Please find the following links that can be very useful with regard to your garden and plants:

The Royal Horticultural Society
Useful for all topics related to plants and gardening

Shoot Gardening
Useful for plant information and gardening advice

Sage Gardener (Dave and Jane Newman)
For a range of gardening courses, talks and events in and around Lincolnshire, many at Doddington Hall which is an approved Royal Horticultural Society Qualifications Centre

Royal Horticultural Society.
AGM awards and plant hardiness catergories.
We note on our own labels if a plant has been given an 'Award of Garden Merit (AGM) by using the appropriate RHS symbol as shown below. 
To receive an AGM each plant must meet the following criteria;
1. Be excellent for ordinary use in appropriate conditions.
2. Be available
3. Be of good constitution
4. Essentially stable in form and colour.
5. Be reasonably resistant to pests and diseases.
Awards are only made after assessment by one or more RHS plant committees or advisory groups. Assessments often include a period of trial, which usually takes place at one of the four RHS Gardens. Each committee has its own area of expertise, and draws upon the experience of a wide range of experts, including nurserymen, specialist growers and well-known horticulturists.
If a plant does not have an AGM it does not mean that it is not garden worthy!!!!!!! It may never have been examined or it might be scarce.
Along with each AGM a hardiness rating will be given. 
For example - Magnolia 'Star Wars' (AGM-H5) 

RHS hardiness rating

The RHS has devised a system of hardiness ratings to enable gardeners to assess the hardiness of garden plants

The hardiness rating serves as a general guide to growing conditions, and should be interpreted as follows;

H1a        warmer than 15C.   Heated glasshouse - tropical. Needs to be grown as a house plant or under glass all year round.

H1b        10 to 15C.   Heated glasshouse - subtropical. Can be grown outdoors in summer in sunny and sheltered locations but generally performs best as a house plant or under glass all year round.

H1c         5 to 10C.  Heated glasshouse - warm temperate. Can be grown outdoors in summer throughout most of the UK while daytime temperatures are high enough to promote growth.

H2           1 to 5C.  Tender - cool or frost-free glasshouse. Tolerant of low temperatures but will not survive being frozen. Except in frost-free inner-city areas or coastal extremities requires glasshouse conditions in winter, but can be grown outdoors once risk of frost is over

H3           -5 to 1C.  Half-hardy - unheated glasshouse / mild winter. Hardy in coastal / mild areas except in hard winters and at risk from sudden (early) frosts. May be hardy elsewhere with wall shelter or good microclimate. Can survive with artificial winter protection.

H4           -10 to -5C.  Hardy - average winter.  Hardy through most of the UK apart from inland valleys, at altitude and central / northerly locations. May suffer foliage damage and stem dieback in harsh winters in cold gardens. Plants in pots are more vulnerable.

H5           -15 to -10C.  Hardy - cold winter.  Hardy through most of the UK even in severe winters. May not withstand open or exposed sites or central / northerly locations. Many evergreens suffer foliage damage and plants in pots will be at increased risk.

H6           -20 to -15C. Hardy - very cold winter. Hardy throughout the UK and northern Europe. Many plants grown in containers will be damaged unless given protection.

H7           colder than -20C.  Very hardy. Hardy in the severest European continental climates including exposed upland locations in the UK.

A point to note.............The above is the new hardiness system introduced by the RHS and supersedes the previous H1-H4 ratings. This was a nightmare for nurseries that had produced websites and labelling systems based on the old ratings. It is possible that some plants listed on our site have their old hardiness rating. (H4 on the old rating was very hardy!)
  Site Map