

Hostas should not be placed in dark areas where nothing else grows. They may exist, but they won’t flower or thrive. Ideally, hostas benefit from early morning direct sunshine and filtered sunlight the rest of the day. Commercial hosta producers grow hostas in open fields like corn! That is an indication of how much sun many hostas utilize.

Blue-green hostas succeed in shady damp places and keep their blue-green coloration longer in shade than in sun. Hostas with green, chartreuse, and yellow leaves can tolerate quite a lot of direct sunlight as long as their root systems are kept uniformly moist.

As mentioned above, hostas in full sun need extra moisture. Watch for wilting as a sign that extra water is needed immediately.

Will hostas retain their advertised leaf colour all season?

You can expect a variety of seasonal leaf-colour changes especially in multi-coloured leaf types. Some blue hostas may also ‘change’ to green later in the season. The hosta world has a number of technical terms describing these changes. The American Hosta Society website http://www.hosta.org/hostafaq.htm has more information on this topic.