The Icecream Bean Tree – Inga

The genus Inga is commonly referred to as Ice Cream Bean due to the characteristic white, fluffy, melt-in-your-mouth pulp surrounding each seed. Pal­atability varies from species to species. In the humid sub-tropics of northern New South Wales, Inga mor­toniana, of aU the species tried, is both the best adapt­ed and tastiest. The original material on the North Coast was coUected in a highland Central American market-place.( 1).

Other species of Inga on trial (I. spec­tabalis, I. coxil. I. paterno) have all grown strongly, and all make strikingly handsome specimen trees but none have fruited well. Ingas have also been tnalled with success in Sarawak. Ma­laysia. Contral)’ to published data (2) which states that isolated Inga trees do not bear fruit because they are self­ incompatible, all the non-bearing spe­cies I have planted here have partners within pollinating distance, and the original Inga mortoniana tree was on its own when bearing huge crops. Bear­ing commenced at three years with hun­dreds of 7-20cm golden yellow pods by five years.

Nitrogen Fixing

The most outstanding feature of Inga mortoniana is the massive production of nitrogen fixing nodules. I have never witnessed such massive numbers of nodules on any other legume. Last year, digging four metres away from the nearest Inga, I found that the roots were heavily laced with nodules like strung pearls on all available root surfaces. This feature combined with the ease of growing in the nursery and establish­ment in the field make this species ex­tremely useful for soil rejuvenation. With that aim in mind, I planted over 400 trees in a paddock which I have in­terplanted with a range of other species. This, their fourth year, found me for the first time going at them with the chain­saw lopping branches and letting them lie as trash as I try to recreate the forest floor in as short a time as my low maintenance program will allow.

Intriguingly, seeds are polyembryon­ic, which is weird and unexpected in a pioneer species where one would ex­pect the opposite. To whit: great varia­tion in the gene pool to maximise adap­tation to various sites. With excellent coppicing ability, these trees can be continually cut back. If at any time the trees need to be removed, chainsawing at ground level and repeated slashing will kill them as their underground parts rot to the total restoration of soil health. Trees are readily propagated by directly sowing seed into 150 mm pots and they are ready for field planting in a year. All my trees have been estab­lished from 150 mm pots.

Pests

Inga mortoniana is the only species to ever have mites in the field here, but this was only on a couple of trees; it went untreated and disappeared. The biggest pest problem is a seed borer that can damage up to 90% of the pods, ren­dering them unsuitable for sale but not for consumption as only part of the pod is riddled.

Adaptability and Value

This species has proven adaptable to all sites from constantly moist to dl)’, heavy soils to light soils, and is hardy to at least -3C. I even planted 60 trees 400 mm apart on good quality basalt soil. After three years trees were an effective windbreak four metres high and fruit­ing! The new growth is an attractive reddish-bronze and the white flowers pretty. All Inga species have amazingly shaped pinnate leaves. Traditionally some Inga species (I. vera) have been used as shade and support trees (coffee, vanilla, pepper) in plantations. Most In­gas have valuable timber properties; judging by the density of Inga mortoni­ana wood at such an early age, this is a particularly valuable species. The only limitation is strong tendency to branch. Ingas are also good fodder and street trees.

This species is naturalising and over time could prove to be competitive with Australian pioneers such as Acacia melanoxylon. Even with that possibility, this is an outstanding multi-purpose tree.